An extension of PlainDocument that restricts the length of its content

   


import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.PlainDocument;

public class MaxLengthDocument extends PlainDocument {
  private int max;

  public MaxLengthDocument(int maxLength) {
    max = maxLength;
  }

  public void insertString(int offset, String str, AttributeSet a) throws BadLocationException {
    if (getLength() + str.length() > max)
      java.awt.Toolkit.getDefaultToolkit().beep();
    else
      super.insertString(offset, str, a);
  }

}

class MainClass{
  public static void main(String[] a){
      Document doc = new MaxLengthDocument(5); // set maximum length to 5
      JTextField field = new JTextField(doc, "", 8);

      JPanel flowPanel = new JPanel();
      flowPanel.add(field);
      JFrame frame = new JFrame("MaxLengthDocument demo");
      frame.setContentPane(flowPanel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setSize(160, 80);
      frame.setVisible(true);
  }
}

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An extension of PlainDocument that restricts the length of its content : Document Event « Swing JFC « Java

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