Logical expressions in java

Question

So on Java , an "AND" statement is &&, "OR" statement is ||...

What about for XOR then... that is if I have two choices. I HAVE to pick one, but I can't pick both.

HOWEVER,

private class CheckBoxListener implements ItemListener{
    public void itemStateChanged(ItemEvent e)
    {
    if(one.isSelected()^two.isSelected()){

    thehandler handler = new thehandler();
    button.addActionListener(handler);

        }   

 }}

Even if I have both checkboxes selected, the button is 'enabled'. This is the handler for the button fyi:

private class thehandler implements ActionListener{
        public void actionPerformed(ActionEvent event){

    dispose();
}

So if both are selected, and If i click the button. the frame should not dispose. It should only dispose when either one of them is selected.

ide · Accepted Answer · 2011-02-21T21:47:53.067

6

^ is the XOR operator in Java.

Regarding your Swing problem, the problem is that you are not inspecting the state of the checkboxes when the button is clicked, but rather when the checkboxes are selected. You should instead have something like this:

private class ButtonActionListener implements ActionListener {

    /*
     * You will probably define a constructor that accepts the two checkboxes
     * as arguments.
     */

    @Override
    public void actionPerformed(ActionEvent event) {
        if (one.isSelected() ^ two.isSelected()) {
            dispose();
        }
    }
}

The alternative approach is to create one instance of the ActionListener. You would add it with addActionListener when exactly one of the checkboxes is checked, and remove it with removeActionListener otherwise:

private class CheckBoxListener implements ItemListener {

    private ActionListener buttonActionListener = new thehandler();

    @Override
    public void itemStateChanged(ItemEvent event) {
        if(one.isSelected() ^ two.isSelected()) {
            button.addActionListener(buttonActionListener);
        } else {
            button.removeActionListener(buttonActionListener);
        }
    }
}

edited Feb 21 '11 at 21:47

answered Feb 21 '11 at 20:22

ide

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No, that's the **bitwise** XOR, not a logical one. – Matt Ball Feb 21 '11 at 20:22
6

It's both bitwise and logical. See [section 15.22](http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.22) of the Java language specification. – Ted Hopp Feb 21 '11 at 20:27
Neat, I never knew you could use `^` on booleans in Java. – Matti Virkkunen Feb 21 '11 at 20:28
Me too, I didn't know you could use it for both. Thanks! – Feb 21 '11 at 20:36
I have updated my question. The code is still not complying with the ^ or != – razshan Feb 21 '11 at 21:28
@razshan: you need to check the state of the checkboxes when the button is clicked, not when the checkboxes are checked – ide Feb 21 '11 at 21:51
@ide, thanks. even then its not working. I used the second option – razshan Feb 21 '11 at 22:07
For booleans, `^` is in fact equivalent to `!=` (apart from the difference in priority) – Paŭlo Ebermann Feb 21 '11 at 23:25

Matti Virkkunen · Answer 2 · 2011-02-21T20:40:20.613

5

You can use the != operator. For two booleans it has the same truth table as an "actual" XOR operator.

edited Feb 21 '11 at 20:40

answered Feb 21 '11 at 20:22

Matti Virkkunen

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You seem to indicate that `^` wouldn't work for boolean expressions. – aioobe Feb 21 '11 at 20:37
@aioobe: I removed that part. I had no idea it could be used with booleans as well. – Matti Virkkunen Feb 21 '11 at 20:40

score 4 · Answer 3 · answered Feb 21 '11 at 20:31

As pointed out in other answers, the xor operator for boolean (and bitwise) expressions is ^.

boolean a = true;
boolean b = false;

boolean c = a ^ b;  // c == true

(It should also be noted that & and | works just fine for boolean expressions too.)

So, why does && and || exist, but not ^^?

The explanation is evident if you consider the difference between & and &&.

The first one (&) does not short-circuit the evaluation, while && does. So logically, ^^ would correspond to the short circuited version of ^. But, there is no way ^ can be short-circuited (no matter what the first operand evaluates to, the second operand needs to be evaluated) so ^^ would be completely redundant.

score 2 · Answer 4 · answered Feb 21 '11 at 20:22

2

^ is the boolean logical exclusive OR

answered Feb 21 '11 at 20:22

Nanne

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3

@SLaks: its called a "boolean logical" XOR numerous times... For booleans its the XOR. So while it is bitwise, the 'no' is a bit quick, isn't it? – Nanne Feb 21 '11 at 20:25

score 1 · Answer 5 · answered Feb 21 '11 at 20:22

1

All of Java's operators, including XOR.

http://download.oracle.com/javase/tutorial/java/nutsandbolts/operators.html

answered Feb 21 '11 at 20:22

Mike Yockey

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score 1 · Answer 6 · answered Feb 21 '11 at 20:25

1

Way to go

boolean xor = a ^ b;

answered Feb 21 '11 at 20:25

vidstige

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score 0 · Answer 7 · answered Feb 21 '11 at 20:24

0

You can do it the long way. This is a logical XOR.

!(p && q) && (p || q)

answered Feb 21 '11 at 20:24

user489041

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score 0 · Answer 8 · edited May 23 '17 at 12:08

0

You use the ^ character.

See Creating a "logical exclusive or" operator in Java

edited May 23 '17 at 12:08

Community

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answered Feb 21 '11 at 20:28

mrtom

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Logical expressions in java

8 Answers8