Java Covariants

Question

public class CovariantTest {
    public A getObj() {
        return new A();
    }

    public static void main(String[] args) {
        CovariantTest c = new SubCov         


        

Answer 1

I was looking at your code and was having some trouble compiling it. Getting error

The return type is incompatible with CovariantTest.getObj()

I made a small change.

class A {
    int x = 5;
}

class B extends A {
    int x = 6;
 }

public class CovariantTest {

    public A getObj() {
        return new A();
    }

    public static void main(String[] args) {
        CovariantTest c = new SubCovariantTest();
        A a = c.getObj();

        System.out.println(c.getObj().x);
    }
}

 class SubCovariantTest extends CovariantTest {
    public A getObj() {
        return new B();
    }

 }

Stick a breakpoint in at the system out line and look at the a variable. It contains two x members, with one set to 5 and one to 6.

Starblue's answer explains this behaviour.