How to get and compare integer array from a list in a list? [duplicate]

Question

I have a program that uses a java.awt robot to get a picture of the screen and then cycle through the pixels and categorize certain colors in blocks in a list of lists of integer arrays. I have a List<List<int[]>> blocks. The first List is a list of all the blocks, the second list is a list of all the pixels in the blocks, and the integer array is 2 value that are the x and y of the pixel. I first tried to use a for loop through all the blocks with list.contain's to find the array, but that always returned false. I am trying now to use a loop like this to find them.

boolean continuer = false;
boolean found = false;
for (List<int[]> thisBlock : blocks) {
    int[] newInt = new int[2];
    newInt[0] = i;
    newInt[1] = j;
    for (int[] thisInt : thisBlock) {
        if (thisInt == newInt) {
            continuer = false;
            found = true;
            System.out.println("Found pixel in block");
            break;
        }
        if (found) {
            break;
        }
    }
    if (found) {
        break;
    }
}
if (!found) {
    continuer = true;
}

This also returned false always. Any help would be greatly appreciated.

You don't compare arrays like this: thisInt == newInt. That tests if two array references point to the same array. See stackoverflow.com/questions/14897366/…. (But in that context, I don't think you should be comparing arrays at all. You should be comparing the array contents with i and j.) — Stephen C
– Stephen C, Commented May 22, 2021 at 3:55
You also have a redundant test. And the continuer logic looks weird to me. — Stephen C
– Stephen C, Commented May 22, 2021 at 3:57
As a meta-suggestion, I suggest you read rubberduckdebugging.com ... and apply those ideas to your approach to debugging your own code. — Stephen C
– Stephen C, Commented May 22, 2021 at 4:01
@StephenC I have an if continuer after that that runs a whole other code that works find, sorry for the inconvenience. — Charlotta16
– Charlotta16, Commented May 22, 2021 at 4:04
I don't understand what you just said there. But the main problem in your code is per my first comment. 1) That's the wrong way to compare arrays by value, and 2) you probably should be comparing arrays by value anyway. — Stephen C
– Stephen C, Commented May 22, 2021 at 4:06

Satwik · Accepted Answer · 2021-05-22 07:32:55Z

1

Arrays cannot be compared with == operator. There are methods that Arrays Class provides to perform operations on Arrays. Use Arrays.equals(thisInt,newInt) instead of thisInt == newInt

answered May 22, 2021 at 7:32

Satwik

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1 Comment

Stephen C Over a year ago

In this case, the OP shouldn't compare arrays at all. A better solution is if (thisInt[0] == i && thisInt[1] == j) {

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