Android / Java: For loop preventing array from being called

Question

I am making a 3x3 grid type application, and I want to recall the button pressed to change it by adding a for loop. However, I get the exception "java.lang.ArrayIndexOutOfBoundsException: length=3; index=3" because the for loop is weird. Could anyone figure out this for me? I am new to java and programming in general.

Code:

public int j = 1;
public int i = 1;
public final int[][] buttons = new int[][] {
        {R.id.top_left_button, R.id.top_center_button, R.id.top_right_button},
        {R.id.left_button, R.id.center_button, R.id.right_button},
        {R.id.bottom_left_button, R.id.bottom_center_button, R.id.bottom_right_button}};
private Button lastButton;

public void setPlayer(Button button, int x, int y){
    button.setText("!");
    lastButton = (Button)findViewById(buttons[x][y]);
    lastButton.setText(" ");
    lastButton = button;
}
@Override


protected void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_game);


    ctx = this;

    final GameEngine game = new GameEngine();
    lastButton = (Button)findViewById(R.id.center_button);
    for (i = 0; i < buttons.length; i++) {
        for (j = 0; j < buttons[i].length; j++) {
            final Button button = (Button)findViewById(buttons[i][j]);
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Button b = (Button)v;
                    int x = i;
                    int y = j;
                    setPlayer(b, x , y);
                }
            });
        }
    }

Try this public final int[][] buttons = new int[3][3] now assign id's to array . — sonus21
– sonus21, Commented Jan 15, 2015 at 3:37
I have read that answer but your comment says something different. Putting size is not necessary when you are assigning value right then — Rohit5k2
– Rohit5k2, Commented Jan 15, 2015 at 4:26

Andrew Shepherd · Accepted Answer · 2015-01-15 03:49:42Z

3

The question you need to ask is: what are the values of i and j when the button is clicked?

The answer for i is: buttons.length. Because that's the value you left i at when you left the loop.

This should work:

for (i = 0; i < buttons.length; i++) {
        final int iCopy = i;  
        for (j = 0; j < buttons[i].length; j++) {
            final Button button = (Button)findViewById(buttons[i][j]);
            final int jCopy = j;
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Button b = (Button)v;
                    int x = iCopy;
                    int y = jCopy;
                    setPlayer(b, x , y);
                }
            });
        }
    }

The reason this will work is, because of the scoping, you are creating a new instance of iCopy with each outer iteration, and a new instance of jCopy with each inner iteration. Each anonymous OnClickListener implementation will now be using the appropriate copies.

edited Jan 15, 2015 at 3:49

answered Jan 15, 2015 at 3:42

Andrew Shepherd

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1 Comment

trungdinhtrong Over a year ago

Good catch! However, IMO, a better solution is to declare i and j as local variable unless the value of i and j is used later, which I very much doubt

Tim Ashton · Accepted Answer · 2015-01-15 03:44:45Z

1

You should declare and initialize your array like this:

public final int[][] buttons = {
        {R.id.top_left_button, R.id.top_center_button, R.id.top_right_button},
        {R.id.left_button, R.id.center_button, R.id.right_button},
        {R.id.bottom_left_button, R.id.bottom_center_button, R.id.bottom_right_button}};

In your loops you can just initalize new i and j variables like this:

for (int i = 0; i < buttons.length; i++) {
    for (int j = 0; j < buttons[i].length; j++) {
    ...
    ...
    }
}

No need to declare them at the top of your activity.

answered Jan 15, 2015 at 3:44

Tim Ashton

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