JavaFX Assigning action to all buttons in an array of arrays using for-loop

Question

We have this warm up exercise where we're supposed to create this reallllly simple game which's UI is pretty much set up

which's UI is pretty much set up .

I got the error "Local variable i defined in an enclosing scope must be final or effectively final".

I didn't understand it, so I googled it, but most of the problems are different. While typing this question I found this in the stackoverflow suggestions:

Assigning an action to each button, in an array of buttons in JavaFX

But I simply don't understand. I'm learning programming/java from scratch. I hope JavaFX/GuI stuff isn't a hindrance?

The code below only includes my attempt to assign the actions. I separated it from the creation of the buttons for the time being to figure out what the problem is. The problem is only in the if and else conditions.

    for(int i=0; i<=4; i++) {

        for(int j=0; j<=4; j++) {

            buttonGrid[i][j].setOnAction(new EventHandler<ActionEvent>() {
                public void handle(ActionEvent event) {
                    
                    if (buttonGrid[i][j].getText() == "X") {
                        buttonGrid[i][j].setText("O");
                    } else {
                        buttonGrid[i][j].setText("X");
                    }
                }
            });
         }
    }

For now I just want the button's labels to change from X to O and from O to X as you click them. Btw. If I learn JavaFX and GUI, does it mean I HAVE to learn css? (Not that I don't want to, just.. not now)

If there is a need for the rest of the code to figure the problem: http://textuploader.com/5b1kh

I'd also appreciate if someone could tell me how to do the Scenes in a more efficent way. (Btw, can I somehow lock the aspect ratio of the sides of all cells of a gridpane?)

The error is because variables are copied inside an anonymous class and so has to be final. Better explanation here :stackoverflow.com/questions/4732544/… — Vivin
– Vivin, Commented May 10, 2016 at 4:56

Community · Accepted Answer · 2017-05-23 11:59:52Z

1

I think that the answer in this question explains your problem very well and how to solve it Problems with local variable scope. How to solve it? You can not use i and j inside the Action handler.

Try this. [Notice that I've also changed the string comparison*]

 for(int i=0; i<=4; i++) {

    for(int j=0; j<=4; j++) {

        final Button myButton = buttonGrid[i][j];

        myButton.setOnAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent event) {
                if ("X".equals(myButton.getText())) {
                    myButton.setText("O");
                } else {
                    myButton.setText("X");
                }
            }
        });
    }
}

[*] How do I compare strings in Java?

edited May 23, 2017 at 11:59

CommunityBot

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answered May 10, 2016 at 4:56

RubioRic

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2 Comments

Duc Nguyen Over a year ago

Thank you very much! I got it to work, but I used Button, idk what JButton is and I kept my String comparison, because yours for some reason gave me a Syntax error, although there should be none.. edit: nvm there was just a bracket missing

RubioRic Over a year ago

@HenryLa You're welcome. JButton is a Swing class. More or less the previous version of JavaFx. My mistake. Mark the answer as accepted if it has been useful, please.

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