Watchable.java

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package java.nio.file;

import java.io.IOException;

/**
 * An object that may be registered with a watch service so that it can be
 * <em>watched</em> for changes and events.
 *
 * <p> This interface defines the {@link #register register} method to register
 * the object with a {@link WatchService} returning a {@link WatchKey} to
 * represent the registration. An object may be registered with more than one
 * watch service. Registration with a watch service is cancelled by invoking the
 * key's {@link WatchKey#cancel cancel} method.
 *
 * @see Path#register
 * @since 1.7
 */
// 指示可被监视的对象，如Path
public interface Watchable {
    
    /**
     * Registers an object with a watch service.
     *
     * <p> If the file system object identified by this object is currently
     * registered with the watch service then the watch key, representing that
     * registration, is returned after changing the event set or modifiers to
     * those specified by the {@code events} and {@code modifiers} parameters.
     * Changing the event set does not cause pending events for the object to be
     * discarded. Objects are automatically registered for the {@link
     * StandardWatchEventKinds#OVERFLOW OVERFLOW} event. This event is not
     * required to be present in the array of events.
     *
     * <p> Otherwise the file system object has not yet been registered with the
     * given watch service, so it is registered and the resulting new key is
     * returned.
     *
     * <p> Implementations of this interface should specify the events they
     * support.
     *
     * @param watcher   the watch service to which this object is to be registered
     * @param events    the events for which this object should be registered
     * @param modifiers the modifiers, if any, that modify how the object is registered
     *
     * @return a key representing the registration of this object with the
     * given watch service
     *
     * @throws UnsupportedOperationException if unsupported events or modifiers are specified
     * @throws IllegalArgumentException      if an invalid of combination of events are modifiers are specified
     * @throws ClosedWatchServiceException   if the watch service is closed
     * @throws IOException                   if an I/O error occurs
     * @throws SecurityException             if a security manager is installed and it denies an unspecified
     *                                       permission required to monitor this object. Implementations of
     *                                       this interface should specify the permission checks.
     */
    /*
     * 为当前路径指示的目录(树)注册监听服务watcher。
     *
     * watcher  : 目录监视服务，其获取途径为：FileSystems -> FileSystem -> WatchService
     * events   : 监视的事件类型；通常从StandardWatchEventKinds中获取
     * modifiers: 对被监视事件的修饰，参见ExtendedWatchEventModifier(通常用这个，可以决定是否监视子目录)和SensitivityWatchEventModifier
     */
    WatchKey register(WatchService watcher, WatchEvent.Kind<?>[] events, WatchEvent.Modifier... modifiers) throws IOException;
    
    /**
     * Registers an object with a watch service.
     *
     * <p> An invocation of this method behaves in exactly the same way as the
     * invocation
     * <pre>
     *     watchable.{@link #register(WatchService, WatchEvent.Kind[], WatchEvent.Modifier[]) register}(watcher, events, new WatchEvent.Modifier[0]);
     * </pre>
     *
     * @param watcher the watch service to which this object is to be registered
     * @param events  the events for which this object should be registered
     *
     * @return a key representing the registration of this object with the
     * given watch service
     *
     * @throws UnsupportedOperationException if unsupported events are specified
     * @throws IllegalArgumentException      if an invalid of combination of events are specified
     * @throws ClosedWatchServiceException   if the watch service is closed
     * @throws IOException                   if an I/O error occurs
     * @throws SecurityException             if a security manager is installed and it denies an unspecified
     *                                       permission required to monitor this object. Implementations of
     *                                       this interface should specify the permission checks.
     */
    /*
     * 为当前路径指示的目录(树)注册监听服务watcher，不会监视子目录。
     *
     * watcher  : 目录监视服务，其获取途径为：FileSystems -> FileSystem -> WatchService
     * events   : 监视的事件类型；通常从StandardWatchEventKinds中获取
     */
    WatchKey register(WatchService watcher, WatchEvent.Kind<?>... events) throws IOException;
    
}