What is binary compatibility in Java?

Question

I was reading Effective Java by Joshua Bloch.

In Item 17: \"Use interfaces only to define types\", I came across the explanation where it is not advised to use Inte

Answer 1

If in future, we wish to change the interface that some classes are implementing (e.g., addition of some new methods).

If we add abstract methods(additional methods), then the classes (implementing the interface) must implements the additional method creating dependency constraint and cost overhead to perform the same.

To overcome this, we can add default methods in the interface.

This will remove the dependency to implement the additional methods.

We do not need to modify the implementing class to incorporate changes. This is called as Binary Compatibility.

Please refer the example below:

The interface that we are going to use

    //Interface       
    interface SampleInterface
            {
                // abstract method
                public void abstractMethod(int side);

                // default method
                default void defaultMethod() {
                   System.out.println("Default Method Block");
                }

                // static method
                static void staticMethod() {
                    System.out.println("Static Method Block");
                }
            }


//The Class that implements the above interface.

    class SampleClass implements SampleInterface
    {
        /* implementation of abstractMethod abstract method, if not implemented 
        will throw compiler error. */
        public void abstractMethod(int side)
        {System.out.println(side*side);}

        public static void main(String args[])
        {
            SampleClass sc = new SampleClass();
            sc.abstractMethod(4);

            // default method executed
            sc.defaultMethod();

            // Static method executed
            SampleInterface.staticMethod();

        }
    }

Note: For more detailed information, please refer default methods