How do I use super in java?

public class A {

public void foo() {
System.out.println("A's foo");
    }
}



public class B extends A {
    public void foo() {
    System.out.print("B's foo");
    }
}



public  class Test1 {
public static void main(String[] args){
 开发者_StackOverflow   A a= new B();
    a.foo();
  }
}

I want to use A's foo, what is the syntax for doing that? I tried a.super.foo();.

Thank you

You can only do so from within the class B. You won't be able to invoke A's foo from outside A or B classes.

A a= new B(); will always set the reference a to an instance of B. Thus, even though you cast it to A, at runtime the method that gets invoked is B.foo. That's runtime polymorphism.

I am really uneasy about a design that needs to do this kind of thing. If you want the object to behave like an A, why did you create a B?

You cannot use super from the outside of the class. Assuming you really, really need this (but I really doubt you can't find a better way) the best you can do about it is to expose a method that does this call to the outside:

public class B extends A {
    public void super_foo() {
        super.foo();
    }
    public void foo() {
        System.out.print("B's foo");
    }
}

public  class Test1 {
    public static void main(String[] args){
        A a= new B();
        a.super_foo();
    }
}

Here is it

    public class A {

    public void foo() {
    System.out.println("A's foo");
        }
    }



    public class B extends A {
        public void foo() {
        super.foo();
        System.out.print("B's foo");
        }
    }



public  class Test1 {
public static void main(String[] args){
    A a= new B();
    a.foo();
  }
}

You can't access it. The keyword is that it has been overridden by Java so it's no longer accessible.

What you want to achieve will work if the method is static. Non virtual methods in java

public class A {
    public static void foo() {
        System.out.println("A's foo");
    }
}

public class B extends A {
    public static void foo() {
        System.out.print("B's foo");
    }
}

public  class Test1 {
    public static void main(String[] args){
       A a= new B();
       a.foo();
    }
}