Java设计模式--缺省适配器模式

我认为这个模式比较常见，还记得我们学习Swing的时候吗，有没有见过很多Adapter？那时候不知道Adapter的意义所在，但至少知道他能够省去我们不需要的实现。

这个社会有N中职业（job），但是每个人（people）只可能从事其中一种或者几种，职业类型设成一个接口，难道每次给人设置职业的时候要全部实现吗？在这里就要有一个缺省适配器，缺省适配器是个抽象类，仅仅implements而不实现。然后客户端直接使用Adapter即可选择需要实现的方法，而不用实现全部。

Job

package com.design.adapter.defaultadapter;

public interface Job {

    void police();

    void programmer();

    void teacher();

    void productManager();

}

DefaultJobAdapter

package com.design.adapter.defaultadapter;

public abstract class DefaultJobAdapter implements Job {

    @Override
    public void police() {

    }

    @Override
    public void programmer() {

    }

    @Override
    public void teacher() {

    }

    @Override
    public void productManager() {

    }
}

客户端

package com.design.adapter.defaultadapter;

public class Client {

    public static void main(String[] args){
        People people = new People();

        people.addJob(new DefaultJobAdapter() {
            @Override
            public void programmer() {
                System.out.println("写代码，与产品撕逼");
            }
        });
    }

}

class People{

    public void addJob(Job job){

    }
}

这样，就不需要写不需要的代码啦。

看一下WindowAdapter

客户端调用情况

package com.design.adapter.defaultadapter;

import javax.swing.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class TestWindowsAdapter {

    public static void main(String[] args){
        JFrame frame = new JFrame("Hello");
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowOpened(WindowEvent e) {
                super.windowOpened(e);
            }

            @Override
            public void windowClosed(WindowEvent e) {
                super.windowClosed(e);
            }

            @Override
            public void windowLostFocus(WindowEvent e) {
                super.windowLostFocus(e);
            }
        });

    }
}

addWindowListener的实现

    /**
     * Adds the specified window listener to receive window events from
     * this window.
     * If l is null, no exception is thrown and no action is performed.
     * <p>Refer to <a href="doc-files/AWTThreadIssues.html#ListenersThreads"
     * >AWT Threading Issues</a> for details on AWT's threading model.
     *
     * @param   l the window listener
     * @see #removeWindowListener
     * @see #getWindowListeners
     */
    public synchronized void addWindowListener(WindowListener l) {
        if (l == null) {
            return;
        }
        newEventsOnly = true;
        windowListener = AWTEventMulticaster.add(windowListener, l);
    }

WindowAdapter的实现

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt.event;

/**
 * An abstract adapter class for receiving window events.
 * The methods in this class are empty. This class exists as
 * convenience for creating listener objects.
 * <P>
 * Extend this class to create a <code>WindowEvent</code> listener
 * and override the methods for the events of interest. (If you implement the
 * <code>WindowListener</code> interface, you have to define all of
 * the methods in it. This abstract class defines null methods for them
 * all, so you can only have to define methods for events you care about.)
 * <P>
 * Create a listener object using the extended class and then register it with
 * a Window using the window's <code>addWindowListener</code>
 * method. When the window's status changes by virtue of being opened,
 * closed, activated or deactivated, iconified or deiconified,
 * the relevant method in the listener
 * object is invoked, and the <code>WindowEvent</code> is passed to it.
 *
 * @see WindowEvent
 * @see WindowListener
 * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/windowlistener.html">Tutorial: Writing a Window Listener</a>
 *
 * @author Carl Quinn
 * @author Amy Fowler
 * @author David Mendenhall
 * @since 1.1
 */
public abstract class WindowAdapter
    implements WindowListener, WindowStateListener, WindowFocusListener
{
    /**
     * Invoked when a window has been opened.
     */
    public void windowOpened(WindowEvent e) {}

    /**
     * Invoked when a window is in the process of being closed.
     * The close operation can be overridden at this point.
     */
    public void windowClosing(WindowEvent e) {}

    /**
     * Invoked when a window has been closed.
     */
    public void windowClosed(WindowEvent e) {}

    /**
     * Invoked when a window is iconified.
     */
    public void windowIconified(WindowEvent e) {}

    /**
     * Invoked when a window is de-iconified.
     */
    public void windowDeiconified(WindowEvent e) {}

    /**
     * Invoked when a window is activated.
     */
    public void windowActivated(WindowEvent e) {}

    /**
     * Invoked when a window is de-activated.
     */
    public void windowDeactivated(WindowEvent e) {}

    /**
     * Invoked when a window state is changed.
     * @since 1.4
     */
    public void windowStateChanged(WindowEvent e) {}

    /**
     * Invoked when the Window is set to be the focused Window, which means
     * that the Window, or one of its subcomponents, will receive keyboard
     * events.
     *
     * @since 1.4
     */
    public void windowGainedFocus(WindowEvent e) {}

    /**
     * Invoked when the Window is no longer the focused Window, which means
     * that keyboard events will no longer be delivered to the Window or any of
     * its subcomponents.
     *
     * @since 1.4
     */
    public void windowLostFocus(WindowEvent e) {}
}

看一下WindowListener

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt.event;

import java.util.EventListener;

/**
 * The listener interface for receiving window events.
 * The class that is interested in processing a window event
 * either implements this interface (and all the methods it
 * contains) or extends the abstract <code>WindowAdapter</code> class
 * (overriding only the methods of interest).
 * The listener object created from that class is then registered with a
 * Window using the window's <code>addWindowListener</code>
 * method. When the window's status changes by virtue of being opened,
 * closed, activated or deactivated, iconified or deiconified,
 * the relevant method in the listener object is invoked, and the
 * <code>WindowEvent</code> is passed to it.
 *
 * @author Carl Quinn
 *
 * @see WindowAdapter
 * @see WindowEvent
 * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/windowlistener.html">Tutorial: How to Write Window Listeners</a>
 *
 * @since 1.1
 */
public interface WindowListener extends EventListener {
    /**
     * Invoked the first time a window is made visible.
     */
    public void windowOpened(WindowEvent e);

    /**
     * Invoked when the user attempts to close the window
     * from the window's system menu.
     */
    public void windowClosing(WindowEvent e);

    /**
     * Invoked when a window has been closed as the result
     * of calling dispose on the window.
     */
    public void windowClosed(WindowEvent e);

    /**
     * Invoked when a window is changed from a normal to a
     * minimized state. For many platforms, a minimized window
     * is displayed as the icon specified in the window's
     * iconImage property.
     * @see java.awt.Frame#setIconImage
     */
    public void windowIconified(WindowEvent e);

    /**
     * Invoked when a window is changed from a minimized
     * to a normal state.
     */
    public void windowDeiconified(WindowEvent e);

    /**
     * Invoked when the Window is set to be the active Window. Only a Frame or
     * a Dialog can be the active Window. The native windowing system may
     * denote the active Window or its children with special decorations, such
     * as a highlighted title bar. The active Window is always either the
     * focused Window, or the first Frame or Dialog that is an owner of the
     * focused Window.
     */
    public void windowActivated(WindowEvent e);

    /**
     * Invoked when a Window is no longer the active Window. Only a Frame or a
     * Dialog can be the active Window. The native windowing system may denote
     * the active Window or its children with special decorations, such as a
     * highlighted title bar. The active Window is always either the focused
     * Window, or the first Frame or Dialog that is an owner of the focused
     * Window.
     */
    public void windowDeactivated(WindowEvent e);
}