Java Programming Techniques and APIs

Lambda Expression in Java

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Lambda Expression in Java

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Introduction

In Java SE 8, an important and new feature was introduced Lambda Expressions. Using an expression provides a clear and brief way to express method interfaces. It does help in the collection library as it helps in iterating, filtering and extracting data from a collection.

The compiler doesn’t create a .class file because lambda expression is handled as a function.

Functional Interface

The Functional interface is an interface that only has one abstract method. To declare a functional interface, java provided an annotation i.e. @FunctionalInterface. Lambda expressions give the implementation of a functional interface.

Benefits of Lambda Expression

  • Handles the functionality as a method argument or code as data. It saves a lot of code. We do not need to define the method again, for the implementation part, here we just need to type out the implementation code.
  • When needed lambda expression can be used as an object and can also be passed around.
  • Not being in any class, a function can be created.
  • Also gives the implementation of a functional interface.

Java Lambda Expression Syntax

(argument-list) -> {body} 

Java lambda expression has three components.

  1. Argument list: It is empty and also can be non-empty.
  2. Arrow-token: The arrow token is used to link the body expressions with the arguments list.
  3. Body: It has the statements for the lambda expressions.

No parameter syntax

() -> { 
//Body
}

One Parameter Syntax

(p1) -> {
//Body
} 

Two Parameter Syntax

(p1,p2) -> {
//Body
} 

No Parameter Java Lambda Expression

Code

interface Interface{
    public String print(); 
} 
public class main{ 
  public static void main(String[] args) { 
    Interface s=()->{ 
        return "Hello User"; 
    }; 
    System.out.println(s.print()); 
  } 
} 

Output

Hello User

write your code here: Coding Playground

Single Parameter Java Lambda Expression

Code

interface Interface{ 
    public String print(String name); 
} 
 
public class main{ 
    public static void main(String[] args) { 
     
        // Single parameter. 
        Interface I1=(name)->{ 
            return "Hey, "+name; 
        }; 
        System.out.println(I1.print("User")); 
         
        // Function parentheses omitted
        Interface I2= name ->{ 
            return "Hey, "+name; 
        }; 
        System.out.println(I2.say("User"));
    } 
}  

Output

Hey User
Hey User

write your code here: Coding Playground

Multiple Parameters Java Lambda Expression

Code

interface add{ 
    int calc(int x,int y); 
} 
 
public class main{ 
    public static void main(String[] args) { 
         
        // Multiple parameters 
        add a1=(x,y)->(x+y); 
        System.out.println(a1.calc(10,20)); 
         
        // Multiple parameters
        add a2=(int x,int y)->(x+y); 
        System.out.println(a2.calc(100,200)); 
    } 
}  

Output

30
300

write your code here: Coding Playground

For each loop using Java Lambda Expression

Code

import java.util.*; 
public class main{ 
    public static void main(String[] args) { 
         
        List<String> l=new ArrayList<String>(); 
        list.add("l1"); 
        list.add("l2"); 
        list.add("l3"); 
        list.add("l4"); 
         
        list.forEach( 
            (x)->System.out.println(x) 
        ); 
    } 
}  

Output

l1
l2
l3
l4

write your code here: Coding Playground

Multiple Statements Java Lambda Expression

Code

@FunctionalInterface 
interface Interface{ 
    String print(String s); 
} 
 
public class main{ 
    public static void main(String[] args) { 
     
        // Passing multiple statements 
        Interface I = (s)-> { 
            String s1 = "Hello "; 
            String s2 = str1 + message;  
            return s2; 
        }; 
            System.out.println(I.print("World! ")); 
    } 
}  

Output

Hello World!

write your code here: Coding Playground