Question

I want to write a java program which has to find the differences between the two objects which is of different instances. I have implemented it using equals() and comparator. But here I want to find differences and have to show that in logging format.

My program is below :

public class A implements Comparator<A>{

private int id1, id2;

/* setters and getters for id1 and id2 */

     public boolean equals(Object arg0) {
    if (this.getClass() != arg0.getClass()) {
        return false;
        }

        if (((A) arg0).getId1() == this.id1 && ((A) arg0).getId2() == this.id2) {
        return true;
        }

        return false;
     }

 public static void main(String args[]) {

    A obj1 = new A();
    obj1.id1 = 10;
    obj1.id2 = 20;

    A obj2 = new A();
    obj2.id1 = 30;
    obj2.id2 = 20;

    /*
     * equals comparison
     */

    if (obj1.equals(obj2)) {
        System.out.println("EQUALS");
    } else {
        System.out.println("NOT EQUALS");
    }

}

Please can any body advise me how i can find the differences and show that in logging format.

Thanks.

Answer 1

To implement Comparator<A> you need a method public int compare(A o1, A o2). This is an example of such an implementation:

@Override
public int compare(A o1, A o2) {
    if (o1 == o2) {
        return 0;
    } else if (o1 == null) {
        return -1;
    } else if (o2 == null) {
        return 1;
    }
    if (o1.getId1() != o2.getId1()) {
        return o1.getId1() - o2.getId1();
    } else {
        return o1.getId2() - o2.getId2();
    }
}

Then you can use it like this:

    if (obj1.compare(obj1, obj2) == 0) {
        System.out.println("EQUALS");
    } else {
        System.out.println("NOT EQUALS");
    }

It is probably more common to make another class implement the Comparator<A>, instead of putting this in A itself.