Question

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Why Java does not see that Integers are equal?

I have 2 integers that I assign from the same argument.

One of the integers I decrease the value by 1 then increment the value by 1.

When I compare them again they are not always equal.

This is from my book, can someone please explain, I cannot understand my books explanation.

class Test{

    public static void main(String[] args){
        Integer i = Integer.parseInt(args[0]);
        Integer j = i;
        System.out.println("1:" + i + ", j:" + j);
        i--;
        System.out.println("2:" + i + ", j:" + j);
        i++;
        System.out.println("3:" + i + ", j:" + j);
        System.out.println((i==j));

    }
}

Output:
Input 256 as argument

1:256, j:256
2:255, j:256
3:256, j:256
false

Thank you for your consideration.

Answer 1

You are comparing two references that are not the same because of the ++– (New Objects Created). The way to compare two Integer objects equals() method. equals() will check Integer’s inner state. Check this code:

    Integer i = 256;
    Integer j=i;
    System.out.println(i==j);         //True  (Because we are pointing the same object)
    i--;
    i++;        
    System.out.println(i==j);         //False (Because reference has changed)
    System.out.println(i.equals(j));  //True  (Because the inner state is the same)