Question

Why does is print last “I’m a Child Class.” ?

public class Parent
{
    String parentString;
    public Parent()
    {
        System.out.println("Parent Constructor.");
    }

    public Parent(String myString)
    {
        parentString = myString;
        System.out.println(parentString);
    }

    public void print()
    {
       System.out.println("I'm a Parent Class.");
    }
} 

public class Child extends Parent
{
    public Child() {
        super("From Derived");
        System.out.println("Child Constructor.");
    }

    public void print()
    {
       super.print();
       System.out.println("I'm a Child Class.");
    }

    public static void main(String[] args)
    {
        Child child = new Child();
        child.print();
        ((Parent)child).print();
    }
}

Output:

From Derived

Child Constructor.

I'm a Parent Class.

I'm a Child Class.

I'm a Parent Class.

I'm a Child Class.

Answer 1

Because this is an example of polymorphism (late binding). At compile time you specify that the object is of type Parent and therefore can call only methods defined in Parent. But at runtime, when the “binding” happens, the method is called on the object, which is of type Child no matter how it is referenced in the code.

The part that surprises you is why the overriding method should be called at runtime. In Java (unlike C# and C++) all methods are virtual and hence the overriding method is called. See this example to understand the difference.