超简单实现一个只接收数字的类[JAVA]

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JTextField;
//
public class NumberField extends JTextField implements KeyListener
{
private static final long serialVersionUID = 1L;
NumberField(int columns)
{
setColumns(columns);
addKeyListener(this);	//必需的
}
public void keyPressed(KeyEvent e){
}
public void keyReleased(KeyEvent e){
}
public void keyTyped(KeyEvent e)
{
char key = e.getKeyChar();

//只接收输入数字、'.'和'-'
if ((key >= KeyEvent.VK_0 		&&
key <= KeyEvent.VK_9)		||
key == KeyEvent.VK_PERIOD 	||
key == KeyEvent.VK_MINUS
)
{
if (key == KeyEvent.VK_PERIOD)
{
//如果已经存在'.'，则不处理
String str = getText();
if (str.indexOf('.') != -1)
e.consume();
}
//输入负号
else if (key == KeyEvent.VK_MINUS)
{
if (getText().length() != 0)
e.consume();
}
}
else	//拒绝其它字符输入
{
e.consume();
}
}
}