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Java_8 New - Lambda Expressions

Introduction

Lambda expressions are introduced in Java 8 and are touted to be the biggest feature of Java 8. Lambda expression facilitates functional programming and simplifies the development a lot.

Syntax

A lambda expression is characterised by following syntax.

parameter -> expression body

Following are the important characteristics of a lambda expression.

Optional type declaration - No need to declare type of the parameter. Compiler can inference the same from value of the parameter.
Optional parenthesis around parameter - No need to declare a single parameter in parenthesis. For multiple parameters, parenthesis are required.
Optional curly braces - No need to use curly braces in expression body if body contains a single statement.
Optional return keyword - Compiler automatically returns value if body has a single expression to return the value. Curly Braces are required to indicate that expression returns a value.

Example

Create the following java program 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));

//with parenthesis
GreetingService greetService1 = message ->System.out.println("Hello "+ message);

//without parenthesis
GreetingService greetService2 =(message)->System.out.println("Hello "+ message);

greetService1.sayMessage("aarif");
greetService2.sayMessage("md");
}

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 the result

Compile the class using javac compiler as follows

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester to see the result

C:\JAVA>java Java8Tester

See the result.

10 + 5 = 15
10 - 5 = 5
10 x 5 = 50
10 / 5 = 2
Hello aarif
Hello md

Following are important points to be considered using 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 above example, we've used various types of lambda expressions to define opearation method of MathOperation interface. Then we defined implemenation of sayMessage of GreetingService.
Lambda expression elliminates the need of anonumous class and gives a very simple yet powerful functional programming capability to JAVA.

Variable Scope

In lambda expression, you can refer to any final variable or effectively final variable (which is assigned only once). Lambda expression will throw compilation error if variable is assigned a value second time.

Scope Example

Create the following java program using any editor of your choice in say C:/> JAVA

Java8Tester.java

publicclassJava8Tester{
finalstaticString salutation ="Hello! ";
publicstaticvoid main(String args[]){
GreetingService greetService1 = message ->System.out.println(salutation + message);
greetService1.sayMessage("Mahesh");
}
interfaceGreetingService{
void sayMessage(String message);
}
}