Question

Let’s consider this example :

public class Shared {

    private int attribute;

    public Shared() {}

    public void incrementAttribute(int i) {
            attribute += i;
    }

    public int getAttribute() {
            return attribute;
    }

    public static void main(String[] args) {
            Shared s1 = new Shared();
            Shared s2 = new Shared();

            s1.incrementAttribute(1);
            s2.incrementAttribute(1);

            s1.getAttribute();
            s2.getAttribute();
    }    
}

How can I change this class to have 1 2 in output when calling getAttribute() and not 1 1

Something like a global variable, I tried the final keyword but I can’t set something using a Method.

Answer 1

You need to make the attribute static.

private static int attribute;
        ^^^^^^

Members that are declared static will be shared between all instances of the class.

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Also, for it to output 1 2 you need to change

s1.incrementAttribue(1);
s2.incrementAttribue(1);

System.out.println(s1.getAttribute());
System.out.println(s2.getAttribute());

to

s1.incrementAttribue(1);
System.out.println(s1.getAttribute());

s2.incrementAttribue(1);
System.out.println(s2.getAttribute());

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ideone.com demonstration