In this tutorial, we will see some 11 useful Lambda Expressions examples in Java.
Source Code on GitHub
The source code examples created in this tutorial are hosted on my GitHub repository at Java 8 Lambda Source Code
Java 8 Lambda Expressions Syntax
Java Lambda Expression Syntax
(argument-list) -> {body}
Java lambda expression consists of three components.
- Argument-list: It can be empty or non-empty as well.
- Arrow-token: It is used to link arguments-list and body of expression.
- Body: It contains expressions and statements for the lambda expression.
Useful Java Lambda Expressions Examples
1. Java Simple Lambda Expression Example
Here, we are implementing a Drawable functional interface method using the lambda expression:
interface Drawable{
public void draw();
}
public class LambdaExpressionExample {
public static void main(String[] args) {
int width=10;
//with lambda
Drawable withLambda=()->{
System.out.println("Drawing "+width);
};
withLambda.draw();
}
}
Output :
Drawing 102. Java Lambda Expression Example: No Parameter
Please refer to the comments in the code, which indicates that code with Lambda expression and without Lambda expression.
interface Sayable {
public String say();
}
public class JLEExampleNoParameter {
public static void main(String[] args) {
// without lambda expression
Sayable sayable = new Sayable() {
@Override
public String say() {
return "Return something ..";
}
};
sayable.say();
// with lambda expression
Sayable withLambda = () -> {
return "Return something ..";
};
withLambda.say();
}
}
3. Java Lambda Expression Example: Single Parameter
Please refer to the comments in the code, which indicates that code with Lambda expression and without Lambda expression.
interface Printable {
void print(String msg);
}
public class JLEExampleSingleParameter {
public static void main(String[] args) {
// without lambda expression
Printable printable = new Printable() {
@Override
public void print(String msg) {
System.out.println(msg);
}
};
printable.print(" Print message to console....");
// with lambda expression
Printable withLambda = (msg) -> System.out.println(msg);
withLambda.print(" Print message to console....");
}
}
Output :
Print message to console....
Print message to console....4. Java Lambda Expression Example: Multiple Parameters
Please refer to the comments in the code, which indicates that code with Lambda expression and without Lambda expression.
interface Addable{
int add(int a,int b);
}
public class JLEExampleMultipleParameters {
public static void main(String[] args) {
// without lambda expression
Addable addable = new Addable() {
@Override
public int add(int a, int b) {
return a + b;
}
};
addable.add(10, 20);
// with lambda expression
// Multiple parameters in lambda expression
Addable withLambda = (a,b)->(a+b);
System.out.println(withLambda.add(10,20));
// Multiple parameters with data type in lambda expression
Addable withLambdaD = (int a,int b) -> (a+b);
System.out.println(withLambdaD.add(100,200));
}
}
5. Java Lambda Expression Example: Multiple Statements
Let's see how to write multiple statements in Lambda expressions:
interface IAvarage{
double avg(int[] array);
}
public class JLEExampleMultipleStatements {
public static void main(String[] args) {
// without lambda expression, IAvarage implementation using anonymous class
IAvarage avarage = new IAvarage() {
@Override
public double avg(int[] array) {
double sum = 0;
int arraySize = array.length;
System.out.println("arraySize : " + arraySize);
for (int i = 0; i < array.length; i++) {
sum = sum + array[i];
}
System.out.println("sum : " + sum);
return (sum/ arraySize);
}
};
int[] array = {1,4,6,8,9};
System.out.println(avarage.avg(array));
// with a lambda expression
// You can pass multiple statements in lambda expression
IAvarage withLambda = (withLambdaArray) -> {
double sum = 0;
int arraySize = withLambdaArray.length;
System.out.println("arraySize : " + arraySize);
for (int i = 0; i < withLambdaArray.length; i++) {
sum = sum + withLambdaArray[i];
}
System.out.println("sum : " + sum);
return (sum/ arraySize);
};
int[] withLambdaArray = {1,4,6,8,9};
System.out.println(withLambda.avg(withLambdaArray));
}
}
6. Java Lambda Expression Example: Creating Thread
Let's write the example to use a lambda expression to implement Runnable interface:
public class JLEExampleRunnable { public static void main(String[] args) { //without lambda, Runnable implementation using anonymous class Runnable runnable = new Runnable() { @Override public void run() { System.out.println(" Runnable example without lambda exp."); } }; Thread thread = new Thread(runnable); thread.start(); //with lambda Runnable withLambda = () -> System.out.println(" Runnable example with lambda exp."); Thread thread1 = new Thread(withLambda); thread1.start(); } }
Output :
Runnable example without lambda exp.
Runnable example with lambda exp.
7. Java Lambda Expression Example: Comparator
Let's write an example to demonstrate how to use a lambda expression to implement Comparator interface:
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class JLEComparatorExample {
public static void main(String[] args) {
List<Person> listOfPerson = new ArrayList<Person>();
listOfPerson.add(new Person("abc", 27));
listOfPerson.add(new Person("mno", 26));
listOfPerson.add(new Person("pqr", 28));
listOfPerson.add(new Person("xyz", 27));
// Without lambda expression.
// Sort list by age
Comparator<Person> comparator = new Comparator<Person>() {
@Override
public int compare(Person o1, Person o2) {
return o1.getAge() - o2.getAge();
}
};
Collections.sort(listOfPerson, comparator);
System.out.println(" sort persons by age in ascending order");
for (Person person : listOfPerson) {
System.out.println(" Person name : " + person.getName());
}
// With lambda expression.
// Sort list by age
Collections.sort(listOfPerson, (Person o1, Person o2) -> {
return o1.getAge() - o2.getAge();
});
// Use forEach method added in java 8
System.out.println(" sort persons by age in ascending order");
listOfPerson.forEach(
(person) -> System.out.println(" Person name : " + person.getName()));
}
}
class Person {
private String name;
private int age;
public Person(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
8. Java Lambda Expression Example: Event Listener
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
public class LambdaEventListenerExample {
public static void main(String[] args) {
JTextField tf=new JTextField();
tf.setBounds(50, 50,150,20);
JButton b=new JButton("click");
b.setBounds(80,100,70,30);
// lambda expression implementing here.
b.addActionListener(e-> {tf.setText("hello swing");});
JFrame f=new JFrame();
f.add(tf);f.add(b);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setLayout(null);
f.setSize(300, 200);
f.setVisible(true);
}
}
9. Iterate ArrayList with forEach() method + Lambda Expression Example
package net.javaguides.collections; import java.util.Arrays; import java.util.Iterator; import java.util.List; /** * * Java program to demonstrate different ways to Iterate over an ArrayList in Java * @author Ramesh Fadatare * */ public class DifferentWaysListIterateProgram { public static void main(String...args) { List < String > courses = Arrays.asList("C", "C++", "Core Java", "J2EE", "Spring", "Hibernate", "Python"); // JDK 8 streaming example lambda expression courses.stream().forEach(course -> printCourse(course)); // JDK 8 streaming example method reference courses.stream().forEach(DifferentWaysListIterateProgram::printCourse); // JDK 8 for each with lambda courses.forEach(course -> printCourse(course)); // JDK 8 for each courses.forEach(DifferentWaysListIterateProgram::printCourse); } // common method to print course private static void printCourse(String course) { System.out.println("course name :: " + course); } }
10. Iterate HashSet with forEach() method + Lambda Expression Example
package net.javaguides.collections; import java.util.HashSet; import java.util.Iterator; import java.util.Set; /** * Java program to demonstrate different ways to iterate over a Set in Java * * @author Ramesh Fadatare * */ public class DifferentWaysSetIterateProgram { public static void main(String...args) { Set < String > courses = new HashSet < String > (); courses.add("Java"); courses.add("C"); courses.add("C++"); courses.add("Python"); courses.add("Scala"); // JDK 8 streaming example lambda expression courses.stream().forEach(course -> coursePrinter(course)); // JDK 8 streaming example method reference courses.stream().forEach(DifferentWaysSetIterateProgram::coursePrinter); // JDK 8 for each with lambda courses.forEach(course -> coursePrinter(course)); // JDK 8 for each courses.forEach(DifferentWaysSetIterateProgram::coursePrinter); } // common method to print course private static void coursePrinter(String course) { System.out.println("course name :: " + course); } }
11. Iterate HashMap with forEach() method + Lambda Expression Example
package net.javaguides.collections; import java.util.HashMap; import java.util.Iterator; import java.util.Map; /** * This program demonstrate different ways to iterate over a Map in Java * * @author Ramesh Fadatare * */ public class DifferentWaysMapIterateProgram { public static void main(String...args) { Map < Integer, String > coursesMap = new HashMap < Integer, String > (); coursesMap.put(1, "C"); coursesMap.put(2, "C++"); coursesMap.put(3, "Java"); coursesMap.put(4, "J2EE"); coursesMap.put(5, "Python"); coursesMap.put(6, "Scala"); // JDK 8 for each with lambda coursesMap.forEach((k, v) -> coursePrinter(k, v)); // JDK 8 for each method reference coursesMap.forEach(DifferentWaysMapIterateProgram::coursePrinter); } // common method to print map key value private static void coursePrinter(Integer number, String brand) { System.out.println("course no : " + number + " and course name : " + brand); } }
Excelent post, but there is an issue in the example on point 6. "Java Lambda Expression Example: Creating Thread"
ReplyDelete//with lambda
Runnable withLambda = () -> System.out.println(" Runnable example with lambda exp.");
Thread thread1 = new Thread(runnable);
thread1.start();
Replace witth:
//with lambda
Runnable withLambda = () -> System.out.println(" Runnable example with lambda exp.");
Thread thread1 = new Thread(withLambda);
thread1.start();
Yes fixed it. Thanks for reporting.
Delete