Creating object with reference to Interface

Question

A reference variable can be declared as a class type or an interface type.If the variable is declared as an interface type, it can reference any object of any class that impleme

Answer 1

The displayName() method is displayed as undefined because objParent declared as type Printable and the interface does not have such method. To be able to use method displayName(), you can declare it in interface Printable:

interface Printable {
    void sysout();
    void displayName();
}

Or cast objParent to type Parent first before calling method displayName():

Printable objParent = new Parent();
objParent = (Parent) objParent;
objParent.displayName();