What’s new in Java 8

Let’s have a brief look at these Java 8 features. I will provide some code snippets for better understanding the features in a simple way.

Some of the important Java 8 features are;

1. Lambda expressions
2. Method references
3. Functional Interfaces

1. Lambda expressions

• Lambda expression helps us to write our code in a functional style.
• These are just like functions and they accept parameters just like functions.
• It is an anonymous function, no function name and no method return type.
• The body of a lambda expression can contain zero, one or more statements.
• It saves a lot of code, we don’t need to define the method again for providing the implementation.

Syntax:

  lambda operator -> body

Example:

    () -> System.out.println("lambda expression simplest example");

2. Method references

• Method reference is used to refer to a method of functional interface.
• It is a compact and easy form of lambda expression.
• Each time when you are using lambda expression to just refer to a method, you can replace your lambda expression with method reference.

Types of method References are given below:-

1. Method reference to static method

      	@FunctionalInterface 
		public interface Walkable{  
    		public abstract void walk();  
		}  
            
            public class Sample { 
               public static void walking() {
            		System.out.println(“Hey, lets go to walk”);
 			}
 

          }

		public class MainClass {  
    		public static void main(String[] args) {  
        	
            //Lambda Expression
        	//Walkable walkable=()->System.out.println(“Hey, lets go to walk”);
            
		// Replaced above Lambda Expression with Method Reference
            Walkable walkable=Sample::walking;
            walkable.walk();

    		  }  
	    }

Output:

Hey, lets go to walk

2. Method reference to instance method of a particular object

 	@FunctionalInterface 
		public interface Welcome{  
    		String welcome(String name);  
		}  
            
            public class Sample { 
               public String welcomeMessage(String name) {
            		return “Hey:” + name;
 			}
 

          }

		public class MainClass {  
    		public static void main(String[] args) {  
        	
            //Lambda Expression
        	// Welcome welcome2=name -> “Hey:” + name;
            
		// Replaced above Lambda Expression with Method Reference
            Welcome welcome2=new Sample()::welcomeMessage;
            System.out.println(welcome2.welcome(“ABC”));

    		  }  
	    }

3. Method reference to an instance method from class Type

	public class Main {
    		public static void main(String[] args) {
       		 List<String> nameList=new ArrayList<>();

        		nameList.add("John");
        		nameList.add("Tony");
        		nameList.add("Abhay");
        		nameList.add("Sam");
      		 nameList.add("Danny");
        
      		  //nameList.sort((s1,s2) -> s1.compareTo(s2));
		
		// Replaced Lambda Expression from above line to Method Reference
        		nameList.sort(String::compareTo);
        		nameList.forEach(System.out::println);

    		}
		}

Output:-

Abhay

Danny

John

Sam

Tony

4. Method reference to Constructor

	@FunctionalInterface 
		public interface Welcome{  
    		public abstract void welcome();  
		}  
            
            public class Sample { 
		//constructor
               Sample() {
            		System.out.println(“Method reference to Constructor”);


 			}
 

          }

		public class MainClass {  
    		public static void main(String[] args) {  
        	
		// Method Reference to constructor
            Welcome welcome2=Sample::new;
            welcome2. Welcome();

    		  }  
	    }

Output:

	   Method reference to Constructor	

3. Functional Interfaces

• An interface which has only one abstract method is called Functional Interfaces.
• In short form, it is also called as SAM interface, which means Single Abstract Method Interface.
• Runnable, ActionListener, Comparable are some of the examples of functional interfaces. 

Why Functional Interface?

• Functional interface is used for enabling functional programming in the java language.
• It is also used for defining Lambda expressions to a function directly as an argument to a method.
• As we define LE from a FI, we can also define a Functional Interface as a Base type/ Super type of a Lambda Expression.

Syntax:-

interface <interface-name> {
				-one abstract method 
			}

Example:

@FunctionalInterface
		   interface Multiply
			{
   			 int cal(int x);
			}

		public class Main {
   			 public static void main(String[] args) {
    			  int a = 5;

        		// lambda expression to define the cal method
       		 Multiply mul = (int x)->x*x;

      		  //parameter passed and return type must be same as defined 			in the prototype
  		      int result = mul.cal(a);
    		    System.out.println(result);

      		  }

Reference

https://beginnersbook.com/2017/10/java-8-features-with-examples/