Java Lambda Expression – Complete Guide
In Java SE 8, Lambda expression was added as a new and important feature. An expression can be used to represent a single-method interface clearly and concisely. In a collection library, it is extremely useful as it assists in iterating, filtering, and extracting data from the collection.
A functional interface can be achieved by implementing an interface using the Lambda expression. It saves a lot of code. In cases of lambda expressions, we don’t need to define the method again to provide the implementation.
Functional Interface:
Lambda expression provides an implementation of functional interfaces. An interface that has only one abstract method is called a functional interface. Java provides an annotation @FunctionalInterface, which is used to declare an interface as a functional interface.
Use of Lambda Expression:
- To create a functional interface that is implemented.
- By writing very little coding.
Lambda Expression Syntax:
(argument_list) -> {body}
Three components make up Java lambda expressions.
- Argument_list: It has the option of either being empty or non-empty.
- Arrow token: It is used to link the arguments list and body of expression.
- Body: It contains statements and expressions for lambda expressions.
1 No Parameter Syntax:
() -> {
//Body of lambda expression
}
- One Parameter Syntax:
( b1 ) -> {
//Body of lambda expression
}
3 Two Parameter Syntax:
( b1, b2 ) -> {
//Body of lambda expression
}
Comparison with and without Lambda Expression :
Without Lambda Expression :
Ex:
interface Student{
public void info();
}
public class LambdaExpressionDemo {
public static void main(String[] args) {
int rollNo=10;
String name = “Nitin”;
//without lambda, Student implementation using anonymous class
Student d=new Student(){
public void info(){
System.out.println(“Student Information “+ rollNo + ” ” + name);
}
};
d.info();
}
}
With Lambda Expression :
Ex:
interface Student{
public void info();
}
public class LambdaExpressionDemo {
public static void main(String[] args) {
int rollNo=10;
String name = “Nitin”;
//without lambda, Student implementation using anonymous class
Student d = () -> {
System.out.println(“Student Information “+ rollNo + ” ” + name);
};
d.info();
}
}
Java Lambda Expression Example With No Parameter :
Ex:
interface SayHello{
public String welcome();
}
public class LambdaExpressionNoParameterDemo {
public static void main(String[] args) {
//Lambda expression with no parameter
SayHello s1 = () -> {
return “Welcome to IEC, Pune”;
};
System.out.println(s1.welcome);
}
}
Java Lambda Expression Example With One Parameter :
Ex:
interface SayHello{
public String welcome(String msg);
}
public class LambdaExpressionNoParameterDemo {
public static void main(String[] args) {
//Lambda expression with no parameter
SayHello s1 = (msg) -> {
return “Welcome to ” + msg;
};
System.out.println(s1.welcome(“IEC, Pune”));
}
}
Java Lambda Expression Example With Multiple Parameters:
Ex:
interface SayHello{
public String welcome(String msg1, String msg2);
}
public class LambdaExpressionNoParameterDemo {
public static void main(String[] args) {
//Lambda expression with no parameter
SayHello s1 = (msg1, msg2) -> {
return “Welcome to ” + msg1 + “ and we are providing ” + msg2;
};
System.out.println(s1.welcome(“IEC, Pune”, “IT courses.”));
}
}
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Author: Ambarish Durani
JAVA Trainer
IT Education Centre Placement & Training Institute
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