Question

How do I use a public int compareTo method to compare two objects? I need to compare the values within the object to the values of another object to test for greater/less than. So comparing a in 2 objects and b in two objects respectfully.

Test x1 = new Test(9999,9999);
Test x2 = new Test(0,0);

public class Test{
    private int a;
    private int b;

    public Test(){
        a = 0;
        b = 0;
    }


    public Test(int a, int b){
        this.a = a;
        this.b = b;
    }
}

Answer 1

Implements Compareable<T> interface to class Test. Compareable interface is having a single method comapreTo which accepts the object to be compared.

class Test implements Compareable<Test>{
    ...
    @Override
    public int compareTo(Test test) {
        // write logic for compare 
        //a negative integer, zero, or a positive integer as 
        //this object is less than, equal to, or greater than the specified object
        return 0;
    }
}

class Main{
    public static void main(String[] args){
        Test x1 = new Test(9999,9999);
        Test x2 = new Test(0,0);
        int x3 = x1.compareTo(x2);
    }
}

This interface actually imposes a total ordering on the objects in collection of each class that implements it. This ordering is referred to as the class’s natural ordering, and the class’s compareTo method is referred to as its natural comparison method. Which helps Collection of Object to sort in certain order.