Thread: need help with consuming key events.

I am trying to create an event handler for two JTextFields to only allow numerical input. It consumes all letter but for some reason the "n" key still gets through. I have the spaghetti code below. Can anyone tell me what i'm not getting?

public void keyTyped(KeyEvent in) {
		char input = in.getKeyChar();
		if (in.getSource() == scaleField){
			if (!(Character.isDigit(input) ||
					(input==KeyEvent.VK_BACK_SPACE) ||
					(input==KeyEvent.VK_DELETE) ||
					(input==KeyEvent.VK_DECIMAL) ||
					(input==KeyEvent.VK_PERIOD)) ||
					(scaleField.getText().contains(".") &&
					(input==KeyEvent.VK_DECIMAL ||
					input==KeyEvent.VK_PERIOD))){
				in.consume();
			}
		}else if (!(Character.isDigit(input) ||
				(input==KeyEvent.VK_BACK_SPACE) ||
				(input==KeyEvent.VK_DELETE))){
			in.consume();
		}
	}

Thanks for the quick reply. Here it is:

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
 
 
public class Main extends JFrame implements KeyListener{
	private static final long serialVersionUID = 1L;
	JTextField inputField = new JTextField(20);
	JPanel contentPane = new JPanel();
 
	public Main(){
 
		inputField.addKeyListener(this);
		contentPane.add(inputField);
		add(contentPane);
		pack();
		setDefaultCloseOperation(EXIT_ON_CLOSE);
		setVisible(true);
 
	}
 
	public static void main(String[] args) {
 
		new Main();
 
	}
 
	@Override
	public void keyPressed(KeyEvent arg0) {
		// TODO Auto-generated method stub
 
	}
 
	@Override
	public void keyReleased(KeyEvent arg0) {
		// TODO Auto-generated method stub
 
	}
 
	@Override
	public void keyTyped(KeyEvent k) {
		char input = k.getKeyChar();
		if (!(Character.isDigit(input) ||
				(input==KeyEvent.VK_BACK_SPACE) ||
				(input==KeyEvent.VK_DELETE) ||
				(input==KeyEvent.VK_DECIMAL) ||
				(input==KeyEvent.VK_PERIOD)) ||
				(inputField.getText().contains(".") &&
				(input==KeyEvent.VK_DECIMAL ||
				input==KeyEvent.VK_PERIOD))){
			k.consume();
		}
 
	}
 
}

Hmmm. None are 'n'. All of the KeyEvents are actual integers. But it seems like somehow allowing decimals through is also allowing the "n" key through and even consuming the "n" key specifically before the main if statement doesn't catch it. Weird. Any recommendations?

I'm not sure you got Norm's point: The method getKeyChar() returns a char value, but the constants you're using for comparison are int values. The ASCII value of 'n' is 110 which, if you refer to this chart, you can see is the value for VK_DECIMAL.

Think about that a while and see if you can come up with a solution.

BTW - your runnable example is pretty good, but it's lacking in code to tell a person what's going on. I've improved it some so that you can see what's going on while the program is running. This is one of the techniques I recommend you use when debugging your code.

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
 
 
public class TestClass extends JFrame implements KeyListener{
    private static final long serialVersionUID = 1L;
    JTextField inputField = new JTextField(20);
    JPanel contentPane = new JPanel();
 
    // GB: a variable in which to store accepted inputs
    StringBuilder inputString;
 
    public TestClass()
    {
        // GB: initialize instance variables
        inputString = new StringBuilder();
 
        inputField.addKeyListener(this);
        contentPane.add(inputField);
        add(contentPane);
        pack();
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
 
    }
 
    public static void main(String[] args) {
 
        new TestClass();
 
    }
 
    @Override
    public void keyPressed(KeyEvent arg0) {
        // TODO Auto-generated method stub
 
    }
 
    @Override
    public void keyReleased(KeyEvent arg0) {
        // TODO Auto-generated method stub
 
    }
 
    @Override
    public void keyTyped(KeyEvent k)
    {
        // GB: to notify that a key has been captured
        System.out.println( "In keyTyped() method." );
 
        int input = k.getKeyChar();
 
        // GB: to display the value of the captured key
        System.out.println( "Input value is (int): " + input );
 
        if (!(Character.isDigit(input) ||
                (input==KeyEvent.VK_BACK_SPACE) ||
                (input==KeyEvent.VK_DELETE) ||
                (input==KeyEvent.VK_DECIMAL) ||
                (input==KeyEvent.VK_PERIOD)) ||
                (inputField.getText().contains(".") &&
                        (input==KeyEvent.VK_DECIMAL ||
                        input==KeyEvent.VK_PERIOD))){
            k.consume();
        }
        // GB: to record and display the keys that are recorded 
        else
        {
            inputString.append( "" + (char)input );
            System.out.println( "Recorded input is now: " + inputString );
        }
 
    }
 
}

Sorry. Still pretty green. I don't know where you're finding that.

--- Update ---

AHHHH ok thank you both.

I don't know where you're finding that.

Please be specific. I don't know what you're asking or if you're asking at all. I provided links to all but an ASCII table which you can find easily by searching. Or if you mean the details of the getKeyChar() method, refer to the KeyEvent API.