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4-CLASS.html
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<!DOCTYPE html><html lang="zh-CN"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width,height=device-height,initial-scale=1.0"><meta name="apple-mobile-web-app-capable" content="yes"><meta http-equiv="X-UA-Compatible" content="ie=edge"><meta property="og:type" content="website"><meta name="twitter:card" content="summary"><style>@media screen{body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button{appearance:none;background-color:initial;border:0;color:inherit;cursor:pointer;font-size:inherit;opacity:.8;outline:none;padding:0;transition:opacity .2s linear;-webkit-tap-highlight-color:transparent}body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button:disabled,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button:disabled,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button:disabled,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button:disabled{cursor:not-allowed;opacity:.15!important}body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button:hover,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button:hover,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button:hover,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button:hover{opacity:1}body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button:hover:active,body[data-bespoke-view=next] 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url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAxMDAgMTAwIj48cGF0aCBmaWxsPSJub25lIiBzdHJva2U9IiNmZmYiIHN0cm9rZS1saW5lY2FwPSJyb3VuZCIgc3Ryb2tlLWxpbmVqb2luPSJyb3VuZCIgc3Ryb2tlLXdpZHRoPSI1IiBkPSJNODcuOCA0Ny41Qzg5IDUwIDg3LjcgNTIgODUgNTJIMzVhOC43IDguNyAwIDAgMS03LjItNC41bC0xNS42LTMxQzExIDE0IDEyLjIgMTIgMTUgMTJoNTBhOC44IDguOCAwIDAgMSA3LjIgNC41ek02MCA1MnYzNm0tMTAgMGgyME00NSA0MmgyMCIvPjwvc3ZnPg==") no-repeat 50%;background-size:contain;overflow:hidden;text-indent:100%;white-space:nowrap}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button.bespoke-marp-presenter-note-bigger{background:#0000 url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAxMDAgMTAwIj48cGF0aCBzdHJva2U9IiNmZmYiIHN0cm9rZS1saW5lY2FwPSJyb3VuZCIgc3Ryb2tlLWxpbmVqb2luPSJyb3VuZCIgc3Ryb2tlLXdpZHRoPSI1IiBkPSJNMTIgNTBoODBNNTIgOTBWMTAiLz48L3N2Zz4=") no-repeat 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.bespoke-marp-presenter-note-buttons{background:#000000a6;border-radius:4px;bottom:0;display:flex;gap:4px;margin:12px;opacity:0;padding:6px;pointer-events:none;position:absolute;right:0;transition:opacity .2s linear}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-presenter-note-buttons:focus-within,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-presenter-note-wrapper:focus-within+.bespoke-marp-presenter-note-buttons,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container:hover .bespoke-marp-presenter-note-buttons{opacity:1;pointer-events:auto}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note{box-sizing:border-box;font-size:calc(1.1em*var(--bespoke-marp-note-font-scale, 1));height:calc(100% - 40px);margin:20px;overflow:auto;padding-right:3px;white-space:pre-wrap;width:calc(100% - 40px);word-wrap:break-word;scrollbar-color:#eeeeee80 #0000;scrollbar-width:thin}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note::-webkit-scrollbar{width:6px}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note::-webkit-scrollbar-track{background:#0000}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note::-webkit-scrollbar-thumb{background:#eeeeee80;border-radius:6px}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note:empty{pointer-events:none}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note.active{display:block}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note p:first-child{margin-top:0}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container .bespoke-marp-note p:last-child{margin-bottom:0}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container{align-items:center;box-sizing:border-box;color:#eee;display:flex;flex-wrap:nowrap;grid-area:info;justify-content:center;overflow:hidden;padding:0 10px}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-page,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-time,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-timer{box-sizing:border-box;display:block;padding:0 10px;white-space:nowrap;width:100%}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button{height:1.5em;line-height:1.5em;width:1.5em}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-page{order:2;text-align:center}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-page .bespoke-marp-presenter-info-page-text{display:inline-block;min-width:120px;text-align:center}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-time{color:#999;order:1;text-align:left}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-timer{color:#999;order:3;text-align:right}body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container .bespoke-marp-presenter-info-timer:hover{cursor:pointer}}@media print{.bespoke-marp-presenter-info-container,.bespoke-marp-presenter-next-container,.bespoke-marp-presenter-note-container{display:none}}</style><style>@charset "UTF-8";@import "https://fonts.bunny.net/css?family=Lato:400,900|Roboto+Mono:400,700&display=swap";div#\:\$p > svg > foreignObject > section{width:1280px;height:720px;box-sizing:border-box;overflow:hidden;position:relative;scroll-snap-align:center center;-webkit-text-size-adjust:100%;text-size-adjust:100%}div#\:\$p > svg > foreignObject > section::after{bottom:0;content:attr(data-marpit-pagination);padding:inherit;pointer-events:none;position:absolute;right:0}div#\:\$p > svg > foreignObject > section:not([data-marpit-pagination])::after{display:none}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1){font-size:2em;margin:0.67em 0}div#\:\$p > svg > foreignObject > section video::-webkit-media-controls{will-change:transform}@page {size:1280px 720px;margin:0}@media print{html, body{background-color:#fff;margin:0;page-break-inside:avoid;break-inside:avoid-page}div#\:\$p > svg > foreignObject > section{page-break-before:always;break-before:page}div#\:\$p > svg > foreignObject > section, div#\:\$p > svg > foreignObject > section *{-webkit-print-color-adjust:exact!important;animation-delay:0s!important;animation-duration:0s!important;color-adjust:exact!important;transition:none!important}div#\:\$p > svg[data-marpit-svg]{display:block;height:100vh;width:100vw}}div#\:\$p > svg > foreignObject > :where(section){container-type:size}div#\:\$p > svg > foreignObject > section img[data-marp-twemoji]{background:transparent;height:1em;margin:0 .05em 0 .1em;vertical-align:-.1em;width:1em}/*!
* Marp / Marpit Gaia theme.
*
* @theme gaia
* @author Yuki Hattori
*
* @auto-scaling true
* @size 16:9 1280px 720px
* @size 4:3 960px 720px
*/div#\:\$p > svg > foreignObject > section :is(pre, marp-pre) code.hljs{display:block;overflow-x:auto;padding:1em}div#\:\$p > svg > foreignObject > section code.hljs{padding:3px 5px}div#\:\$p > svg > foreignObject > section .hljs{background:#000;color:#f8f8f8}div#\:\$p > svg > foreignObject > section .hljs-comment,div#\:\$p > svg > foreignObject > section .hljs-quote{color:#aeaeae;font-style:italic}div#\:\$p > svg > foreignObject > section .hljs-keyword,div#\:\$p > svg > foreignObject > section .hljs-selector-tag,div#\:\$p > svg > foreignObject > section .hljs-type{color:#e28964}div#\:\$p > svg > foreignObject > section .hljs-string{color:#65b042}div#\:\$p > svg > foreignObject > section .hljs-subst{color:#daefa3}div#\:\$p > svg > foreignObject > section .hljs-link,div#\:\$p > svg > foreignObject > section .hljs-regexp{color:#e9c062}div#\:\$p > svg > foreignObject > section .hljs-name,div#\:\$p > svg > foreignObject > section .hljs-section,div#\:\$p > svg > foreignObject > section .hljs-tag,div#\:\$p > svg > foreignObject > section .hljs-title{color:#89bdff}div#\:\$p > svg > foreignObject > section .hljs-class .hljs-title,div#\:\$p > svg > foreignObject > section .hljs-doctag,div#\:\$p > svg > foreignObject > section .hljs-title.class_{text-decoration:underline}div#\:\$p > svg > foreignObject > section .hljs-bullet,div#\:\$p > svg > foreignObject > section .hljs-number,div#\:\$p > svg > foreignObject > section .hljs-symbol{color:#3387cc}div#\:\$p > svg > foreignObject > section .hljs-params,div#\:\$p > svg > foreignObject > section .hljs-template-variable,div#\:\$p > svg > foreignObject > section .hljs-variable{color:#3e87e3}div#\:\$p > svg > foreignObject > section .hljs-attribute{color:#cda869}div#\:\$p > svg > foreignObject > section .hljs-meta{color:#8996a8}div#\:\$p > svg > foreignObject > section .hljs-formula{background-color:#0e2231;color:#f8f8f8;font-style:italic}div#\:\$p > svg > foreignObject > section .hljs-addition{background-color:#253b22;color:#f8f8f8}div#\:\$p > svg > foreignObject > section .hljs-deletion{background-color:#420e09;color:#f8f8f8}div#\:\$p > svg > foreignObject > section .hljs-selector-class{color:#9b703f}div#\:\$p > svg > foreignObject > section .hljs-selector-id{color:#8b98ab}div#\:\$p > svg > foreignObject > section .hljs-emphasis{font-style:italic}div#\:\$p > svg > foreignObject > section .hljs-strong{font-weight:700}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1),div#\:\$p > svg > foreignObject > section :is(h2, marp-h2),div#\:\$p > svg > foreignObject > section :is(h3, marp-h3),div#\:\$p > svg > foreignObject > section :is(h4, marp-h4),div#\:\$p > svg > foreignObject > section :is(h5, marp-h5),div#\:\$p > svg > foreignObject > section :is(h6, marp-h6){margin:.5em 0 0}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1) strong,div#\:\$p > svg > foreignObject > section :is(h2, marp-h2) strong,div#\:\$p > svg > foreignObject > section :is(h3, marp-h3) strong,div#\:\$p > svg > foreignObject > section :is(h4, marp-h4) strong,div#\:\$p > svg > foreignObject > section :is(h5, marp-h5) strong,div#\:\$p > svg > foreignObject > section :is(h6, marp-h6) strong{font-weight:inherit}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h2, marp-h2)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h3, marp-h3)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h4, marp-h4)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h5, marp-h5)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h6, marp-h6)::part(auto-scaling){max-height:580px}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1){font-size:1.8em}div#\:\$p > svg > foreignObject > section :is(h2, marp-h2){font-size:1.5em}div#\:\$p > svg > foreignObject > section :is(h3, marp-h3){font-size:1.3em}div#\:\$p > svg > foreignObject > section :is(h4, marp-h4){font-size:1.1em}div#\:\$p > svg > foreignObject > section :is(h5, marp-h5){font-size:1em}div#\:\$p > svg > foreignObject > section :is(h6, marp-h6){font-size:.9em}div#\:\$p > svg > foreignObject > section blockquote,div#\:\$p > svg > foreignObject > section p{margin:1em 0 0}div#\:\$p > svg > foreignObject > section ol>li,div#\:\$p > svg > foreignObject > section ul>li{margin:.3em 0 0}div#\:\$p > svg > foreignObject > section ol>li>p,div#\:\$p > svg > foreignObject > section ul>li>p{margin:.6em 0 0}div#\:\$p > svg > foreignObject > section code{display:inline-block;font-family:Roboto Mono,monospace;font-size:.8em;letter-spacing:0;margin:-.1em .15em;padding:.1em .2em;vertical-align:baseline}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre){display:block;margin:1em 0 0;overflow:visible}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre) code{box-sizing:border-box;font-size:.7em;margin:0;min-width:100%;padding:.5em}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre)::part(auto-scaling){max-height:calc(580px - 1em)}div#\:\$p > svg > foreignObject > section blockquote{margin:1em 0 0;padding:0 1em;position:relative}div#\:\$p > svg > foreignObject > section blockquote:after,div#\:\$p > svg > foreignObject > section blockquote:before{content:"“";display:block;font-family:Times New Roman,serif;font-weight:700;position:absolute}div#\:\$p > svg > foreignObject > section blockquote:before{left:0;top:0}div#\:\$p > svg > foreignObject > section blockquote:after{bottom:0;right:0;transform:rotate(180deg)}div#\:\$p > svg > foreignObject > section blockquote>:first-child{margin-top:0}div#\:\$p > svg > foreignObject > section mark{background:transparent}div#\:\$p > svg > foreignObject > section table{border-collapse:collapse;border-spacing:0;margin:1em 0 0}div#\:\$p > svg > foreignObject > section table td,div#\:\$p > svg > foreignObject > section table th{border-style:solid;border-width:1px;padding:.2em .4em}div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header,div#\:\$p > svg > foreignObject > section:after{box-sizing:border-box;font-size:66%;height:70px;line-height:50px;overflow:hidden;padding:10px 25px;position:absolute}div#\:\$p > svg > foreignObject > section:after{--marpit-root-font-size:66%;}div#\:\$p > svg > foreignObject > section header{top:0}div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header{left:0;right:0}div#\:\$p > svg > foreignObject > section footer{bottom:0}div#\:\$p > svg > foreignObject > section{background-color:var(--color-background);background-image:linear-gradient(135deg, hsla(0,0%,53%,0), hsla(0,0%,53%,.02) 50%, hsla(0,0%,100%,0) 0, hsla(0,0%,100%,.05));color:var(--color-foreground);font-family:Lato,Avenir Next,Avenir,Trebuchet MS,Segoe UI,sans-serif;font-size:35px;height:720px;letter-spacing:1.25px;line-height:1.35;padding:70px;width:1280px;word-wrap:break-word;--color-background:#fff8e1;--color-background-stripe:rgba(69,90,100,.1);--color-foreground:#455a64;--color-dimmed:#6a7a7d;--color-highlight:#0288d1;}div#\:\$p > svg > foreignObject > section{--marpit-root-font-size:35px;}div#\:\$p > svg > foreignObject > section:after{bottom:0;font-size:80%;right:0}div#\:\$p > svg > foreignObject > section:after{--marpit-root-font-size:80%;}div#\:\$p > svg > foreignObject > section a,div#\:\$p > svg > foreignObject > section mark{color:var(--color-highlight)}div#\:\$p > svg > foreignObject > section code{background:var(--color-dimmed);color:var(--color-background)}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1) strong,div#\:\$p > svg > foreignObject > section :is(h2, marp-h2) strong,div#\:\$p > svg > foreignObject > section :is(h3, marp-h3) strong,div#\:\$p > svg > foreignObject > section :is(h4, marp-h4) strong,div#\:\$p > svg > foreignObject > section :is(h5, marp-h5) strong,div#\:\$p > svg > foreignObject > section :is(h6, marp-h6) strong{color:var(--color-highlight)}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre){background:var(--color-foreground)}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre)>code{background:transparent}div#\:\$p > svg > foreignObject > section blockquote:after,div#\:\$p > svg > foreignObject > section blockquote:before,div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header,div#\:\$p > svg > foreignObject > section section:after{color:var(--color-dimmed)}div#\:\$p > svg > foreignObject > section table td,div#\:\$p > svg > foreignObject > section table th{border-color:var(--color-foreground)}div#\:\$p > svg > foreignObject > section table thead th{background:var(--color-foreground);color:var(--color-background)}div#\:\$p > svg > foreignObject > section table tbody>tr:nth-child(odd) td,div#\:\$p > svg > foreignObject > section table tbody>tr:nth-child(odd) th{background:var(--color-background-stripe, transparent)}div#\:\$p > svg > foreignObject > section>:first-child,div#\:\$p > svg > foreignObject > section>header:first-child+*{margin-top:0}div#\:\$p > svg > foreignObject > section:where(.invert){--color-background:#455a64;--color-background-stripe:rgba(255,248,225,.1);--color-foreground:#fff8e1;--color-dimmed:#dad8c8;--color-highlight:#81d4fa;}div#\:\$p > svg > foreignObject > section:where(.gaia){--color-background:#0288d1;--color-background-stripe:rgba(255,248,225,.1);--color-foreground:#fff8e1;--color-dimmed:#cce2de;--color-highlight:#81d4fa;}div#\:\$p > svg > foreignObject > section:where(.lead){align-items:stretch;flex-flow:column nowrap;place-content:safe center center}div#\:\$p > svg > foreignObject > section:where(.lead) :is(h1, marp-h1),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h2, marp-h2),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h3, marp-h3),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h4, marp-h4),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h5, marp-h5),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h6, marp-h6){text-align:center}div#\:\$p > svg > foreignObject > section:where(.lead) p{text-align:center}div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h1, marp-h1),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h2, marp-h2),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h3, marp-h3),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h4, marp-h4),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h5, marp-h5),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h6, marp-h6),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>p{text-align:left}div#\:\$p > svg > foreignObject > section:where(.lead) ol>li>p,div#\:\$p > svg > foreignObject > section:where(.lead) ul>li>p{text-align:left}div#\:\$p > svg > foreignObject > section:where(.lead) table{margin-left:auto;margin-right:auto}div#\:\$p > svg > foreignObject > section img{display:block;margin:0 auto}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]{columns:initial!important;display:block!important;padding:0!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]::before, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]::after, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"]::before, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"]::after{display:none!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container]{all:initial;display:flex;flex-direction:row;height:100%;overflow:hidden;width:100%}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container][data-marpit-advanced-background-direction="vertical"]{flex-direction:column}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"][data-marpit-advanced-background-split] > div[data-marpit-advanced-background-container]{width:var(--marpit-advanced-background-split, 50%)}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"][data-marpit-advanced-background-split="right"] > div[data-marpit-advanced-background-container]{margin-left:calc(100% - var(--marpit-advanced-background-split, 50%))}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container] > figure{all:initial;background-position:center;background-repeat:no-repeat;background-size:cover;flex:auto;margin:0}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container] > figure > figcaption{position:absolute;border:0;clip:rect(0, 0, 0, 0);height:1px;margin:-1px;overflow:hidden;padding:0;white-space:nowrap;width:1px}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"], div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="pseudo"]{background:transparent!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="pseudo"], div#\:\$p > svg[data-marpit-svg] > foreignObject[data-marpit-advanced-background="pseudo"]{pointer-events:none!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background-split]{width:100%;height:100%}
</style></head><body><div class="bespoke-marp-osc"><button data-bespoke-marp-osc="prev" tabindex="-1" title="Previous slide">Previous slide</button><span data-bespoke-marp-osc="page"></span><button data-bespoke-marp-osc="next" tabindex="-1" title="Next slide">Next slide</button><button data-bespoke-marp-osc="fullscreen" tabindex="-1" title="Toggle fullscreen (f)">Toggle fullscreen</button><button data-bespoke-marp-osc="presenter" tabindex="-1" title="Open presenter view (p)">Open presenter view</button></div><div id=":$p"><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-class="lead" data-theme="gaia" lang="zh-CN" class="lead" data-marpit-pagination="1" style="--paginate:true;--background-color:#fff;--class:lead;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:40%;" data-marpit-pagination-total="48" data-marpit-advanced-background="background" data-marpit-advanced-background-split="right"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("images/Java_logo.png");background-size:90%;"></figure></div></section></foreignObject><foreignObject width="60%" height="720"><section id="1" data-paginate="true" data-background-color="#fff" data-class="lead" data-theme="gaia" lang="zh-CN" class="lead" data-marpit-pagination="1" style="--paginate:true;--background-color:#fff;--class:lead;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:40%;" data-marpit-pagination-total="48" data-marpit-advanced-background="content" data-marpit-advanced-background-split="right">
<h1 id="java%E9%AB%98%E7%BA%A7%E7%A8%8B%E5%BA%8F%E8%AE%BE%E8%AE%A1">Java高级程序设计</h1>
<h2 id="%E7%B1%BB%E5%9E%8B%E7%B1%BB%E5%8A%A0%E8%BD%BD%E5%92%8C%E8%87%AA%E7%9C%81">类型、类加载和自省</h2>
</section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-class="lead" data-theme="gaia" lang="zh-CN" class="lead" data-marpit-pagination="1" style="" data-marpit-pagination-total="48" data-marpit-advanced-background="pseudo" data-marpit-advanced-background-split="right"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="2" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="2" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E5%9B%9E%E9%A1%BE%E4%B8%80%E4%B8%8B%E6%8A%BD%E8%B1%A1">回顾一下抽象</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Shape</span>{
<span class="hljs-keyword">void</span> <span class="hljs-title function_">draw</span><span class="hljs-params">()</span>{ System.out.println(<span class="hljs-string">"Draw Shape"</span>); }
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Circle</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Shape</span>{
<span class="hljs-keyword">void</span> <span class="hljs-title function_">draw</span><span class="hljs-params">()</span>{ System.out.println(<span class="hljs-string">"Draw Circle"</span>); }
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Triangle</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Shape</span>{
<span class="hljs-keyword">void</span> <span class="hljs-title function_">draw</span><span class="hljs-params">()</span>{ System.out.println(<span class="hljs-string">"Draw Triangle"</span>); }
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Square</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Shape</span>{
<span class="hljs-keyword">void</span> <span class="hljs-title function_">draw</span><span class="hljs-params">()</span>{ System.out.println(<span class="hljs-string">"Draw Square"</span>); }
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">Test</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
Shape[] shapes = {<span class="hljs-keyword">new</span> <span class="hljs-title class_">Circle</span>(), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Triangle</span>(), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Square</span>()};
<span class="hljs-keyword">for</span>(Shape s : shapes){
s.draw(); <span class="hljs-comment">// without knowing the concrete type of "s"</span>
}
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="3" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="3" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="what-if">What if?</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">abstract</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">Shape</span>{
<span class="hljs-keyword">void</span> <span class="hljs-title function_">draw</span><span class="hljs-params">()</span>{ System.out.println(<span class="hljs-string">"Draw Shape"</span>); }
<span class="hljs-keyword">abstract</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">rotate</span><span class="hljs-params">()</span>;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">Test</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
Shape[] shapes = {<span class="hljs-keyword">new</span> <span class="hljs-title class_">Circle</span>(), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Triangle</span>(), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Square</span>()};
<span class="hljs-keyword">for</span>(Shape s : shapes){
<span class="hljs-comment">// if s is not a circle </span>
s.rotate(); <span class="hljs-comment">// circle.rotate() means nothing!</span>
}
}
}
</code></pre>
<div style="text-align:center; color:red">如何在不破坏抽象的原则下获得对象的实际类型？</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="4" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="4" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="run-time-type-identification-rtti">Run-time type identification (RTTI)</h2>
<p>In computer programming, <strong>run-time type information or run-time type identification (RTTI)</strong> is a feature of the C++ programming language that exposes information about an object's data type at runtime. Run-time type information can apply to simple data types, such as integers and characters, or to generic types. This is a C++ specialization of a more general concept called <strong>type introspection</strong>. Similar mechanisms are also known in other programming languages, such as Object Pascal (Delphi).</p>
<div style="text-align:right">--Wikipedia</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="5" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="5" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="class"><code>Class</code></h1>
<p>每一个类都持有其对应的<code>Class</code>类的对象的引用，其中包含着与类相关的信息</p>
<ul>
<li><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Class.html">https://docs.oracle.com/javase/8/docs/api/java/lang/Class.html</a></li>
</ul>
<p><code>Object</code>类中的<code>getClass()</code>能让我们获取到这个对象</p>
<ul>
<li><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#getClass">https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#getClass</a></li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="6" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="6" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E8%AF%95%E4%B8%80%E4%B8%8B">试一下</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">import</span> java.util.ArrayList;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">PrintClass</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] ags)</span> {
System.out.println(<span class="hljs-string">"Class of this class:"</span> + <span class="hljs-keyword">new</span> <span class="hljs-title class_">PrintClass</span>().getClass());
System.out.println(<span class="hljs-string">"Class of ArrayList:"</span> + ArrayList.class);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="7" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="7" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E6%80%9D%E8%80%83%E4%B8%80%E4%B8%8B">思考一下</h2>
<p><code>Class</code>对象内的信息来自哪里？</p>
<p>针对每一个类，编译Java文件会生成一个二进制.class文件，这其中就保存着该类对应的Class对象的信息。</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-bash">javap HelloWorld.class
javap -v -p -s -sysinfo -constants HelloWorld.class
</code></pre>
<p><a href="https://docs.oracle.com/javase/8/docs/technotes/tools/windows/javap.html">https://docs.oracle.com/javase/8/docs/technotes/tools/windows/javap.html</a></p>
<blockquote>
<p>Java 字节码就是类型信息</p>
</blockquote>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="8" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:60%;" data-marpit-pagination-total="48" data-marpit-advanced-background="background" data-marpit-advanced-background-split="right"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("https://upload.wikimedia.org/wikipedia/commons/d/dd/JvmSpec7.png");background-size:contain;"></figure></div></section></foreignObject><foreignObject width="40%" height="720"><section id="8" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="8" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:60%;" data-marpit-pagination-total="48" data-marpit-advanced-background="content" data-marpit-advanced-background-split="right">
<h1 id="java-virtual-machine">Java Virtual Machine</h1>
<ul>
<li><small>类加载系统 （Class Loader Subsystem）</small></li>
<li><small>执行时数据区域（Runtime Data Area）</small></li>
<li><small>执行引擎（Execution Engine）</small></li>
</ul>
</section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="8" style="" data-marpit-pagination-total="48" data-marpit-advanced-background="pseudo" data-marpit-advanced-background-split="right"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="9" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="9" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="jvm-languages">JVM languages</h1>
<p>Apart from the <strong>Java</strong> language, other JVM languages are:</p>
<ul>
<li><small><strong>Clojure</strong>, a modern, dynamic, and functional dialect of the Lisp</small></li>
<li><small><strong>Groovy</strong>, a dynamic programming and scripting language</small></li>
<li><small><strong>JRuby</strong>, an implementation of Ruby</small></li>
<li><small><strong>Jython</strong>, an implementation of Python</small></li>
<li><small><strong>Kotlin</strong>, a statically-typed language from JetBrains</small></li>
<li><small><strong>Scala</strong>, a statically-typed object-oriented and functional programming language</small></li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="10" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="10" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E7%B1%BB%E5%8A%A0%E8%BD%BD%E7%B3%BB%E7%BB%9F">类加载系统</h1>
<p>Java虚拟机运行你的代码的第一步，就是先加载你的.class文件中的类型信息到内存中。</p>
<ol>
<li>加载(Loading)。由<strong>类加载器(Class Loaders)</strong> 执行，查找字节码，创建一个<code>Class</code>对象。</li>
<li>链接(Linking)。验证字节码，为静态域分配存储空间，如果必需的话，会解析这个类创建的对其他类的所有引用（比如说该类持有<code>static</code>域）。</li>
<li>初始化(Initializing)。如果该类有超类，则对其初始化，执行静态初始化器和静态初始化块。</li>
</ol>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="11" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="11" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E7%B1%BB%E5%8A%A0%E8%BD%BD%E5%99%A8">类加载器</h1>
<p><img src="images/4/jvmblock.gif" alt="" style="height:350px;" /></p>
<p>Java类由<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/ClassLoader.html"><code>java.lang.ClassLoader</code></a>加载。<br />
那问题来了，<code>java.lang.ClassLoader</code>本身也是个类，谁负责加载它?</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="12" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="12" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="bootstrap-class-loader">Bootstrap Class Loader</h1>
<p><strong>Bootstrap Class Loader</strong> is mainly responsible for loading JDK internal classes, typically <code>rt.jar</code> and other core libraries located in <code>$JAVA_HOME/jre/lib</code> directory.</p>
<p>This bootstrap class loader is part of the core JVM and is written in native code as pointed out in the above example. Different platforms might have different implementations of this particular class loader.</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="13" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="13" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E6%AD%A4%E5%A4%96">此外</h1>
<p>The <strong>extension class loader</strong> takes care of loading the extensions of the standard core Java classes so that it's available to all applications running on the platform. It loads from the JDK extensions directory, usually <code>$JAVA_HOME/lib/ext</code> directory or any other directory mentioned in the <code>java.ext.dirs</code> system property.</p>
<p>The <strong>system or application class loader</strong> takes care of loading all the application level classes into the JVM. It loads files found in the classpath environment variable, <code>-classpath</code> or <code>-cp</code> command line option.</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="14" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="14" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h4 id="try">Try</h4>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">import</span> java.util.ArrayList;
<span class="hljs-keyword">import</span> java.sql.Array;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">PrintClassLoader</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] ags)</span> {
System.out.println(<span class="hljs-string">"Classloader of this class:"</span> + PrintClassLoader.class.getClassLoader());
System.out.println(<span class="hljs-string">"Classloader of Array:"</span> + Array.class.getClassLoader());
System.out.println(<span class="hljs-string">"Classloader of ArrayList:"</span> + ArrayList.class.getClassLoader());
}
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-sh">Classloader of this class:jdk.internal.loader.ClassLoaders<span class="hljs-variable">$AppClassLoader</span>@55054057
Classloader of Array:jdk.internal.loader.ClassLoaders<span class="hljs-variable">$PlatformClassLoader</span>@2626b418
Classloader of ArrayList:null
</code></pre>
<div style="text-align:center; color:red">注：Java 9以后Extension class loader改为Platform class loader。</div>
<div style="text-align:center; color:red">请问： 输出中 $ 代表什么？</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="15" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="15" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E7%B1%BB%E5%8A%A0%E8%BD%BD%E5%99%A8%E5%A6%82%E4%BD%95%E5%B7%A5%E4%BD%9C">类加载器如何工作?</h1>
<p><img src="images/4/loading.webp" alt="" style="height:520px;" /></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="16" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="16" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h3 id="%E6%96%87%E5%AD%97%E7%89%88%E6%9C%AC">文字版本</h3>
<ul>
<li>When the JVM requests a class, the class loader tries to locate the class and load the class definition into the runtime using the fully qualified class name.</li>
<li>The <code>java.lang.ClassLoader.loadClass()</code> method is responsible for loading the class definition into runtime.</li>
<li>If the class isn't already loaded, it delegates the request to the <strong>parent class loader</strong>. This process happens recursively.</li>
<li>If the parent class loader doesn’t find the class, then the child class will try to look for classes in the file system itself.</li>
<li>If unsucessful, it throws exception/error.</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="17" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="17" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="when-the-jvm-requests-a-class">When the JVM requests a class?</h1>
<ul>
<li><code>new</code>一个类型的对象</li>
<li><code>java.lang.Class.forName()</code></li>
</ul>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code>
public static Class<?> forName(String className)
throws ClassNotFoundException
public static Class<?> forName(String name, boolean initialize, ClassLoader loader)
throws ClassNotFoundException
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="18" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="18" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="delegation-model">Delegation Model</h1>
<ul>
<li>
<p>Class loaders follow the delegation model where on request to find a class or resource, a ClassLoader instance will delegate the search of the class or resource to the parent class loader.</p>
</li>
<li>
<p>The system class loader first delegates the loading of that class to its parent extension class loader which in turn delegates it to the bootstrap class loader.</p>
</li>
<li>
<p>Only if the bootstrap and then the extension class loader is unsuccessful in loading the class, the system class loader tries to load the class itself.</p>
</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="19" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="19" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="unique-classes">Unique Classes</h1>
<p>As a consequence of the delegation model, it's easy to ensure unique classes as we always try to delegate upwards.</p>
<p>If the parent class loader isn't able to find the class, only then the current instance would attempt to do so itself.</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="20" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="20" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="visibility">Visibility</h1>
<p>In addition, children class loaders are visible to classes loaded by its parent class loaders.</p>
<p>For instance, classes loaded by the system class loader have visibility into classes loaded by the extension and Bootstrap class loaders but not vice-versa.</p>
<br />
<div style="text-align:center; color:red">所以你不能写个恶意的String类型替换掉系统内部的String</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="21" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="21" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h4 id="%E8%87%AA%E5%AE%9A%E4%B9%89%E7%B1%BB%E5%8A%A0%E8%BD%BD%E5%99%A8">自定义类加载器</h4>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">CustomClassLoader</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">ClassLoader</span> {
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> Class <span class="hljs-title function_">findClass</span><span class="hljs-params">(String name)</span> <span class="hljs-keyword">throws</span> ClassNotFoundException {
<span class="hljs-type">byte</span>[] b = loadClassFromFile(name);
<span class="hljs-keyword">return</span> defineClass(name, b, <span class="hljs-number">0</span>, b.length);
}
<span class="hljs-keyword">private</span> <span class="hljs-type">byte</span>[] loadClassFromFile(String fileName) {
<span class="hljs-type">InputStream</span> <span class="hljs-variable">inputStream</span> <span class="hljs-operator">=</span> getClass().getClassLoader().getResourceAsStream(
fileName.replace(<span class="hljs-string">'.'</span>, File.separatorChar) + <span class="hljs-string">".class"</span>);
<span class="hljs-type">byte</span>[] buffer;
<span class="hljs-type">ByteArrayOutputStream</span> <span class="hljs-variable">byteStream</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">ByteArrayOutputStream</span>();
<span class="hljs-type">int</span> <span class="hljs-variable">nextValue</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">while</span> ( (nextValue = inputStream.read()) != -<span class="hljs-number">1</span> ) {
byteStream.write(nextValue);
}
} <span class="hljs-keyword">catch</span> (IOException e) {
e.printStackTrace();
}
buffer = byteStream.toByteArray();
<span class="hljs-keyword">return</span> buffer;
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="22" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="22" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E6%9C%89%E5%95%A5%E7%94%A8">有啥用</h1>
<p>Browsers, for instance, use a custom class loader to load executable content from a website. A browser can load applets from different web pages using separate class loaders. The applet viewer which is used to run applets contains a ClassLoader that accesses a website on a remote server instead of looking in the local file system. And then loads the raw bytecode files via HTTP, and turns them into classes inside the JVM. Even if these applets have the same name, they are considered as different components if loaded by different class loaders.</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="23" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="23" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E6%9B%B4%E9%AB%98%E7%BA%A7%E7%82%B9">更高级点</h1>
<ul>
<li>Helping in modifying the existing bytecode, e.g. weaving agents</li>
<li>Creating classes dynamically suited to the user's needs. e.g in JDBC, switching between different driver implementations is done through dynamic class loading.</li>
<li>Implementing a class versioning mechanism while loading different bytecodes for classes with same names and packages. This can be done either through URL class loader (load jars via URLs) or custom class loaders.</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="24" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="24" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E5%B0%8F%E7%BB%93">小结</h2>
<ul>
<li>所有的类都是在对其第一次使用时，动态加载到JVM中去的</li>
<li>当程序创建第一个对类的静态成员的引用时，JVM会使用类加载器来根据类名查找.class文件</li>
<li>一旦某个类的<code>Class</code>对象被载入内存，它就被用来创建这个类的所有对象</li>
<li>构造器也是类的静态方法，使用<code>new</code>操作符创建新对象会被当作对类的静态成员的引用</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="25" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:55%;" data-marpit-pagination-total="48" data-marpit-advanced-background="background" data-marpit-advanced-background-split="right"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("https://upload.wikimedia.org/wikipedia/commons/d/dd/JvmSpec7.png");background-size:contain;"></figure></div></section></foreignObject><foreignObject width="45%" height="720"><section id="25" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="25" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:55%;" data-marpit-pagination-total="48" data-marpit-advanced-background="content" data-marpit-advanced-background-split="right">
<h1 id="%E8%BF%9B%E5%86%85%E5%AD%98%E5%90%8E%E5%95%A5%E6%A0%B7">进内存后啥样</h1>
<p>The method area stores per-class information</p>
<ul>
<li>Classloader Reference</li>
<li>Run Time Constant Pool</li>
<li>Field data</li>
<li>Method data</li>
<li>Method code</li>
</ul>
</section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="25" style="" data-marpit-pagination-total="48" data-marpit-advanced-background="pseudo" data-marpit-advanced-background-split="right"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="26" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="26" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E4%B8%BE%E4%B8%AA%E4%BE%8B%E5%AD%90">举个例子</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">package</span> org.jvminternals;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SimpleClass</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">sayHello</span><span class="hljs-params">()</span> {
System.out.println(<span class="hljs-string">"Hello"</span>);
}
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-bash">javap -v -p -s -sysinfo -constants SimpleClass.class
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="27" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="27" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E8%BE%93%E5%87%BA">输出</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code>public class org.jvminternals.SimpleClass
SourceFile: "SimpleClass.java"
minor version: 0
major version: 51
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #6.#17 // java/lang/Object."<init>":()V
#2 = Fieldref #18.#19 // java/lang/System.out:Ljava/io/PrintStream;
#3 = String #20 // "Hello"
#4 = Methodref #21.#22 // java/io/PrintStream.println:(Ljava/lang/String;)V
...
#25 = Utf8 java/lang/System
#26 = Utf8 out
#27 = Utf8 Ljava/io/PrintStream;
#28 = Utf8 java/io/PrintStream
#29 = Utf8 println
#30 = Utf8 (Ljava/lang/String;)V
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="28" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="28" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code>{
public org.jvminternals.SimpleClass();
Signature: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 3: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lorg/jvminternals/SimpleClass;
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="29" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="29" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code> public void sayHello();
Signature: ()V
flags: ACC_PUBLIC
Code:
stack=2, locals=1, args_size=1
0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3 // String "Hello"
5: invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
8: return
LineNumberTable:
line 6: 0
line 7: 8
LocalVariableTable:
Start Length Slot Name Signature
0 9 0 this Lorg/jvminternals/SimpleClass;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="30" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="30" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h4 id="%E4%B8%BA%E4%BD%95%E8%AE%B2%E8%BF%99%E4%BA%9B">为何讲这些?</h4>
<blockquote>
<p>If you understand stack very well then you will understand how memory works in program and if you understand how memory works in program you will understand how function store in program and if you understand how function store in program you will understand how recursive function works and if you understand how recursive function works you will understand how compiler works and if you understand how compiler works your mind will works as compiler and you will debug any program very easily.</p>
</blockquote>
<p><small><a href="https://stackoverflow.com/questions/10057443/explain-the-concept-of-a-stack-frame-in-a-nutshell">https://stackoverflow.com/questions/10057443/explain-the-concept-of-a-stack-frame-in-a-nutshell</a></small></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="31" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="31" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E9%98%85%E8%AF%BBjvm-internals">阅读《JVM Internals》</h2>
<p><img src="images/4/JVM_Internal_Architecture_small.png" alt="" style="height:400px;" /></p>
<br />
<div style="text-align:right;font-size:20pt">https://blog.jamesdbloom.com/JVMInternals.html</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="32" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="32" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<p><code>Class.forName(String str)</code></p>
<p><code>Class</code>类的静态方法<code>forName(String str)</code>，可以让我们对于某个类不进行创建就得到它的<code>Class</code>对象的引用</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">try</span> {
<span class="hljs-type">Class</span> <span class="hljs-variable">circleClass</span> <span class="hljs-operator">=</span> Class.forName(<span class="hljs-string">"Circle"</span>);
} <span class="hljs-keyword">catch</span> (ClassNotFoundException e) {
}
</code></pre>
<p>缺点是什么？</p>
<p>可能有异常，且会触发类的static子句（静态初始化块）</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="33" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="33" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E7%B1%BB%E5%AD%97%E9%9D%A2%E5%B8%B8%E9%87%8F-class-literals">类字面常量 Class literals</h2>
<p>Class literals also provide a reference to the Class object</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-type">Class</span> <span class="hljs-variable">c</span> <span class="hljs-operator">=</span> Circle.class;
</code></pre>
<p>支持编译时检查，所以不会抛出异常;不会触发类的static子句（静态初始化块）</p>
<p>更简单更安全更高效</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="34" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="34" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E5%9F%BA%E6%9C%AC%E7%B1%BB%E5%9E%8B%E7%9A%84class%E5%AF%B9%E8%B1%A1">基本类型的Class对象</h2>
<p>Each object of a primitive wrapper class has a standard field called TYPE that also provides a reference to the Class object</p>
<p><small><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html#TYPE">https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html#TYPE</a></small></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="35" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="35" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E7%B1%BB%E5%9E%8B%E6%A3%80%E6%9F%A5">类型检查</h2>
<p><code>public boolean isInstance(Object obj)</code></p>
<blockquote>
<p>Determines if the specified Object is assignment-compatible with the object represented by this Class.</p>
</blockquote>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">if</span> ( Shape.class.isInstance(x) ) {
<span class="hljs-type">Shape</span> <span class="hljs-variable">s</span> <span class="hljs-operator">=</span> (Shape)x;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="36" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="36" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E6%88%96%E8%80%85">或者</h2>
<p>也可以使用<code>instanceof</code>关键字进行类型检查</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">if</span> ( x <span class="hljs-keyword">instanceof</span> Shape ) {
<span class="hljs-type">Shape</span> <span class="hljs-variable">s</span> <span class="hljs-operator">=</span> (Shape)x;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="37" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="37" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E4%BB%8Eclass%E5%AF%B9%E8%B1%A1%E5%88%9B%E5%BB%BA%08%E5%AF%B9%E8%B1%A1">从Class对象创建对象</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">try</span> {
Class<?> circleClass = Class.forName(<span class="hljs-string">"Circle"</span>);
<span class="hljs-type">Object</span> <span class="hljs-variable">obj</span> <span class="hljs-operator">=</span> circleClass.newInstance();
} <span class="hljs-keyword">catch</span> (ClassNotFoundException e) {
}
<span class="hljs-comment">//or </span>
Class<?> circleClass = Circle.class;
<span class="hljs-type">Object</span> <span class="hljs-variable">obj</span> <span class="hljs-operator">=</span> circleClass.newInstance();
</code></pre>
<p>只能得到Object类型... <?>又是什么鬼？</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="38" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="38" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="%E5%88%9B%E5%BB%BA%E5%87%BA%E5%AE%9E%E9%99%85%E7%B1%BB%E5%9E%8B%E7%9A%84%E5%AF%B9%E8%B1%A1">创建出实际类型的对象</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java">Class<Circle> circleClass = Circle.class;
<span class="hljs-type">Circle</span> <span class="hljs-variable">obj</span> <span class="hljs-operator">=</span> circleClass.newInstance();
</code></pre>
<p>Class<Circle> → 范型（generic type）下次再说</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="39" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="39" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E8%87%AA%E7%9C%81introspection">自省（Introspection）</h1>
<p>自省 Introspection： 自我评价、自我反省、自我批评、自我调控和自我教育</p>
<p>In computing, type introspection is the ability of a program to examine the type or properties of an object at runtime.</p>
<div style="text-align:right">-- Wikipedia</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="40" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="40" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="reflection">Reflection</h1>
<p>In computer science, reflection is the ability of a computer program to examine, introspect, and modify its own structure and behavior at runtime.</p>
<div style="text-align:right">-- Wikipedia</div>
<p>Introspection是Reflection的子集。反射除了检查，还可以控制改变。</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="41" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:50%;" data-marpit-pagination-total="48" data-marpit-advanced-background="background" data-marpit-advanced-background-split="right"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("images/4/kongzi.jpg");background-size:contain;"></figure></div></section></foreignObject><foreignObject width="50%" height="720"><section id="41" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="41" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:50%;" data-marpit-pagination-total="48" data-marpit-advanced-background="content" data-marpit-advanced-background-split="right">
<h2 id="%E5%AD%90%E6%9B%B0">子曰</h2>
<p><br /><br /><br />
<br /><br />
<br /></p>
<blockquote>
<p>见贤思齐焉，见不贤而内自省也</p>
</blockquote>
</section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="41" style="" data-marpit-pagination-total="48" data-marpit-advanced-background="pseudo" data-marpit-advanced-background-split="right"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="42" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48" data-marpit-advanced-background="background"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("images/4/zengzi.jpg");"></figure></div></section></foreignObject><foreignObject width="1280" height="720"><section id="42" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="42" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48" data-marpit-advanced-background="content"></section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="42" style="" data-marpit-pagination-total="48" data-marpit-advanced-background="pseudo"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="43" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="43" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="java-reflection">Java Reflection</h2>
<p>Java supports introspection through its <a href="https://www.oracle.com/technetwork/articles/java/javareflection-1536171.html">reflection library</a>.</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">import</span> java.lang.reflect.*;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">DumpMethods</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String args[])</span> {
<span class="hljs-keyword">try</span> {
<span class="hljs-type">Class</span> <span class="hljs-variable">c</span> <span class="hljs-operator">=</span> Class.forName(args[<span class="hljs-number">0</span>]);
Method m[] = c.getDeclaredMethods();
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < m.length; i++)
System.out.println(m[i].toString());
}
<span class="hljs-keyword">catch</span> (Throwable e) {
System.err.println(e);
}
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="44" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="44" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="java-reflection-1">Java Reflection</h1>
<p>Reflection enables Java code to discover information about the fields, methods and constructors of loaded classes, and to use reflected fields, methods, and constructors to operate on their underlying counterparts, within security restrictions. The API accommodates applications that need access to either the public members of a target object (based on its runtime class) or the members declared by a given class. It also allows programs to suppress default reflective access control.</p>
<p><small><a href="https://docs.oracle.com/javase/8/docs/technotes/guides/reflection/index.html">https://docs.oracle.com/javase/8/docs/technotes/guides/reflection/index.html</a></small></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="45" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="45" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E6%A0%B8%E5%BF%83%E5%8A%9F%E8%83%BD">核心功能</h1>
<p>反射的核心是 JVM 在运行时才动态加载类或调用方法/访问属性，它不需要事先（写代码的时候或编译期）知道运行对象是谁。</p>
<ul>
<li>在运行时判断任意一个对象所属的类；</li>
<li>在运行时构造任意一个类的对象；</li>
<li>在运行时判断任意一个类所具有的成员变量和方法</li>
<li>在运行时调用任意一个对象的方法</li>
</ul>
<div style="text-align:right;color:red">重点：是运行时而不是编译时</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="46" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="46" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h1 id="%E6%9C%89%E5%95%A5%E7%94%A8-1">有啥用</h1>
<ul>
<li>Rapid Application Development (RAD)</li>
<li>Visual approach to GUI development</li>
<li>Requires information about component at run-time</li>
<li>Remote Method Invocation (RMI)</li>
<li>Distributed objects</li>
</ul>
<p>当我们在使用 IDE(如 Eclipse，IDEA)时，当我们输入一个对象或类并想调用它的属性或方法时，一按点号，编译器就会自动列出它的属性或方法，这里就会用到反射。 更重要的用途就是<span style="color:red">开发各种通用框架<span>。</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="47" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="47" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48">
<h2 id="introspection-in-python">Introspection in Python</h2>
<p>The Inspect module provides introspections mechanism</p>
<p><a href="https://docs.python.org/3/library/inspect.html">https://docs.python.org/3/library/inspect.html</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="48" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48" data-marpit-advanced-background="background"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("images/happy.png");background-size:50%;"></figure></div></section></foreignObject><foreignObject width="1280" height="720"><section id="48" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="48" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="48" data-marpit-advanced-background="content"></section>
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</script></foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="zh-CN" data-marpit-pagination="48" style="" data-marpit-pagination-total="48" data-marpit-advanced-background="pseudo"></section></foreignObject></svg></div><div class="bespoke-marp-note" data-index="30" tabindex="0"><p></p></div><div class="bespoke-marp-note" data-index="38" tabindex="0"><p>## 问题
以上使用的RTTI都具有一个共同的限制：在编译时，编译器必须知道所有要通过RTTI来处理的类。
但有的时候，你获取了一个对象引用，然而其对应的类并不在你的程序空间中，怎么办？比如说你从磁盘文件或者网络中获取了一串字串，并且被告知这一串字串代表了一个类，这个类在编译器为你的程序生成代码之后才会出现。
---</p></div><script>/*!! License: https://unpkg.com/@marp-team/[email protected]/lib/bespoke.js.LICENSE.txt */
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