Lambda Expressions

Lambda expressions are presented in Java 8 and are touted to be the greatest component of Java 8. Lambda expression facilitates functional programming, and simplifies the development a lot.

A lambda expression is characterized by the following syntax −

parameter -> expression body

Following are the important characteristics of a lambda expression −

• Optional type declaration − No need to declare the type of a parameter. The compiler can inference the same from the value of the parameter.

• Optional parenthesis around parameter − No need to declare a single parameter in parenthesis. For multiple parameters, parentheses are required.

Lambda Expressions Example

Create the following Java program using editor and save in some folder like com.mindclues.java8

Java8Lambda.java

package com.prejava.java8

public class Java8Lambda {
   public static void main(String args[]){
      Java8Lambda lamb = new Java8Lambda();
        
      //with type declaration
      MathOperation add = (int a, int b) -> a + b;
        
      //without type declaration
      MathOperation subtract = (a, b) -> a - b;
        
      //with return statement along with curly braces i.e."{ }"
      MathOperation multiply = (int a, int b) -> { return a * b; };
        
      //without return statement and without curly braces
      MathOperation divide = (int a, int b) -> a / b;
        
      System.out.println("20 + 5 = " + lamb.operate(20, 5, add));
      System.out.println("20 - 5 = " + lamb.operate(20, 5, subtract));
      System.out.println("20 x 5 = " + lamb.operate(20, 5, multiply));
      System.out.println("20 / 5 = " + lamb.operate(20, 5, divide));
        
      //with parenthesis
      Greetings greetings1 = message ->
      System.out.println("Hi!! " + message);
        
      //without parenthesis
      Greetings greetings2 = (message) ->
      System.out.println("Hi!! " + message);
        
      greetings1.greet("Suresh");
      greetings2.greet("Ramesh");
   }
  
   private int operate(int a, int b, MathOperation mathOperation){
      return mathOperation.operation(a, b);
   }
}

MathOperation.java

package com.prejava.java8
interface MathOperation {
    int operation(int a, int b);
 }

Greetings.java

package com.prejava.java8
interface Greetings {
    void greet(String message);
 }

Verify the Result

Compile the class using javac compiler as follows −

$javac Java8Lambda.java

Now run the Java8Tester as follows −

$java Java8Lambda

It should produce the following output −

20 + 5 = 25
20 - 5 = 15
20 x 5 = 100
20 / 5 = 4
Hi!! Suresh
Hi!! Ramesh

Following are the important points to be considered in the above example.

• Lambda expressions are used primarily to define inline implementation of a functional interface, i.e., an interface with a single method only. In the above example, we've used various types of lambda expressions to define the operation method of MathOperation interface. Then we have defined the implementation of greet of Greetingings.

• Lambda expression eliminates the need of anonymous class and gives a very simple yet powerful functional programming capability to Java.

Scope

Using lambda expression, you can refer to final variable or effectively final variable (which is assigned only once). Lambda expression throws a compilation error, if a variable is assigned a value the second time.

Scope Example

Create the following Java program using editor and save in some folder like com.prejava.java8

Java8Tester.java

public class Java8Lambda {

   final static String salutation = "Hi!! ";
   
   public static void main(String args[]){
      Greetings greetings1 = message -> 
      System.out.println(salutation + message);
      greetings1.greet("Suresh");
   }

Greetings.java

   interface Greetings {
      void greet(String message);
   }
}

Verify the Result

Compile the class using javac compiler as follows −

$javac Java8Lambda.java

Now run the Java8Lambda as follows −

$java Java8Lambda

It should produce the following output −

Hi!! Suresh