Calling method that exists in child classes but not in parent class

Question

public class Parent {
    ....
}

public class Child1 extends Parent {
    ....
    public void foo() {
        ....
    }
}

public class Child2 extends Parent {
           


        

Answer 1

You can't do it with parent object reference until an unless method is declared in parent class/interface itself.

You have to downcast it to child class because parent class/interface doesn't have any knowledge about the child class other than the contract defined between them.

Here contract means abstract methods.

---

you can try in this way where there is no need to put a check it.

FooInterface sc =new Child1();
sc.foo();

...

interface FooInterface{
    void foo();
}

public class Parent {

}

public class Child1 extends Parent implements FooInterface{

    public void foo() {

    }
}

public class Child2 extends Parent implements FooInterface{

    public void foo() {

    }
}