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This Edureka tutorial on “Lambda Expressions in Java” will introduce you to a new Java feature called Lambda Expressions. It will also talk about the functional interface in Java. Through this tutorial you will learn the following topics:
Java Lambda Expressions
Functional Interface
Lambda Parameters
Lambda as an Object
Lambda Value Capture
Method References as lambdas
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It provides the implementation of a functional interface & simplifies the software development
It provides a clear and concise way to represent a method interface via an expression
Java Lambda Expressions
It is an anonymous function that doesn’t have a name and doesn’t belong to any class
Java lambda expressions are Java's first step into functional programming
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parameter -> expression body->
Java Lambda Expressions
Syntax
Characteristics
-> Optional Type Declarations
-> Optional Parenthesis Around Parameters
-> Optional Curly Braces
-> Optional return keyword
Arrow Operator is introduced in Java through lambda
expressions that divides it into two parts i.e Parameters & Body
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Functional Interface
Functional Interface is
an interface that
contains exactly one
abstract method
It can have any
number of default or
static methods along
with object class
methods
Java provides
predefined functional
interfaces to deal with
functional
programming
Runnable,
ActionListener,
Comparable are some
of the examples of
functional interfaces
01 02 03 04
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Functional Interface
@FunctionalInterface
interface displayable{
void display(String msg);
}
public class Test implements displayable{
public void display(String msg){
System.out.println(msg);
}
public static void main(String[] args) {
Test dis = new Test();
dis.display("Welcome to Lambda Tutorial by Edureka!");
}
}
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Lambda Parameters
Lambda Expressions can take parameters just like methods
1 2 3
Zero Parameters One Parameter Multiple Parameters
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Lambda Parameters
1
2
3
Zero Parameters
One Parameter
Multiple Parameters
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Lambda Parameters
1
2
3
Zero Parameters
One Parameter
Multiple Parameters
() -> System.out.println("Zero parameter lambda");
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Lambda Parameters
1
2
3
Zero Parameters
One Parameter
Multiple Parameters
() -> System.out.println("Zero parameter lambda");
(param) -> System.out.println("One parameter: " + param);
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Lambda as an Object
A Java lambda expression is essentially an object that can be assigned to a variable and passed around
public interface LambdaComparator {
public boolean compare(int a1, int a2);
}
LambdaComparator myComparator = (a1, a2) -> return a1 > a2;
boolean result = myComparator.compare(2, 5);
Interface
Implementing
class
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Variable Capture
Java lambda expression can access variables that are declared outside the lambda function body under
certain circumstances
1 2 3
Local Variable Instance Variables Static Variables
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Lambda Parameters
1
2
3
Local Variable
Instance Variables
Static Variables
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Lambda Parameters
1
2
3
Local Variable
String myStr = "Welcome to Edureka!";
MyLambda dis = (chars) -> {
return myStr + ":" + new String(chars);
};
Instance Variables
Static Variables
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Lambda Parameters
1
2
3
Local Variable
Instance Variables
Static Variables
public class LambdaStaticConsumerDemo {
private String str = "Lambda Consumer";
public void attach(LambdaStaticProducerDemo eventProd){
eventProd.listen(e -> {
System.out.println(this.str);
});
}
}
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Lambda Parameters
1
2
3
Local Variable
Instance Variables
Static Variables
public class LambdaStaticConsumerDemo {
private static String myStaticVar = "Edureka!";
public void attach(LambdaStaticProducerDemo eventProd){
eventProd.listen(e -> {
System.out.println(myStaticVar);
});
}
}
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Method References
Java lambda expression can access variables that are declared outside the lambda function body under
certain circumstances
Static Method
Reference
1 2 3 4
Parameter Method
Reference
Instance Method
Reference
Constructor Method
Reference