Java键盘事件监听(2)修改：使用监听键盘事件，而不是改写JTextField

package com.han;

import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;

/**
 * 键盘事件监听(2)修改：使用监听键盘事件，而不是改写JTextField
 * @author HAN
 *
 */
public class KeyEvent_2_Modified extends JFrame {

	/**
	 * 
	 */
	private static final long serialVersionUID = -3184139070064852786L;

	public KeyEvent_2_Modified() {
		// TODO Auto-generated constructor stub
		final Container container = getContentPane();
		container.setLayout(new FlowLayout());
		JLabel label = new JLabel("实现只允许输入数字的文本框：");
		final JTextField textField = new JTextField(10);
		container.add(label);
		container.add(textField);
		
		textField.addKeyListener(new KeyAdapter() {
			
			@Override
			public void keyPressed(KeyEvent e) { // keyPressed 与 keyReleased是有时间差的！！
				// TODO Auto-generated method stub
				if (e.getKeyCode() == KeyEvent.VK_ENTER) {
					char[] text = textField.getText().toCharArray();
					for (char ch : text) {
						if (!Character.isDigit(ch)) {
//							textField.removeKeyListener(this);
							JOptionPane.showMessageDialog(container, 
									"Your input contains non-digit characters !", 
									"Warning", JOptionPane.WARNING_MESSAGE);
							textField.setText("");
//							textField.addKeyListener(this);
							return;
						}
					}
				}
			}
		});
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		KeyEvent_2_Modified frame = new KeyEvent_2_Modified();
		frame.setTitle("实现只允许输入数字的文本框(2)");
		frame.pack();
		frame.setVisible(true);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}

}