Lambda Expressions

Now the lambda expressions are also introduced in JAVA 8 and it is praised as the biggest attribute of Java 8. These lambda expressions make functional programming smooth and clarify the upgradation path a lot.

Syntax

The lambda expression is identified by the following Syntax:

Below are the important characteristics of a lambda expression.

• Optional type declaration − You don’t need to announce the sort of a parameter. The compiler can inference an equivalent from the worth of the parameter.
• Optional parentheses parameter − You don’t need to announce one parameter in parenthesis. For multiple parameters, parentheses are required.
• Curly braces are unforced now − There is no need to use curly braces in the expression body if the body contains one statement.
• Optional return keyword − The compiler automatically returns the worth if the body features a single expression to return the worth. Curly braces are required to point that expression returns a worth.

Example of Lambda Expressions:

You have to create the below given Java Program by using any editor of your choice in, say C:\> JAVA.

Java8Tester.java

public class Java8Tester {
   public static void main(String args[]) {
      Java8Tester tester = new Java8Tester();
      //with type declaration
      MathOperation addition = (int a, int b) -> a + b;
      //with out type declaration
      MathOperation subtraction = (a, b) -> a - b;
      //with return statement along with curly braces
      MathOperation multiplication = (int a, int b) -> { return a * b; };
      //without return statement and without curly braces
      MathOperation division = (int a, int b) -> a / b;
      System.out.println("10 + 5 = " + tester.operate(10, 5, addition));
      System.out.println("10 - 5 = " + tester.operate(10, 5, subtraction));
      System.out.println("10 x 5 = " + tester.operate(10, 5, multiplication));
      System.out.println("10 / 5 = " + tester.operate(10, 5, division));
      //without parenthesis
      GreetingService greetService1 = message ->
      System.out.println("Hello " + message);
      //with parenthesis
      GreetingService greetService2 = (message) ->
      System.out.println("Hello " + message);
      greetService1.sayMessage("Mahesh");
      greetService2.sayMessage("Suresh");
   }
   interface MathOperation {
      int operation(int a, int b);
   }
   interface GreetingService {
      void sayMessage(String message);
   }
   private int operate(int a, int b, MathOperation mathOperation) {
      return mathOperation.operation(a, b);
   }
}

Verify Your Result

Assemble the class using javac compiler as follows-

C:\JAVA>javac Java8Tester.java

Now it's time to Run the Java8 tester as given below-

C:\JAVA>java Java8Tester

Your output should be like this:-

10 + 5 = 15
10 - 5 = 5
10 x 5 = 50
10 / 5 = 2
Hello Mahesh
Hello Suresh

Following are the details 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 one method only. In the given example, we have used many kinds of lambda expressions to explain the operation method of the MathOperation interface. Then we've to interpret the implementation of sayMessage of GreetingService.
• Lambda expression eliminates the necessity of anonymous class and provides a really simple yet powerful functional programming capability to Java.

Scope

Using lambda expression, you'll ask any final variable or effectively final variable (which is assigned only once). Sometimes Lambda expressions direct a compilation error, if a variable is assigned a value the second time.

Scope Example

Create the subsequent Java program using any editor of your choice in, say, C:\> JAVA

Java8Tester.java

public class Java8Tester {
   final static String salutation = "Hello! ";
  
   public static void main(String args[]) {
      GreetingService greetService1 = message -> 
      System.out.println(salutation + message);
      greetService1.sayMessage("Mahesh");
   }
   interface GreetingService {
      void sayMessage(String message);
   }
}

Confirm the Result

Assemble the class using the javac compiler as given below-

C:\JAVA>javac Java8Tester.java

Now you have to run the Java8Tester same as given below:

C:\JAVA>java Java8Tester

Your output must look like this:

Hello! Mahesh