Interface In Java 8

Interface :

It is similar to a class in java, instead, with a keyword as interface. 

Interface used as method declaration, not for implementation untill jdk7

Eg:

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Public interface MyInteface { Void m1(String str); Void m2(int i); // But you cannot write as follows in interface /*Void m3(String s){ System.out.println("You cannot write this way. "); }*/ }

Interface in Java-8 :

Java-8 interface can have STATIC & DEFAULT methods, we can also have method implementation from jdk 8 but has to be default

Eg: Before JAVA-8 

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Public interface MyInterface{ Void m1(String str); /* Default void m2(String str){ System.out.println(“Gives an error in prior jav-8 versions. ”); } //Gives you an error */ }

Code In Java-8

Java-8 Functional Interface

Java Functional Interface

If look into some other programming languages like c++, Javascript they are called functional programming languages bcoz, we can write functional and use whenever required.

An interface with only 1 abstract method is called Functional interface.

A new annotation @FunctionalInteface provides us to avoid accidental addition od abstract methods.

Functional interface is long waited and much sought out feature of Java-8 as it enables us to use Lambda expressions to instantiate them.

Being object-oriented is not bad, but when we wanted to implement Runnable we do it as follows

Eg: 

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Runnable r = new Runnable(){ @Override public void run() { System.out.println("My Runnable"); }};

If you notice it, the important logic in under run() method right?

Java-8 lambda expressions allow to help us in writing smaller and cleaner code.

Lambda Expressions:

Lambda expression is way through we can visualize functional programming in java object world.

Objects are base of java prog. Lang. and we can never have a function without an Object

Syntax:  (argument) -> (body)

1	Runnable r1 = () -> System.out.println("My Runnable");

In the above code, Runnable is a functional interface so we can use Lambda.

Since run() has no arguments,  we have no arguments passed.

Advantages of Lambda expressions:

1. Reduced lines of code.
2. Pass method into behaviours
3. High efficiency