Late Binding in Java

Question

I have searched through all the similar questions on late binding on stack overflow, and I would severely disagree with anyone who marks this question as a duplicate. First off, i found this example on another question, but I do not understand how I am supposed to know when something is decided during compile time and when something is decided during run time. Basically, the crux of my question boils down to two things:

• What in this example must bring me to the logical conclusion that one method is late binding and another is early binding

• How do I know when the decision about which version of a method to execute is decided during run-time or compile time in Java

Code:

class A
{
    public void foo()
    {
        System.out.println("Class A");
    }
}

class B extends A
{
    public void foo()
    {
        System.out.println("Class B");
    }
}

public class C
{
    public static void main(String [] args)
    {
        A a=new A();
        B b=new B();
        A ref=null;

        /* 
            early binding  --- calls method foo() of class A and
            decided at compile time
        */ 
         a.foo(); 

        /* early binding --- calls method foo() of class B and
            decided at compile time
        */
          b.foo(); 

        /* late  binding --- --- calls method foo() of class B and
           decided at Run time
     */ 
        ref=b;
        ref.foo(); }
}

Answer 1

Wrong on all counts. The method to be called is decided at runtime, in every case here, based on the runtime type of the object. The only decisions made at compile time are for calls to final, private, or static methods, or choices among a set of overloaded methods (which could still lead to runtime choices if the overloaded methods are not final, private, or static.)