Runtime.java

/*
 * Copyright (c) 1995, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import java.io.File;
import java.io.IOException;
import java.math.BigInteger;
import java.util.List;
import java.util.Optional;
import java.util.StringTokenizer;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;

/**
 * Every Java application has a single instance of class
 * {@code Runtime} that allows the application to interface with
 * the environment in which the application is running. The current
 * runtime can be obtained from the {@code getRuntime} method.
 * <p>
 * An application cannot create its own instance of this class.
 *
 * @author unascribed
 * @see java.lang.Runtime#getRuntime()
 * @since 1.0
 */
// 运行时对象，持有一些底层操作工具方法
public class Runtime {
    
    // 单例
    private static final Runtime currentRuntime = new Runtime();
    
    private static Version version; // 当前JDK版本
    
    
    
    /*▼ 构造器/工厂 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /** Don't let anyone else instantiate this class */
    private Runtime() {
    }
    
    /**
     * Returns the runtime object associated with the current Java application.
     * Most of the methods of class {@code Runtime} are instance
     * methods and must be invoked with respect to the current runtime object.
     *
     * @return the {@code Runtime} object associated with the current
     * Java application.
     */
    // 返回Runtime对象(工厂方法)
    public static Runtime getRuntime() {
        return currentRuntime;
    }
    
    /*▲ 构造器/工厂 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 关机回调 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Registers a new virtual-machine shutdown hook.
     *
     * <p> The Java virtual machine <i>shuts down</i> in response to two kinds
     * of events:
     *
     * <ul>
     *
     * <li> The program <i>exits</i> normally, when the last non-daemon
     * thread exits or when the {@link #exit exit} (equivalently,
     * {@link System#exit(int) System.exit}) method is invoked, or
     *
     * <li> The virtual machine is <i>terminated</i> in response to a
     * user interrupt, such as typing {@code ^C}, or a system-wide event,
     * such as user logoff or system shutdown.
     *
     * </ul>
     *
     * <p> A <i>shutdown hook</i> is simply an initialized but unstarted
     * thread.  When the virtual machine begins its shutdown sequence it will
     * start all registered shutdown hooks in some unspecified order and let
     * them run concurrently.  When all the hooks have finished it will then
     * halt. Note that daemon threads will continue to run during the shutdown
     * sequence, as will non-daemon threads if shutdown was initiated by
     * invoking the {@link #exit exit} method.
     *
     * <p> Once the shutdown sequence has begun it can be stopped only by
     * invoking the {@link #halt halt} method, which forcibly
     * terminates the virtual machine.
     *
     * <p> Once the shutdown sequence has begun it is impossible to register a
     * new shutdown hook or de-register a previously-registered hook.
     * Attempting either of these operations will cause an
     * {@link IllegalStateException} to be thrown.
     *
     * <p> Shutdown hooks run at a delicate time in the life cycle of a virtual
     * machine and should therefore be coded defensively.  They should, in
     * particular, be written to be thread-safe and to avoid deadlocks insofar
     * as possible.  They should also not rely blindly upon services that may
     * have registered their own shutdown hooks and therefore may themselves in
     * the process of shutting down.  Attempts to use other thread-based
     * services such as the AWT event-dispatch thread, for example, may lead to
     * deadlocks.
     *
     * <p> Shutdown hooks should also finish their work quickly.  When a
     * program invokes {@link #exit exit} the expectation is
     * that the virtual machine will promptly shut down and exit.  When the
     * virtual machine is terminated due to user logoff or system shutdown the
     * underlying operating system may only allow a fixed amount of time in
     * which to shut down and exit.  It is therefore inadvisable to attempt any
     * user interaction or to perform a long-running computation in a shutdown
     * hook.
     *
     * <p> Uncaught exceptions are handled in shutdown hooks just as in any
     * other thread, by invoking the
     * {@link ThreadGroup#uncaughtException uncaughtException} method of the
     * thread's {@link ThreadGroup} object. The default implementation of this
     * method prints the exception's stack trace to {@link System#err} and
     * terminates the thread; it does not cause the virtual machine to exit or
     * halt.
     *
     * <p> In rare circumstances the virtual machine may <i>abort</i>, that is,
     * stop running without shutting down cleanly.  This occurs when the
     * virtual machine is terminated externally, for example with the
     * {@code SIGKILL} signal on Unix or the {@code TerminateProcess} call on
     * Microsoft Windows.  The virtual machine may also abort if a native
     * method goes awry by, for example, corrupting internal data structures or
     * attempting to access nonexistent memory.  If the virtual machine aborts
     * then no guarantee can be made about whether or not any shutdown hooks
     * will be run.
     *
     * @param hook An initialized but unstarted {@link Thread} object
     *
     * @throws IllegalArgumentException If the specified hook has already been registered,
     *                                  or if it can be determined that the hook is already running or
     *                                  has already been run
     * @throws IllegalStateException    If the virtual machine is already in the process
     *                                  of shutting down
     * @throws SecurityException        If a security manager is present and it denies
     *                                  {@link RuntimePermission}("shutdownHooks")
     * @see #removeShutdownHook
     * @see #halt(int)
     * @see #exit(int)
     * @since 1.3
     */
    /*
     * 在JVM注册一个钩子线程，该线程在以下情形中被执行：
     *
     * 当最后一个非守护程序线程退出；
     * 或调用Runtime#exit方法（与System.exit()等效）；
     * 或被用户中断(^C)；
     * 或被系统自然中断；
     */
    public void addShutdownHook(Thread hook) {
        SecurityManager sm = System.getSecurityManager();
        if(sm != null) {
            sm.checkPermission(new RuntimePermission("shutdownHooks"));
        }
        
        // 注册用户级别的钩子
        ApplicationShutdownHooks.add(hook);
    }
    
    /**
     * De-registers a previously-registered virtual-machine shutdown hook.
     *
     * @param hook the hook to remove
     *
     * @return {@code true} if the specified hook had previously been
     * registered and was successfully de-registered, {@code false}
     * otherwise.
     *
     * @throws IllegalStateException If the virtual machine is already in the process of shutting
     *                               down
     * @throws SecurityException     If a security manager is present and it denies
     *                               {@link RuntimePermission}("shutdownHooks")
     * @see #addShutdownHook
     * @see #exit(int)
     * @since 1.3
     */
    // 移除注册的钩子线程
    public boolean removeShutdownHook(Thread hook) {
        SecurityManager sm = System.getSecurityManager();
        if(sm != null) {
            sm.checkPermission(new RuntimePermission("shutdownHooks"));
        }
        
        // 移除用户级别的钩子
        return ApplicationShutdownHooks.remove(hook);
    }
    
    /*▲ 关机回调 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 关机 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Terminates the currently running Java virtual machine by initiating its
     * shutdown sequence.  This method never returns normally.  The argument
     * serves as a status code; by convention, a nonzero status code indicates
     * abnormal termination.
     *
     * <p> All registered {@linkplain #addShutdownHook shutdown hooks}, if any,
     * are started in some unspecified order and allowed to run concurrently
     * until they finish.  Once this is done the virtual machine
     * {@linkplain #halt halts}.
     *
     * <p> If this method is invoked after all shutdown hooks have already
     * been run and the status is nonzero then this method halts the
     * virtual machine with the given status code. Otherwise, this method
     * blocks indefinitely.
     *
     * <p> The {@link System#exit(int) System.exit} method is the
     * conventional and convenient means of invoking this method.
     *
     * @param status Termination status.  By convention, a nonzero status code
     *               indicates abnormal termination.
     *
     * @throws SecurityException If a security manager is present and its
     *                           {@link SecurityManager#checkExit checkExit} method does not permit
     *                           exiting with the specified status
     * @see java.lang.SecurityException
     * @see java.lang.SecurityManager#checkExit(int)
     * @see #addShutdownHook
     * @see #removeShutdownHook
     * @see #halt(int)
     */
    // 执行所有关机回调，并退出(关闭)虚拟机
    public void exit(int status) {
        SecurityManager security = System.getSecurityManager();
        if(security != null) {
            security.checkExit(status);
        }
        
        Shutdown.exit(status);
    }
    
    /**
     * Forcibly terminates the currently running Java virtual machine.  This
     * method never returns normally.
     *
     * <p> This method should be used with extreme caution.  Unlike the
     * {@link #exit exit} method, this method does not cause shutdown
     * hooks to be started.  If the shutdown sequence has already been
     * initiated then this method does not wait for any running
     * shutdown hooks to finish their work.
     *
     * @param status Termination status. By convention, a nonzero status code
     *               indicates abnormal termination. If the {@link Runtime#exit exit}
     *               (equivalently, {@link System#exit(int) System.exit}) method
     *               has already been invoked then this status code
     *               will override the status code passed to that method.
     *
     * @throws SecurityException If a security manager is present and its
     *                           {@link SecurityManager#checkExit checkExit} method
     *                           does not permit an exit with the specified status
     * @see #exit
     * @see #addShutdownHook
     * @see #removeShutdownHook
     * @since 1.3
     */
    /*
     * 直接关闭虚拟机，不会执行关机回调
     *
     * status为关闭时的状态码，一般用非0的状态码表示异常退出状态
     */
    public void halt(int status) {
        SecurityManager sm = System.getSecurityManager();
        if(sm != null) {
            sm.checkExit(status);
        }
        
        // 通知虚拟机程序该终止了
        Shutdown.beforeHalt();
        
        // 关闭虚拟机
        Shutdown.halt(status);
    }
    
    /*▲ 关机 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 进程/命令行 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Executes the specified string command in a separate process.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code exec(command)}
     * behaves in exactly the same way as the invocation
     * {@link #exec(String, String[], File) exec}{@code (command, null, null)}.
     *
     * @param command a specified system command.
     *
     * @return A new {@link Process} object for managing the subprocess
     *
     * @throws SecurityException        If a security manager exists and its
     *                                  {@link SecurityManager#checkExec checkExec}
     *                                  method doesn't allow creation of the subprocess
     * @throws IOException              If an I/O error occurs
     * @throws NullPointerException     If {@code command} is {@code null}
     * @throws IllegalArgumentException If {@code command} is empty
     * @see #exec(String[], String[], File)
     * @see ProcessBuilder
     */
    // 构造执行指定命令的进程
    public Process exec(String command) throws IOException {
        return exec(command, null, null);
    }
    
    /**
     * Executes the specified string command in a separate process with the
     * specified environment.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code exec(command, envp)}
     * behaves in exactly the same way as the invocation
     * {@link #exec(String, String[], File) exec}{@code (command, envp, null)}.
     *
     * @param command a specified system command.
     * @param envp    array of strings, each element of which
     *                has environment variable settings in the format
     *                <i>name</i>=<i>value</i>, or
     *                {@code null} if the subprocess should inherit
     *                the environment of the current process.
     *
     * @return A new {@link Process} object for managing the subprocess
     *
     * @throws SecurityException        If a security manager exists and its
     *                                  {@link SecurityManager#checkExec checkExec}
     *                                  method doesn't allow creation of the subprocess
     * @throws IOException              If an I/O error occurs
     * @throws NullPointerException     If {@code command} is {@code null},
     *                                  or one of the elements of {@code envp} is {@code null}
     * @throws IllegalArgumentException If {@code command} is empty
     * @see #exec(String[], String[], File)
     * @see ProcessBuilder
     */
    // 构造执行指定命令的进程，envp为进程设置环境变量
    public Process exec(String command, String[] envp) throws IOException {
        return exec(command, envp, null);
    }
    
    /**
     * Executes the specified string command in a separate process with the
     * specified environment and working directory.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code exec(command, envp, dir)}
     * behaves in exactly the same way as the invocation
     * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, dir)},
     * where {@code cmdarray} is an array of all the tokens in
     * {@code command}.
     *
     * <p>More precisely, the {@code command} string is broken
     * into tokens using a {@link StringTokenizer} created by the call
     * {@code new {@link StringTokenizer}(command)} with no
     * further modification of the character categories.  The tokens
     * produced by the tokenizer are then placed in the new string
     * array {@code cmdarray}, in the same order.
     *
     * @param command a specified system command.
     * @param envp    array of strings, each element of which
     *                has environment variable settings in the format
     *                <i>name</i>=<i>value</i>, or
     *                {@code null} if the subprocess should inherit
     *                the environment of the current process.
     * @param dir     the working directory of the subprocess, or
     *                {@code null} if the subprocess should inherit
     *                the working directory of the current process.
     *
     * @return A new {@link Process} object for managing the subprocess
     *
     * @throws SecurityException        If a security manager exists and its
     *                                  {@link SecurityManager#checkExec checkExec}
     *                                  method doesn't allow creation of the subprocess
     * @throws IOException              If an I/O error occurs
     * @throws NullPointerException     If {@code command} is {@code null},
     *                                  or one of the elements of {@code envp} is {@code null}
     * @throws IllegalArgumentException If {@code command} is empty
     * @see ProcessBuilder
     * @since 1.3
     */
    // 构造执行指定命令的进程，envp为进程设置环境变量，dir为进程设置工作目录
    public Process exec(String command, String[] envp, File dir) throws IOException {
        if(command.length() == 0) {
            throw new IllegalArgumentException("Empty command");
        }
        
        StringTokenizer st = new StringTokenizer(command);
        String[] cmdarray = new String[st.countTokens()];
        for(int i = 0; st.hasMoreTokens(); i++) {
            cmdarray[i] = st.nextToken();
        }
        
        return exec(cmdarray, envp, dir);
    }
    
    /**
     * Executes the specified command and arguments in a separate process.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code exec(cmdarray)}
     * behaves in exactly the same way as the invocation
     * {@link #exec(String[], String[], File) exec}{@code (cmdarray, null, null)}.
     *
     * @param cmdarray array containing the command to call and
     *                 its arguments.
     *
     * @return A new {@link Process} object for managing the subprocess
     *
     * @throws SecurityException         If a security manager exists and its
     *                                   {@link SecurityManager#checkExec checkExec}
     *                                   method doesn't allow creation of the subprocess
     * @throws IOException               If an I/O error occurs
     * @throws NullPointerException      If {@code cmdarray} is {@code null},
     *                                   or one of the elements of {@code cmdarray} is {@code null}
     * @throws IndexOutOfBoundsException If {@code cmdarray} is an empty array
     *                                   (has length {@code 0})
     * @see ProcessBuilder
     */
    // 构造执行指定命令的进程，命令行以数组cmdarray形式给出
    public Process exec(String cmdarray[]) throws IOException {
        return exec(cmdarray, null, null);
    }
    
    /**
     * Executes the specified command and arguments in a separate process
     * with the specified environment.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code exec(cmdarray, envp)}
     * behaves in exactly the same way as the invocation
     * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, null)}.
     *
     * @param cmdarray array containing the command to call and
     *                 its arguments.
     * @param envp     array of strings, each element of which
     *                 has environment variable settings in the format
     *                 <i>name</i>=<i>value</i>, or
     *                 {@code null} if the subprocess should inherit
     *                 the environment of the current process.
     *
     * @return A new {@link Process} object for managing the subprocess
     *
     * @throws SecurityException         If a security manager exists and its
     *                                   {@link SecurityManager#checkExec checkExec}
     *                                   method doesn't allow creation of the subprocess
     * @throws IOException               If an I/O error occurs
     * @throws NullPointerException      If {@code cmdarray} is {@code null},
     *                                   or one of the elements of {@code cmdarray} is {@code null},
     *                                   or one of the elements of {@code envp} is {@code null}
     * @throws IndexOutOfBoundsException If {@code cmdarray} is an empty array
     *                                   (has length {@code 0})
     * @see ProcessBuilder
     */
    // 构造执行指定命令的进程，命令行以数组cmdarray形式给出，envp为进程设置环境变量
    public Process exec(String[] cmdarray, String[] envp) throws IOException {
        return exec(cmdarray, envp, null);
    }
    
    /**
     * Executes the specified command and arguments in a separate process with
     * the specified environment and working directory.
     *
     * <p>Given an array of strings {@code cmdarray}, representing the
     * tokens of a command line, and an array of strings {@code envp},
     * representing "environment" variable settings, this method creates
     * a new process in which to execute the specified command.
     *
     * <p>This method checks that {@code cmdarray} is a valid operating
     * system command.  Which commands are valid is system-dependent,
     * but at the very least the command must be a non-empty list of
     * non-null strings.
     *
     * <p>If {@code envp} is {@code null}, the subprocess inherits the
     * environment settings of the current process.
     *
     * <p>A minimal set of system dependent environment variables may
     * be required to start a process on some operating systems.
     * As a result, the subprocess may inherit additional environment variable
     * settings beyond those in the specified environment.
     *
     * <p>{@link ProcessBuilder#start()} is now the preferred way to
     * start a process with a modified environment.
     *
     * <p>The working directory of the new subprocess is specified by {@code dir}.
     * If {@code dir} is {@code null}, the subprocess inherits the
     * current working directory of the current process.
     *
     * <p>If a security manager exists, its
     * {@link SecurityManager#checkExec checkExec}
     * method is invoked with the first component of the array
     * {@code cmdarray} as its argument. This may result in a
     * {@link SecurityException} being thrown.
     *
     * <p>Starting an operating system process is highly system-dependent.
     * Among the many things that can go wrong are:
     * <ul>
     * <li>The operating system program file was not found.
     * <li>Access to the program file was denied.
     * <li>The working directory does not exist.
     * </ul>
     *
     * <p>In such cases an exception will be thrown.  The exact nature
     * of the exception is system-dependent, but it will always be a
     * subclass of {@link IOException}.
     *
     * <p>If the operating system does not support the creation of
     * processes, an {@link UnsupportedOperationException} will be thrown.
     *
     * @param cmdarray array containing the command to call and
     *                 its arguments.
     * @param envp     array of strings, each element of which
     *                 has environment variable settings in the format
     *                 <i>name</i>=<i>value</i>, or
     *                 {@code null} if the subprocess should inherit
     *                 the environment of the current process.
     * @param dir      the working directory of the subprocess, or
     *                 {@code null} if the subprocess should inherit
     *                 the working directory of the current process.
     *
     * @return A new {@link Process} object for managing the subprocess
     *
     * @throws SecurityException             If a security manager exists and its
     *                                       {@link SecurityManager#checkExec checkExec}
     *                                       method doesn't allow creation of the subprocess
     * @throws UnsupportedOperationException If the operating system does not support the creation of processes.
     * @throws IOException                   If an I/O error occurs
     * @throws NullPointerException          If {@code cmdarray} is {@code null},
     *                                       or one of the elements of {@code cmdarray} is {@code null},
     *                                       or one of the elements of {@code envp} is {@code null}
     * @throws IndexOutOfBoundsException     If {@code cmdarray} is an empty array
     *                                       (has length {@code 0})
     * @see ProcessBuilder
     * @since 1.3
     */
    // 构造执行指定命令的进程，命令行以数组cmdarray形式给出，envp为进程设置环境变量，dir为进程设置工作目录
    public Process exec(String[] cmdarray, String[] envp, File dir) throws IOException {
        return new ProcessBuilder(cmdarray).environment(envp)  // 为进程构造器设置环境变量
            .directory(dir)     // 为进程构造器设定工作目录
            .start();
    }
    
    /*▲ 进程/命令行 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 清理 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Runs the garbage collector.
     * Calling this method suggests that the Java virtual machine expend
     * effort toward recycling unused objects in order to make the memory
     * they currently occupy available for quick reuse. When control
     * returns from the method call, the virtual machine has made
     * its best effort to recycle all discarded objects.
     * <p>
     * The name {@code gc} stands for "garbage
     * collector". The virtual machine performs this recycling
     * process automatically as needed, in a separate thread, even if the
     * {@code gc} method is not invoked explicitly.
     * <p>
     * The method {@link System#gc()} is the conventional and convenient
     * means of invoking this method.
     */
    // 通知虚拟机执行垃圾回收操作
    public native void gc();
    
    /**
     * Runs the finalization methods of any objects pending finalization.
     * Calling this method suggests that the Java virtual machine expend
     * effort toward running the {@code finalize} methods of objects
     * that have been found to be discarded but whose {@code finalize}
     * methods have not yet been run. When control returns from the
     * method call, the virtual machine has made a best effort to
     * complete all outstanding finalizations.
     * <p>
     * The virtual machine performs the finalization process
     * automatically as needed, in a separate thread, if the
     * {@code runFinalization} method is not invoked explicitly.
     * <p>
     * The method {@link System#runFinalization()} is the conventional
     * and convenient means of invoking this method.
     *
     * @see java.lang.Object#finalize()
     */
    // 手动触发Finalizer的清理操作，不用等待FinalizerThread
    public void runFinalization() {
        SharedSecrets.getJavaLangRefAccess().runFinalization();
    }
    
    /*▲ 清理 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 信息 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the maximum amount of memory that the Java virtual machine will attempt to use.
     * If there is no inherent limit then the value {@link java.lang.Long#MAX_VALUE} will be returned.
     *
     * @return the maximum amount of memory that the virtual machine will attempt to use, measured in bytes
     *
     * @since 1.4
     */
    /*
     * 返回虚拟机可用内存的上限(字节数)，可通过-Xmx设置
     *
     * max >= total >= free
     */
    public native long maxMemory();
    
    /**
     * Returns the total amount of memory in the Java virtual machine.
     * The value returned by this method may vary over time, depending on the host environment.
     * <p>
     * Note that the amount of memory required to hold an object of any given type may be implementation-dependent.
     *
     * @return the total amount of memory currently available for current and future objects, measured in bytes.
     */
    /*
     * 返回虚拟机当前可用的最大内存(字节数)，会动态增长或减少，初始值可通过-Xms设置
     *
     * max >= total >= free
     */
    public native long totalMemory();
    
    /**
     * Returns the amount of free memory in the Java Virtual Machine.
     * Calling the {@code gc} method may result in increasing the value returned by {@code freeMemory.}
     *
     * @return an approximation to the total amount of memory currently available for future allocated objects, measured in bytes.
     */
    /*
     * 返回虚拟机当前未使用的内存(字节数)，会动态变化；
     * freeMemory的上限是totalMemory，而totalMemory的上限是maxMemory。
     *
     * max >= total >= free
     */
    public native long freeMemory();
    
    
    /**
     * Returns the number of processors available to the Java virtual machine.
     *
     * <p> This value may change during a particular invocation of the virtual
     * machine.  Applications that are sensitive to the number of available
     * processors should therefore occasionally poll this property and adjust
     * their resource usage appropriately. </p>
     *
     * @return the maximum number of processors available to the virtual
     * machine; never smaller than one
     *
     * @since 1.4
     */
    // 返回虚拟机可用的处理器数量
    public native int availableProcessors();
    
    
    /**
     * Returns the version of the Java Runtime Environment as a {@link Version}.
     *
     * @return the {@link Version} of the Java Runtime Environment
     *
     * @since 9
     */
    // 返回当前JDK版本信息
    public static Version version() {
        if(version == null) {
            version = new Version(VersionProps.versionNumbers(), VersionProps.pre(), VersionProps.build(), VersionProps.optional());
        }
        
        return version;
    }
    
    /*▲ 信息 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 本地库 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Loads the native library specified by the filename argument.  The filename
     * argument must be an absolute path name.
     * (for example
     * {@code Runtime.getRuntime().load("/home/avh/lib/libX11.so");}).
     *
     * If the filename argument, when stripped of any platform-specific library
     * prefix, path, and file extension, indicates a library whose name is,
     * for example, L, and a native library called L is statically linked
     * with the VM, then the JNI_OnLoad_L function exported by the library
     * is invoked rather than attempting to load a dynamic library.
     * A filename matching the argument does not have to exist in the file
     * system.
     * See the <a href="{@docRoot}/../specs/jni/index.html"> JNI Specification</a>
     * for more details.
     *
     * Otherwise, the filename argument is mapped to a native library image in
     * an implementation-dependent manner.
     * <p>
     * First, if there is a security manager, its {@code checkLink}
     * method is called with the {@code filename} as its argument.
     * This may result in a security exception.
     * <p>
     * This is similar to the method {@link #loadLibrary(String)}, but it
     * accepts a general file name as an argument rather than just a library
     * name, allowing any file of native code to be loaded.
     * <p>
     * The method {@link System#load(String)} is the conventional and
     * convenient means of invoking this method.
     *
     * @param filename the file to load.
     *
     * @throws SecurityException    if a security manager exists and its
     *                              {@code checkLink} method doesn't allow
     *                              loading of the specified dynamic library
     * @throws UnsatisfiedLinkError if either the filename is not an
     *                              absolute path name, the native library is not statically
     *                              linked with the VM, or the library cannot be mapped to
     *                              a native library image by the host system.
     * @throws NullPointerException if {@code filename} is
     *                              {@code null}
     * @see java.lang.Runtime#getRuntime()
     * @see java.lang.SecurityException
     * @see java.lang.SecurityManager#checkLink(java.lang.String)
     */
    /*
     * 加载指定名称的本地库(要求filename是本地库的绝对路径)
     * 发起加载操作的是load()方法的调用者所处的类(忽略反射栈帧)
     */
    @CallerSensitive
    public void load(String filename) {
        load0(Reflection.getCallerClass(), filename);
    }
    
    /**
     * Loads the native library specified by the {@code libname}
     * argument.  The {@code libname} argument must not contain any platform
     * specific prefix, file extension or path. If a native library
     * called {@code libname} is statically linked with the VM, then the
     * JNI_OnLoad_{@code libname} function exported by the library is invoked.
     * See the <a href="{@docRoot}/../specs/jni/index.html"> JNI Specification</a>
     * for more details.
     *
     * Otherwise, the libname argument is loaded from a system library
     * location and mapped to a native library image in an implementation-
     * dependent manner.
     * <p>
     * First, if there is a security manager, its {@code checkLink}
     * method is called with the {@code libname} as its argument.
     * This may result in a security exception.
     * <p>
     * The method {@link System#loadLibrary(String)} is the conventional
     * and convenient means of invoking this method. If native
     * methods are to be used in the implementation of a class, a standard
     * strategy is to put the native code in a library file (call it
     * {@code LibFile}) and then to put a static initializer:
     * <blockquote><pre>
     * static { System.loadLibrary("LibFile"); }
     * </pre></blockquote>
     * within the class declaration. When the class is loaded and
     * initialized, the necessary native code implementation for the native
     * methods will then be loaded as well.
     * <p>
     * If this method is called more than once with the same library
     * name, the second and subsequent calls are ignored.
     *
     * @param libname the name of the library.
     *
     * @throws SecurityException    if a security manager exists and its
     *                              {@code checkLink} method doesn't allow
     *                              loading of the specified dynamic library
     * @throws UnsatisfiedLinkError if either the libname argument
     *                              contains a file path, the native library is not statically
     *                              linked with the VM,  or the library cannot be mapped to a
     *                              native library image by the host system.
     * @throws NullPointerException if {@code libname} is
     *                              {@code null}
     * @see java.lang.SecurityException
     * @see java.lang.SecurityManager#checkLink(java.lang.String)
     */
    /*
     * 加载指定名称的本地库，如"net"是指本地网络库
     * 发起加载操作的是loadLibrary()方法的调用者所处的类(忽略反射栈帧)
     */
    @CallerSensitive
    public void loadLibrary(String libname) {
        loadLibrary0(Reflection.getCallerClass(), libname);
    }
    
    // 加载指定名称的本地库(要求filename是本地库的绝对路径)
    synchronized void load0(Class<?> fromClass, String filename) {
        SecurityManager security = System.getSecurityManager();
        if(security != null) {
            security.checkLink(filename);
        }
        
        // 如果filename不是绝对路径，则抛异常
        if(!(new File(filename).isAbsolute())) {
            throw new UnsatisfiedLinkError("Expecting an absolute path of the library: " + filename);
        }
        
        // 加载指定名称的本地库
        ClassLoader.loadLibrary(fromClass, filename, true);
    }
    
    // 加载指定名称的本地库，如"net"是指本地网络库
    synchronized void loadLibrary0(Class<?> fromClass, String libname) {
        SecurityManager security = System.getSecurityManager();
        if(security != null) {
            security.checkLink(libname);
        }
        
        // 如果libname包含路径内部的分隔符，则抛异常
        if(libname.indexOf((int) File.separatorChar) != -1) {
            throw new UnsatisfiedLinkError("Directory separator should not appear in library name: " + libname);
        }
        
        // 加载指定名称的本地库
        ClassLoader.loadLibrary(fromClass, libname, false);
    }
    
    /*▲ 本地库 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 杂项 ███████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Not implemented, does nothing.
     *
     * @param on ignored
     *
     * @deprecated This method was intended to control instruction tracing.
     * It has been superseded by JVM-specific tracing mechanisms.
     * This method is subject to removal in a future version of Java SE.
     */
    @Deprecated(since = "9", forRemoval = true)
    public void traceInstructions(boolean on) {
    }
    
    /**
     * Not implemented, does nothing.
     *
     * @param on ignored
     *
     * @deprecated This method was intended to control method call tracing.
     * It has been superseded by JVM-specific tracing mechanisms.
     * This method is subject to removal in a future version of Java SE.
     */
    @Deprecated(since = "9", forRemoval = true)
    public void traceMethodCalls(boolean on) {
    }
    
    /*▲ 杂项 ███████████████████████████████████████████████████████████████████████████████┛ */
    
    
    // 版本号正则
    private static class VersionPattern {
        // $VNUM(-$PRE)?(\+($BUILD)?(\-$OPT)?)?
        // RE limits the format of version strings
        // ([1-9][0-9]*(?:(?:\.0)*\.[1-9][0-9]*)*)(?:-([a-zA-Z0-9]+))?(?:(\+)(0|[1-9][0-9]*)?)?(?:-([-a-zA-Z0-9.]+))?
        
        static final String VNUM_GROUP = "VNUM";
        static final String PRE_GROUP = "PRE";
        static final String PLUS_GROUP = "PLUS";
        static final String BUILD_GROUP = "BUILD";
        static final String OPT_GROUP = "OPT";
        
        private static final String VNUM = "(?<VNUM>[1-9][0-9]*(?:(?:\\.0)*\\.[1-9][0-9]*)*)";
        private static final String PRE = "(?:-(?<PRE>[a-zA-Z0-9]+))?";
        private static final String BUILD = "(?:(?<PLUS>\\+)(?<BUILD>0|[1-9][0-9]*)?)?";
        private static final String OPT = "(?:-(?<OPT>[-a-zA-Z0-9.]+))?";
        private static final String VSTR_FORMAT = VNUM + PRE + BUILD + OPT;
        
        static final Pattern VSTR_PATTERN = Pattern.compile(VSTR_FORMAT);
    }
    
    /**
     * A representation of a version string for an implementation of the
     * Java&nbsp;SE Platform.  A version string consists of a version number
     * optionally followed by pre-release and build information.
     *
     * <h2><a id="verNum">Version numbers</a></h2>
     *
     * <p> A <em>version number</em>, {@code $VNUM}, is a non-empty sequence of
     * elements separated by period characters (U+002E).  An element is either
     * zero, or an unsigned integer numeral without leading zeros.  The final
     * element in a version number must not be zero.  When an element is
     * incremented, all subsequent elements are removed.  The format is: </p>
     *
     * <blockquote><pre>
     * [1-9][0-9]*((\.0)*\.[1-9][0-9]*)*
     * </pre></blockquote>
     *
     * <p> The sequence may be of arbitrary length but the first four elements
     * are assigned specific meanings, as follows:</p>
     *
     * <blockquote><pre>
     * $FEATURE.$INTERIM.$UPDATE.$PATCH
     * </pre></blockquote>
     *
     * <ul>
     *
     * <li><p> <a id="FEATURE">{@code $FEATURE}</a> &#x2014; The
     * feature-release counter, incremented for every feature release
     * regardless of release content.  Features may be added in a feature
     * release; they may also be removed, if advance notice was given at least
     * one feature release ahead of time.  Incompatible changes may be made
     * when justified. </p></li>
     *
     * <li><p> <a id="INTERIM">{@code $INTERIM}</a> &#x2014; The
     * interim-release counter, incremented for non-feature releases that
     * contain compatible bug fixes and enhancements but no incompatible
     * changes, no feature removals, and no changes to standard APIs.
     * </p></li>
     *
     * <li><p> <a id="UPDATE">{@code $UPDATE}</a> &#x2014; The update-release
     * counter, incremented for compatible update releases that fix security
     * issues, regressions, and bugs in newer features. </p></li>
     *
     * <li><p> <a id="PATCH">{@code $PATCH}</a> &#x2014; The emergency
     * patch-release counter, incremented only when it's necessary to produce
     * an emergency release to fix a critical issue. </p></li>
     *
     * </ul>
     *
     * <p> The fifth and later elements of a version number are free for use by
     * platform implementors, to identify implementor-specific patch
     * releases. </p>
     *
     * <p> A version number never has trailing zero elements.  If an element
     * and all those that follow it logically have the value zero then all of
     * them are omitted. </p>
     *
     * <p> The sequence of numerals in a version number is compared to another
     * such sequence in numerical, pointwise fashion; <em>e.g.</em>, {@code
     * 10.0.4} is less than {@code 10.1.2}.  If one sequence is shorter than
     * another then the missing elements of the shorter sequence are considered
     * to be less than the corresponding elements of the longer sequence;
     * <em>e.g.</em>, {@code 10.0.2} is less than {@code 10.0.2.1}. </p>
     *
     * <h2><a id="verStr">Version strings</a></h2>
     *
     * <p> A <em>version string</em>, {@code $VSTR}, is a version number {@code
     * $VNUM}, as described above, optionally followed by pre-release and build
     * information, in one of the following formats: </p>
     *
     * <blockquote><pre>
     *     $VNUM(-$PRE)?\+$BUILD(-$OPT)?
     *     $VNUM-$PRE(-$OPT)?
     *     $VNUM(+-$OPT)?
     * </pre></blockquote>
     *
     * <p> where: </p>
     *
     * <ul>
     *
     * <li><p> <a id="pre">{@code $PRE}</a>, matching {@code ([a-zA-Z0-9]+)}
     * &#x2014; A pre-release identifier.  Typically {@code ea}, for a
     * potentially unstable early-access release under active development, or
     * {@code internal}, for an internal developer build. </p></li>
     *
     * <li><p> <a id="build">{@code $BUILD}</a>, matching {@code
     * (0|[1-9][0-9]*)} &#x2014; The build number, incremented for each promoted
     * build.  {@code $BUILD} is reset to {@code 1} when any portion of {@code
     * $VNUM} is incremented. </p></li>
     *
     * <li><p> <a id="opt">{@code $OPT}</a>, matching {@code ([-a-zA-Z0-9.]+)}
     * &#x2014; Additional build information, if desired.  In the case of an
     * {@code internal} build this will often contain the date and time of the
     * build. </p></li>
     *
     * </ul>
     *
     * <p> A version string {@code 10-ea} matches {@code $VNUM = "10"} and
     * {@code $PRE = "ea"}.  The version string {@code 10+-ea} matches
     * {@code $VNUM = "10"} and {@code $OPT = "ea"}. </p>
     *
     * <p> When comparing two version strings, the value of {@code $OPT}, if
     * present, may or may not be significant depending on the chosen
     * comparison method.  The comparison methods {@link #compareTo(Version)
     * compareTo()} and {@link #compareToIgnoreOptional(Version)
     * compareToIgnoreOptional()} should be used consistently with the
     * corresponding methods {@link #equals(Object) equals()} and {@link
     * #equalsIgnoreOptional(Object) equalsIgnoreOptional()}.  </p>
     *
     * <p> A <em>short version string</em>, {@code $SVSTR}, often useful in
     * less formal contexts, is a version number optionally followed by a
     * pre-release identifier:</p>
     *
     * <blockquote><pre>
     *     $VNUM(-$PRE)?
     * </pre></blockquote>
     *
     * <p>This is a <a href="./doc-files/ValueBased.html">value-based</a>
     * class; use of identity-sensitive operations (including reference equality
     * ({@code ==}), identity hash code, or synchronization) on instances of
     * {@code Version} may have unpredictable results and should be avoided.
     * </p>
     *
     * @since 9
     */
    // JAVA版本信息
    public static final class Version implements Comparable<Version> {
        private final List<Integer> version;        // 版本号
        
        private final Optional<String> pre;         // 预发行信息
        private final Optional<Integer> build;      // 构建信息
        private final Optional<String> optional;    // 附加信息
        
        /*
         * List of version number components passed to this constructor MUST
         * be at least unmodifiable (ideally immutable). In the case on an
         * unmodifiable list, the caller MUST hand the list over to this
         * constructor and never change the underlying list.
         */
        private Version(List<Integer> unmodifiableListOfVersions, Optional<String> pre, Optional<Integer> build, Optional<String> optional) {
            this.version = unmodifiableListOfVersions;
            this.pre = pre;
            this.build = build;
            this.optional = optional;
        }
        
        /**
         * Parses the given string as a valid
         * <a href="#verStr">version string</a> containing a
         * <a href="#verNum">version number</a> followed by pre-release and
         * build information.
         *
         * @param s A string to interpret as a version
         *
         * @return The Version of the given string
         *
         * @throws IllegalArgumentException If the given string cannot be interpreted as a valid version
         * @throws NullPointerException     If the given string is {@code null}
         * @throws NumberFormatException    If an element of the version number or the build number
         *                                  cannot be represented as an {@link Integer}
         */
        // 将给定的字符串解析为有效的版本号
        public static Version parse(String s) {
            if(s == null) {
                throw new NullPointerException();
            }
    
            // Shortcut to avoid initializing VersionPattern when creating feature-version constants during startup
            if(isSimpleNumber(s)) {
                return new Version(List.of(Integer.parseInt(s)), Optional.empty(), Optional.empty(), Optional.empty());
            }
    
            Matcher m = VersionPattern.VSTR_PATTERN.matcher(s);
            if(!m.matches()) {
                throw new IllegalArgumentException("Invalid version string: '" + s + "'");
            }
    
            // $VNUM is a dot-separated list of integers of arbitrary length
            String[] split = m.group(VersionPattern.VNUM_GROUP).split("\\.");
            Integer[] version = new Integer[split.length];
            for(int i = 0; i<split.length; i++) {
                version[i] = Integer.parseInt(split[i]);
            }
    
            Optional<String> pre = Optional.ofNullable(m.group(VersionPattern.PRE_GROUP));
    
            String b = m.group(VersionPattern.BUILD_GROUP);
    
            // $BUILD is an integer
            Optional<Integer> build = (b == null) ? Optional.empty() : Optional.of(Integer.parseInt(b));
    
            Optional<String> optional = Optional.ofNullable(m.group(VersionPattern.OPT_GROUP));
    
            // empty '+'
            if(!build.isPresent()) {
                if(m.group(VersionPattern.PLUS_GROUP) != null) {
                    if(optional.isPresent()) {
                        if(pre.isPresent())
                            throw new IllegalArgumentException("'+' found with" + " pre-release and optional components:'" + s + "'");
                    } else {
                        throw new IllegalArgumentException("'+' found with neither" + " build or optional components: '" + s + "'");
                    }
                } else {
                    if(optional.isPresent() && !pre.isPresent()) {
                        throw new IllegalArgumentException("optional component" + " must be preceeded by a pre-release component" + " or '+': '" + s + "'");
                    }
                }
            }
    
            return new Version(List.of(version), pre, build, optional);
        }
        
        /**
         * Returns the value of the major element of the version number.
         *
         * @return The value of the feature element
         *
         * @deprecated As of Java&nbsp;SE 10, the first element of a version
         * number is not the major-release number but the feature-release
         * counter, incremented for every time-based release.  Use the {@link
         * #feature()} method in preference to this method.  For compatibility,
         * this method returns the value of the <a href="#FEATURE">feature</a>
         * element.
         */
        // 主版本号。已过时，使用"feature"替代
        @Deprecated(since = "10")
        public int major() {
            return feature();
        }
        
        /**
         * Returns the value of the minor element of the version number, or
         * zero if it is absent.
         *
         * @return The value of the interim element, or zero
         *
         * @deprecated As of Java&nbsp;SE 10, the second element of a version
         * number is not the minor-release number but the interim-release
         * counter, incremented for every interim release.  Use the {@link
         * #interim()} method in preference to this method.  For compatibility,
         * this method returns the value of the <a href="#INTERIM">interim</a>
         * element, or zero if it is absent.
         */
        // 次版本号。已过时，使用"interim"替代
        @Deprecated(since = "10")
        public int minor() {
            return interim();
        }
        
        /**
         * Returns the value of the security element of the version number, or
         * zero if it is absent.
         *
         * @return The value of the update element, or zero
         *
         * @deprecated As of Java&nbsp;SE 10, the third element of a version
         * number is not the security level but the update-release counter,
         * incremented for every update release.  Use the {@link #update()}
         * method in preference to this method.  For compatibility, this method
         * returns the value of the <a href="#UPDATE">update</a> element, or
         * zero if it is absent.
         */
        // 安全级别。已过时，使用"update"替代
        @Deprecated(since = "10")
        public int security() {
            return update();
        }
        
        /**
         * Returns an unmodifiable {@link java.util.List List} of the integers
         * represented in the <a href="#verNum">version number</a>.
         * The {@code List} always contains at least one element corresponding to
         * the <a href="#FEATURE">feature version number</a>.
         *
         * @return An unmodifiable list of the integers
         * represented in the version number
         */
        // 返回版本号，由[feature]-[interim]-[update]-[patch]构成
        public List<Integer> version() {
            return version;
        }
        
        /**
         * Returns the value of the <a href="#FEATURE">feature</a> element of
         * the version number.
         *
         * @return The value of the feature element
         *
         * @since 10
         */
        public int feature() {
            return version.get(0);
        }
        
        /**
         * Returns the value of the <a href="#INTERIM">interim</a> element of
         * the version number, or zero if it is absent.
         *
         * @return The value of the interim element, or zero
         *
         * @since 10
         */
        public int interim() {
            return (version.size()>1 ? version.get(1) : 0);
        }
        
        /**
         * Returns the value of the <a href="#UPDATE">update</a> element of the
         * version number, or zero if it is absent.
         *
         * @return The value of the update element, or zero
         *
         * @since 10
         */
        public int update() {
            return (version.size()>2 ? version.get(2) : 0);
        }
        
        /**
         * Returns the value of the <a href="#PATCH">patch</a> element of the
         * version number, or zero if it is absent.
         *
         * @return The value of the patch element, or zero
         *
         * @since 10
         */
        public int patch() {
            return (version.size()>3 ? version.get(3) : 0);
        }
        
        /**
         * Returns the optional <a href="#pre">pre-release</a> information.
         *
         * @return The optional pre-release information as a String
         */
        // 返回预发行信息
        public Optional<String> pre() {
            return pre;
        }
        
        /**
         * Returns the <a href="#build">build number</a>.
         *
         * @return The optional build number.
         */
        // 返回构建信息
        public Optional<Integer> build() {
            return build;
        }
        
        /**
         * Returns <a href="#opt">optional</a> additional identifying build
         * information.
         *
         * @return Additional build information as a String
         */
        // 返回附加信息
        public Optional<String> optional() {
            return optional;
        }
        
        /**
         * Compares this version to another.
         *
         * <p> Each of the components in the <a href="#verStr">version</a> is
         * compared in the following order of precedence: version numbers,
         * pre-release identifiers, build numbers, optional build information.
         * </p>
         *
         * <p> Comparison begins by examining the sequence of version numbers.
         * If one sequence is shorter than another, then the missing elements
         * of the shorter sequence are considered to be less than the
         * corresponding elements of the longer sequence. </p>
         *
         * <p> A version with a pre-release identifier is always considered to
         * be less than a version without one.  Pre-release identifiers are
         * compared numerically when they consist only of digits, and
         * lexicographically otherwise.  Numeric identifiers are considered to
         * be less than non-numeric identifiers.  </p>
         *
         * <p> A version without a build number is always less than one with a
         * build number; otherwise build numbers are compared numerically. </p>
         *
         * <p> The optional build information is compared lexicographically.
         * During this comparison, a version with optional build information is
         * considered to be greater than a version without one. </p>
         *
         * @param obj The object to be compared
         *
         * @return A negative integer, zero, or a positive integer if this
         * {@code Version} is less than, equal to, or greater than the
         * given {@code Version}
         *
         * @throws NullPointerException If the given object is {@code null}
         */
        @Override
        public int compareTo(Version obj) {
            return compare(obj, false);
        }
        
        /**
         * Compares this version to another disregarding optional build
         * information.
         *
         * <p> Two versions are compared by examining the version string as
         * described in {@link #compareTo(Version)} with the exception that the
         * optional build information is always ignored. </p>
         *
         * <p> This method provides ordering which is consistent with
         * {@code equalsIgnoreOptional()}. </p>
         *
         * @param obj The object to be compared
         *
         * @return A negative integer, zero, or a positive integer if this
         * {@code Version} is less than, equal to, or greater than the
         * given {@code Version}
         *
         * @throws NullPointerException If the given object is {@code null}
         */
        public int compareToIgnoreOptional(Version obj) {
            return compare(obj, true);
        }
        
        /**
         * Returns a string representation of this version.
         *
         * @return The version string
         */
        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder(version.stream().map(Object::toString).collect(Collectors.joining(".")));
    
            pre.ifPresent(v -> sb.append("-").append(v));
    
            if(build.isPresent()) {
                sb.append("+").append(build.get());
                if(optional.isPresent()) {
                    sb.append("-").append(optional.get());
                }
            } else {
                if(optional.isPresent()) {
                    sb.append(pre.isPresent() ? "-" : "+-");
                    sb.append(optional.get());
                }
            }
    
            return sb.toString();
        }
        
        /**
         * Determines whether this {@code Version} is equal to another object.
         *
         * <p> Two {@code Version}s are equal if and only if they represent the
         * same version string.
         *
         * @param obj The object to which this {@code Version} is to be compared
         *
         * @return {@code true} if, and only if, the given object is a {@code
         * Version} that is identical to this {@code Version}
         */
        @Override
        public boolean equals(Object obj) {
            boolean ret = equalsIgnoreOptional(obj);
            if(!ret) {
                return false;
            }
    
            Version that = (Version) obj;
            return (this.optional().equals(that.optional()));
        }
        
        /**
         * Determines whether this {@code Version} is equal to another
         * disregarding optional build information.
         *
         * <p> Two {@code Version}s are equal if and only if they represent the
         * same version string disregarding the optional build information.
         *
         * @param obj The object to which this {@code Version} is to be compared
         *
         * @return {@code true} if, and only if, the given object is a {@code
         * Version} that is identical to this {@code Version}
         * ignoring the optional build information
         */
        public boolean equalsIgnoreOptional(Object obj) {
            if(this == obj) {
                return true;
            }
    
            if(!(obj instanceof Version)) {
                return false;
            }
    
            Version that = (Version) obj;
    
            return (this.version().equals(that.version()) && this.pre().equals(that.pre()) && this.build().equals(that.build()));
        }
        
        /**
         * Returns the hash code of this version.
         *
         * @return The hashcode of this version
         */
        @Override
        public int hashCode() {
            int h = 1;
            int p = 17;
    
            h = p * h + version.hashCode();
            h = p * h + pre.hashCode();
            h = p * h + build.hashCode();
            h = p * h + optional.hashCode();
    
            return h;
        }
        
        private static boolean isSimpleNumber(String s) {
            for(int i = 0; i<s.length(); i++) {
                char c = s.charAt(i);
                char lowerBound = (i>0) ? '0' : '1';
                if(c<lowerBound || c>'9') {
                    return false;
                }
            }
            return true;
        }
        
        private int compare(Version obj, boolean ignoreOpt) {
            if(obj == null) {
                throw new NullPointerException();
            }
            
            int ret = compareVersion(obj);
            if(ret != 0) {
                return ret;
            }
            
            ret = comparePre(obj);
            if(ret != 0) {
                return ret;
            }
            
            ret = compareBuild(obj);
            if(ret != 0) {
                return ret;
            }
            
            if(!ignoreOpt) {
                return compareOptional(obj);
            }
            
            return 0;
        }
        
        private int compareVersion(Version obj) {
            int size = version.size();
            int oSize = obj.version().size();
            int min = Math.min(size, oSize);
            for(int i = 0; i<min; i++) {
                int val = version.get(i);
                int oVal = obj.version().get(i);
                if(val != oVal) {
                    return val - oVal;
                }
            }
            return size - oSize;
        }
        
        private int comparePre(Version obj) {
            Optional<String> oPre = obj.pre();
            if(!pre.isPresent()) {
                if(oPre.isPresent()) {
                    return 1;
                }
            } else {
                if(!oPre.isPresent()) {
                    return -1;
                }
                String val = pre.get();
                String oVal = oPre.get();
                if(val.matches("\\d+")) {
                    return (oVal.matches("\\d+") ? (new BigInteger(val)).compareTo(new BigInteger(oVal)) : -1);
                } else {
                    return (oVal.matches("\\d+") ? 1 : val.compareTo(oVal));
                }
            }
            return 0;
        }
        
        private int compareBuild(Version obj) {
            Optional<Integer> oBuild = obj.build();
            if(oBuild.isPresent()) {
                return (build.isPresent() ? build.get().compareTo(oBuild.get()) : -1);
            } else if(build.isPresent()) {
                return 1;
            }
            return 0;
        }
        
        private int compareOptional(Version obj) {
            Optional<String> oOpt = obj.optional();
            if(!optional.isPresent()) {
                if(oOpt.isPresent()) {
                    return -1;
                }
            } else {
                if(!oOpt.isPresent()) {
                    return 1;
                }
                return optional.get().compareTo(oOpt.get());
            }
            return 0;
        }
        
    }
    
}