使用PlainDocument设置最大限制。这是一个粗略的草图：

Use PlainDocument to set the max limit. Here is a rough sketch :

public class JTextFieldLimit extends PlainDocument {

  public void insertString( int offset, String  str, AttributeSet attr ) throws BadLocationException {
//put yoyr max length validation logic

super.insertString(offset, str, attr);
  }
}