Create a compareTo to a Generic Class that Implements Comparable

Question

I have a Generic Class with two type variables, which implements java.lang.Comparable.

public class DoubleKey implements Comparable

        

Answer 1

public class DoubleKey<
        K implements Comparable, 
        J implements Comparable> 
    implements Comparable> {

    public int compareTo(DoubleKey that){
        int cmp = this.key1.compareTo(that.key1);
        if(cmp==0) cmp = this.key2.compareTo(that.key2);
        return cmp;
    }
}