interface MyInterface{
   public static int num = 100;
   public void display();
}
public class InterfaceExample implements MyInterface{
   public void display() {
      System.out.println("This is the implementation of the display method");
   }
   public void show() {
      System.out.println("This is the implementation of the show method");
   }
   public static void main(String args[]) {
      MyInterface obj = new InterfaceExample();
      obj.display();
      obj.show(); // how can i call this ?
   }
}

Above is some lines of code , I wanted to know can I call show() method of InterFaceExample class using interface object?. Please help.

CodePudding user response：

You have three options.

1. Add the show method to the interface.
2. Change the type of obj to InterfaceExample.
3. Cast obj when you want to use a method that's only in InterfaceExample, for example ((InterfaceExample) obj).show();

The third option here throws an exception if obj happens not to refer to an object of type InterfaceExample.

CodePudding user response：

You need to have an InterfaceExample reference and not a MyInterface reference. The clean way to achieve that is to not assign the InterfaceExample reference to a MyInterface variable; you're throwing type information away. Use an InterfaceExample variable instead.

Alternatively,if there's some reason you have to have a MyInterface variable, then you can cast to an InterfaceExample. You may or may not need to handle the possible resulting exception.