java.awt.event.ActionEvent.CTRL_MASK what is it?

[Gourav Das]

Can someone please tell me what the CTRL_MASK does , i read from the docs that its a control modifier .. and when i try to print it out using  System.out.println(ActionEvent.CTRL_MASK) while holding ctrl key , it results in 2 , and when not pressing control key , its still 2.

I have written a program ,,, here's the code , line 93 shows it

package stopwatch_package;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

@SuppressWarnings("serial")
public class StopwatchApplication extends JFrame {

	JButton startButton = new JButton();
	JButton stopButton = new  JButton();
	JButton exitButton = new JButton();
	JLabel startLabel = new JLabel();
	JLabel stopLabel = new JLabel();
	JLabel elapsedLabel = new JLabel();
	JTextField startTextField = new JTextField();
	JTextField stopTextField = new JTextField();
	JTextField elapsedTextField = new JTextField();
	long startTime;
	long stopTime;
	
	//@SuppressWarnings("deprecation")
	public static void main(String[] args) {
		StopwatchApplication object = new StopwatchApplication();
		
		object.setVisible(true);
	}
	
	StopwatchApplication()
	{
		setTitle("Simple Stopwatch");
		setSize(400,200);
		getContentPane().setLayout(new GridBagLayout());
		GridBagConstraints gridBagConstraints = new GridBagConstraints();
		
		
		addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				System.exit(0);
			}
		});
		
		
		startButton.setText("Start");
		gridBagConstraints.gridx=0;
		gridBagConstraints.gridy=0;
		getContentPane().add(startButton,gridBagConstraints);
		startButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				startButtonActionPerformed(e);
			}
		});
		
		
		startLabel.setText("Start Time");
		gridBagConstraints.gridx=1;
		gridBagConstraints.gridy=0;
		getContentPane().add(startLabel,gridBagConstraints);
		
		startTextField.setText("");
		startTextField.setColumns(15);
		gridBagConstraints.gridx=2;
		gridBagConstraints.gridy=0;
		getContentPane().add(startTextField,gridBagConstraints);
		
		stopButton.setText("Stop");
		gridBagConstraints.gridx=0;
		gridBagConstraints.gridy=1;
		getContentPane().add(stopButton,gridBagConstraints);
		stopButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				stopButtonActionPerformed(e);
			}
		});
		
		stopLabel.setText("Stop Time");
		gridBagConstraints.gridx=1;
		gridBagConstraints.gridy=1;
		getContentPane().add(stopLabel,gridBagConstraints);
		
		stopTextField.setText("");
		stopTextField.setColumns(15);
		gridBagConstraints.gridx=2;
		gridBagConstraints.gridy=1;
		getContentPane().add(stopTextField,gridBagConstraints);
		
		exitButton.setText("Exit");
		gridBagConstraints.gridx=0;
		gridBagConstraints.gridy=2;
		getContentPane().add(exitButton,gridBagConstraints);
		exitButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				System.out.println(String.valueOf(ActionEvent.CTRL_MASK));
				exitButtonActionPerformed(e);
			}
		});
		
		elapsedLabel.setText("Elapsed Time");
		gridBagConstraints.gridx=1;
		gridBagConstraints.gridy=2;
		getContentPane().add(elapsedLabel,gridBagConstraints);
		
		elapsedTextField.setText("");
		elapsedTextField.setColumns(15);
		gridBagConstraints.gridx=2;
		gridBagConstraints.gridy=2;
		getContentPane().add(elapsedTextField,gridBagConstraints);
		
	
		pack();
		
	}
	
	public void startButtonActionPerformed(ActionEvent e) {
		startTime = System.currentTimeMillis();
		startTextField.setText(String.valueOf(startTime));
		stopTextField.setText("");
		elapsedTextField.setText("");
	}
	
	public void stopButtonActionPerformed(ActionEvent e) {
		stopTime=System.currentTimeMillis();
		stopTextField.setText(String.valueOf(stopTime));
		elapsedTextField.setText(String.valueOf(((double)(stopTime-startTime)/1000)));
	}
	
	public void exitButtonActionPerformed(ActionEvent e) {
		startTextField.setText("");
		stopTextField.setText("");
		elapsedTextField.setText("");
	}
	
}

[Paul Clapham]

And what key did you press (apart from the Ctrl key) to cause that ActionEvent?

[Gourav Das]

Paul Clapham wrote:And what key did you press (apart from the Ctrl key) to cause that ActionEvent?

every other key , 'x','y','a', etc.. , still every time the result is 2 which is printed out in the console.... the key is pressed when i click on the "Button Exit"... :(

[Paul Clapham]

So just to confirm -- you are pressing the Ctrl key and some alphabetic key and clicking with the mouse on the button? Did you try finding out what alphabetic key was pressed at the same time?

I've never tried that and I wouldn't have expected to get key-press information when you click on a button. Apparently what I expected was correct.

I would expect that if you wrote a KeyListener then you would get the information you're looking for. But in real life, users don't expect clicking on a button in a GUI to be affected by what keys you happen to be pressing at the time.

[Gourav Das]

Paul Clapham wrote:So just to confirm -- you are pressing the Ctrl key and some alphabetic key and clicking with the mouse on the button? Did you try finding out what alphabetic key was pressed at the same time?

I've never tried that and I wouldn't have expected to get key-press information when you click on a button. Apparently what I expected was correct.

I would expect that if you wrote a KeyListener then you would get the information you're looking for. But in real life, users don't expect clicking on a button in a GUI to be affected by what keys you happen to be pressing at the time.

Actually  , i just was playing around with the CTRL_MASK , after reading the docs ... Can you please tell me what it is used for?

Herer are the several fields in ActionEvent Class..

[Rob Camick]

System.out.println(ActionEvent.CTRL_MASK);

while holding ctrl key , it results in 2 , and when not pressing control key , its still 2.

Yes, because you are just printing a static value from the ActionEvent class.

You need to invoke the getModifiers() method of the ActionEvent to see if any modifier key was used when the button was clicked.

Here is a basic ActionListener that displays the modifier keys that were pressed when the button was clicked:

ActionListener listener = new ActionListener()
{
	public void actionPerformed(ActionEvent e)
	{
		System.out.println("Command: " + e.getActionCommand());
		int modifiers = e.getModifiers();
		System.out.println("\tALT : " + checkMask(modifiers, ActionEvent.ALT_MASK));
		System.out.println("\tCTRL : " + checkMask(modifiers, ActionEvent.CTRL_MASK));
		System.out.println("\tMETA : " + checkMask(modifiers, ActionEvent.META_MASK));
		System.out.println("\tSHIFT: " + checkMask(modifiers, ActionEvent.SHIFT_MASK));
	}

	private boolean checkMask(int modifiers, int mask)
	{
		return ((modifiers & mask) == mask);
	}
};

[Gourav Das]

Rob Camick wrote:. . .

Thank You

[Paul Clapham]

Rob Camick wrote:You need to invoke the getModifiers() method of the ActionEvent to see if any modifier key was used when the button was clicked.

Well, that part I should have known. But I'll be damned, it actually works with button clicks.

[Junilu Lacar]

The term "mask" refers to a bit mask, which is why Rob wrote (modifiers & mask) == mask -- that is, take the modifiers value and mask it (perform bitwise & operation) with the bits in the mask variable to see if the bits that are set in mask are all set in modifiers

If modifiers == 7, that's 0111 in binary. A mask of 2 is 0010 in binary.

  0111     modifiers
& 0010     mask
------
  0010  == mask

If you look at the values of the mask constants, you'll see that each mask constant represents a bit position that is set. That is, mask values are 1, 2, 4, 8 (binary 0001, 0010, 0100, 1000, respectively). If you wanted to check if both the CTRL and SHIFT keys were pressed, you'd write checkMask(modifiers, CTRL_MASK + SHIFT_MASK). In general, you can check for any combination of keys pressed by using the sum of their respective mask constants.

I'd probably rename that method to read like this instead: isKeyPressed(modifiers, CTRL_MASK + SHIFT_MASK) for better semantics.