Java只允许输入数字的文本框

Java只允许输入数字的文本框：

package com.han;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.PlainDocument;
/**
* Customized fields can easily be created by extending the model
* and changing the default model provided. For example,
* the following piece of code will create a field that holds only
* digit characters. It will work even if text is pasted into from
* the clipboard or it is altered via programmatic changes.
* @author HAN
*
*/
public class DigitOnlyField extends JTextField {
/**
*
*/
private static final long serialVersionUID = 8384787369612949227L;
public DigitOnlyField（int cols） {
// super（）可以被自动调用，但是有参构造方法并不能被自动调用，只能依赖
// super关键字显示地调用父类的构造方法
super（cols）;
}
protected Document createDefaultModel（） {
return new UpperCaseDocument（）;
}
static class UpperCaseDocument extends PlainDocument {
/**
*
*/
private static final long serialVersionUID = -4170536906715361215L;
public void insertString（int offs, String str, AttributeSet a）
throws BadLocationException {
if （str == null） {
return;
}
char[] upper = str.toCharArray（）;
String filtered = "";
for （int i = 0; i < upper.length; i++） {
if （Character.isDigit（Character.codePointAt（upper, i）））{
filtered += upper[i];
}
}
super.insertString（offs, filtered, a）;
}
}
}