UpCasting & DownCasting in Java - the F*ck you need to know

UpDownCastDemo.java

package _0UpDownCastJava;

//  https://www.geeksforgeeks.org/upcasting-vs-downcasting-in-java/
public class UpDownCastDemo {

    static class Parent {
        String name;

        void someMetho() {
            System.out.println("yup I'm from Parent! Name: " + name);
        }
    }

    static class Child extends Parent {
        int id;

        @Override
        void someMetho() {
//            super.someMetho();
            System.out.println("yup I'm from Child! Id: " + id);
        }
    }


    public static void main(String[] args) {
        //  1
        //  Upcasting
        Parent p = new Child();
        p.name = "yup";
        /*
        * o/p - yup I'm from Child! Id: 0
        * only if
            @Override
            void someMetho() {
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
        //  and
        /*
        * o/p - yup I'm from Parent! Name: yup
                yup I'm from Child! Id: 0
        * only if
            @Override
            void someMetho() {
                super.someMetho();
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
//        uncomment this
        p.someMetho();

        p.name = "hihi";

        //  2
        //  Explicitly downcasting
        Child child = (Child) p;    //  Explicitly Downcasting
        child.id = 9;

        /*
        * o/p - yup I'm from Child! Id: 9
        * only if
            @Override
            void someMetho() {
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
        //  and
        /*
        * o/p - yup I'm from Parent! Name: hihi
                yup I'm from Child! Id: 9
        * only if
            @Override
            void someMetho() {
                super.someMetho();
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
//        uncomment this
        child.someMetho();

        //  3
        //  implicitly downcasting
//        Child dd = new Parent();    //  implicitly downcasting - compile time error

        //  4
        //  my try
        //  ClassCastException
//        Parent parent = new Parent();
//        Child child1 = (Child) parent;
//        child1.id = 999;
//        child1.someMetho();

        //  5
        //  my try
        Child child2 = new Child();
        Parent parent1 = (Parent) child2;
        parent1.name = "wtf";

        /*
        * o/p - yup I'm from Child! Id: 0
        * only if
            @Override
            void someMetho() {
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
        //  and
        /*
        * o/p - yup I'm from Parent! Name: wtf
                yup I'm from Child! Id: 0
        * only if
            @Override
            void someMetho() {
                super.someMetho();
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
        parent1.someMetho();


        //  6
        Parent parent2 = new Parent();
        /*
        * o/p - yup I'm from Parent! Name: null
        * only if
            @Override
            void someMetho() {
                System.out.println("yup I'm from Child! Id: " + id);
            }
        * */
        parent2.someMetho();
    }
}