JTextField设置最大长度的小代码

textfield.setDocument(new PlainDocument() {
int MAX_LENGTH = 20;
public void insertString(int offset, String s,
AttributeSet attributeSet) throws BadLocationException {
if (s == null || offset < 0) {
return;
}
for (int i = 0; i < s.length(); i++) {
if (getLength() > MAX_LENGTH - 1) {
break;
}
super.insertString(offset + i, s.substring(i, i + 1),
attributeSet);
}
return;
}
});