Java 8 – Lambda Expression example

Lambda Expression

Lambda expression is a new feature in Java 8 .
Alternative to anonymous class implementation of interfaces ( with single abstract method ).
syntax : (parameters) -> { body of statements }

Example – Sorting the list of Employees using comparator

Lets use the following employee class objects for adding to the list.

public class Employee {
 private String name;
 private int salary ;

 public Employee(String name, int salary ) {
  this.name = name;
  this.salary = salary;
 }

 public String getName() {
  return name;
 }

 public int getSalary() {
  return salary;
 }
}

public class Employee {

private String name;

private int salary ;

public Employee(String name, int salary ) {

this.name = name;

this.salary = salary;

}

public String getName() {

return name;

}

public int getSalary() {

return salary;

}

Old way ( before Java 8 )

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class ExampleWithoutLambdaExp{
 public static void main(String[] args) {

  List list = new ArrayList() ;
  list.add(new Employee("Naveen",1000));
  list.add(new Employee("Hari",2000));
  list.add(new Employee("Raju",9000));

  // sort by name using anonymous class implementation of Comparator ( interface having single method )
  Collections.sort(list, new Comparator() {
    @Override
    public int compare(Employee e1, Employee e2) {
     return e1.getName().compareTo(e2.getName());
    }
  });

  System.out.println("Sorted by Name :");
  for (Employee employee : list) {
    System.out.println("Name : " + employee.getName() + " , Salary : " + employe    e.getSalary());
  }
 }
}

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

public class ExampleWithoutLambdaExp{

public static void main(String[] args) {

List list = new ArrayList() ;

list.add(new Employee("Naveen",1000));

list.add(new Employee("Hari",2000));

list.add(new Employee("Raju",9000));

// sort by name using anonymous class implementation of Comparator ( interface having single method )

Collections.sort(list, new Comparator() {

@Override

public int compare(Employee e1, Employee e2) {

return e1.getName().compareTo(e2.getName());

}

});

System.out.println("Sorted by Name :");

for (Employee employee : list) {

System.out.println("Name : " + employee.getName() + " , Salary : " + employe e.getSalary());

}

Using Lambda expression ( available from Java 8 )

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class ExampleWithLambdaExp {
 public static void main(String[] args) {

  List list = new ArrayList() ;
  list.add(new Employee("Naveen",1000));
  list.add(new Employee("Hari",2000));
  list.add(new Employee("Raju",9000));

  // sort by name using lambda expression.Using lambda expression for creating the object of comparator. 
  // Compiler automatically knows that the second parameter (object formed by lambda exp) is of type Comparator       with the help of sort() declaration.
  Collections.sort(list, (e1,e2) -> e1.getName().compareTo(e2.getName()));

  System.out.println("Sorted by Name :");
  for (Employee employee : list) {
    System.out.println("Name : " + employee.getName() + " , Salary : " + employe     e.getSalary());
  }
 }
}

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

public class ExampleWithLambdaExp {

public static void main(String[] args) {

List list = new ArrayList() ;

list.add(new Employee("Naveen",1000));

list.add(new Employee("Hari",2000));

list.add(new Employee("Raju",9000));

// sort by name using lambda expression.Using lambda expression for creating the object of comparator.

// Compiler automatically knows that the second parameter (object formed by lambda exp) is of type Comparator with the help of sort() declaration.

Collections.sort(list, (e1,e2) -> e1.getName().compareTo(e2.getName()));

System.out.println("Sorted by Name :");

for (Employee employee : list) {

System.out.println("Name : " + employee.getName() + " , Salary : " + employe e.getSalary());

}

Output

Sorted by Name :
Name : Hari , Salary : 2000
Name : Naveen , Salary : 1000
Name : Raju , Salary : 9000

References

Java 8 – new features and enhancements with examples

http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/Lambda-QuickStart/index.html