Java Swing How to - Make sure that a user doesn't enter numbers in a string in JTextField

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Question

We would like to know how to make sure that a user doesn't enter numbers in a string in JTextField.

Answer

import java.awt.BorderLayout;
/*from   w w w . j a v a2  s .co  m*/
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;

class NonNumericDocument extends PlainDocument {
  @Override
  public void insertString(int offs, String str, AttributeSet a)
      throws BadLocationException {
    if (str == null) {
      return;
    }
    char[] arr = str.toCharArray();
    for (int i = 0; i < arr.length; i++) {
      if (Character.isDigit(arr[i]) || !Character.isLetter(arr[i])) {
        return;
      }
    }
    super.insertString(offs, new String(str), a);
  }
}

public class Main extends JFrame {
  JTextField tf;

  public void prepareAndShowGUI() {
    tf = new JTextField(30);
    tf.setDocument(new NonNumericDocument());
    getContentPane().add(tf, BorderLayout.NORTH);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    setVisible(true);
  }

  public static void main(String[] args) {
    Main tFrame = new Main();
    tFrame.prepareAndShowGUI();
  }
}

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