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Thread: need help with consuming key events.

  1. #1
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    Default 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();
    		}
    	}


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: need help with consuming key events.

    Can you make a small, complete program that compiles, executes and shows the problem?
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: need help with consuming key events.

    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();
    		}
     
    	}
     
    }

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: need help with consuming key events.

    The KeyEvent values are int, not char. Look at their values and see if (int)'n' is one of them.
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: need help with consuming key events.

    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?

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: need help with consuming key events.

    None are 'n'.
    No, there is one that has the value 'n'.
    Did you look at the values of the static KeyEvent variables that the code uses? Which one of them had the value: (int)'n'?
    If you don't understand my answer, don't ignore it, ask a question.

  7. The Following User Says Thank You to Norm For This Useful Post:

    antihero.mc (June 27th, 2014)

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    Default Re: need help with consuming key events.

    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 );
            }
     
        }
     
    }

  9. The Following 2 Users Say Thank You to GregBrannon For This Useful Post:

    antihero.mc (June 27th, 2014), Norm (June 27th, 2014)

  10. #8
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    Default Re: need help with consuming key events.

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

    --- Update ---

    AHHHH ok thank you both.

  11. #9
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    Default Re: need help with consuming key events.

    I don't know where you're finding that.
    Can you give some more details on where you are having problems? What is the "that" you refer to?
    If you don't understand my answer, don't ignore it, ask a question.

  12. #10
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    Default Re: need help with consuming key events.

    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.

  13. #11
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    Default Re: need help with consuming key events.

    So it looks like the simplest solution is to just check if the value is equal to "n" (110) and consume it. Thanks again to Norm and Greg.

    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();
     
    //	variable to store accepted inputs
    	StringBuilder inputString;
     
    	public TestClass(){
     
    //		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();
     
    	}
     
    	public void keyPressed(KeyEvent arg0) {
    		// TODO Auto-generated method stub
     
    	}
     
    	public void keyReleased(KeyEvent arg0) {
    		// TODO Auto-generated method stub
     
    	}
     
    	public void keyTyped(KeyEvent k) {
     
    //		notify that a key has been captured
    		System.out.println("In KeyTyped() method.");
     
    		int input = k.getKeyChar();
     
    //		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_PERIOD) ||
                    (inputField.getText().contains(".") && input==KeyEvent.VK_PERIOD) ||
                    input==110
    				){
    			k.consume();
    		}
     
    //		record and display keys
    		else{
    			inputString.append( "" + (char)input );
    	        System.out.println( "Recorded input is now: " + inputString );
    		}
     
    	}
     
    }
    Last edited by antihero.mc; June 28th, 2014 at 01:31 AM.

  14. #12
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    Default Re: need help with consuming key events.

    Try adding a println() statement that prints out the value of input. Then execute the code and press all the keys one at a time to see what is passed to the variable: input. I don't think VK_DECIMAL is ever passed.

    NOTE: Hardcoding 110 in a program without any comments is not a good technique. Better to use 'n'.

    I don't think that code using VK_DECIMAL is needed.
    If you don't understand my answer, don't ignore it, ask a question.

  15. The Following User Says Thank You to Norm For This Useful Post:

    GregBrannon (June 28th, 2014)

  16. #13
    Super Moderator Norm's Avatar
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    Default Re: need help with consuming key events.

    The formatting of the if statement is hard to understand. Also some comments would make it easier to understand. Here's a rewrite:
                       //  don't consume: digit, backspace, delete or period
    		if (!(Character.isDigit(input) ||
    				(input==KeyEvent.VK_BACK_SPACE) ||
    				(input==KeyEvent.VK_DELETE) ||
    				(input==KeyEvent.VK_PERIOD) ) 
                         // consume . if already have one
                         || (inputField.getText().contains(".")
    			  &&  input==KeyEvent.VK_PERIOD) ) {
    			k.consume();
    		}
    If you don't understand my answer, don't ignore it, ask a question.

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