Java 界面-焦点事件类

[ 相关信息]
焦点事件类(FocusEvent)是指用户程序界面的组件失去焦点(即焦点从一个对象转移到另外一个对象)时，就会发生焦点事件。
使用焦点事件必须给组件增加一个 FocusListener 接口的事件处理器,该接口包含以下两个方法：
1）void focusGained(FocusEvent e)：当获得焦点时发生。
2）void focusLost(FocusEvent e)：当失去焦点时发生。

[具体程序实现]

package sup.orange.learn;

import java.awt.*;
import java.awt.event.*;

/**
 * Created by re-x on 10/28/14.
 */
public class FocusEventDemo extends Frame{
    TextArea textarea;
    TextField textfield;

    public FocusEventDemo () {
        super();
        init();
    }

    public static void main(String[] args) {
        new FocusEventDemo();
    }

    public void init() {
        setLayout(new GridLayout(2, 1));
        textarea = new TextArea();
        textarea.addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                textarea.setText("gained");
            }

            @Override
            public void focusLost(FocusEvent e) {
                textarea.setText("lost");
            }
        });

        textfield = new TextField();
        textfield.addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                textfield.setText("textfield gained");
            }

            @Override
            public void focusLost(FocusEvent e) {
                textfield.setText("textfield lost");
            }
        });

        add(textarea);
        add(textfield);
        addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                super.windowClosing(e);
                dispose();
                System.exit(0);
            }
        });
        setSize(200, 500);
        setVisible(true);
    }
}