import javax.swing.text.PlainDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;

public class JTextFieldCharLimit extends PlainDocument{
	private int limit; 

	public JTextFieldCharLimit(int limit){
		this.limit = limit;
	}
	public void insertString(int offset, String str, AttributeSet set) throws BadLocationException{
		if (str == null){
			return;
		} else if ((getLength() + str.length() - getLength()) <= limit){
			super.insertString(offset, str, set);
		}
	}
}