http://www.rgagnon.com/javadetails/java-0198.html
import javax.swing.text.PlainDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
public class JTextFieldLimit extends PlainDocument {
private int limit;
JTextFieldLimit(int limit) {
super();
this.limit = limit;
}
public void insertString( int offset, String str, AttributeSet attr ) throws BadLocationException {
if (str == null) return;
if ((getLength() + str.length()) <= limit) {
super.insertString(offset, str, attr);
}
}
}
然后
import java.awt.*;
import javax.swing.*;
public class DemoJTextFieldWithLimit extends JApplet{
JTextField textfield1;
JLabel label1;
public void init() {
getContentPane().setLayout(new FlowLayout());
//
label1 = new JLabel("max 10 chars");
textfield1 = new JTextField(15);
getContentPane().add(label1);
getContentPane().add(textfield1);
textfield1.setDocument
(new JTextFieldLimit(10));
}
}
（谷歌的第一个结果）
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