Lambda Expression For anyone that needs Java Lambda notes

Lambda Expression
Dr.M.S.Bhuvaneswari, SCORE,VIT

Lambda Expression
• It is an anonymous (that is, unnamed) method
• A lambda expression results in a form of anonymous class.
• This method is not executed on its own. Instead, it is used to implement a
method defined by a functional interface.
• Lambda expressions are also commonly referred to as closures

Lambda Expression Fundamentals
• The lambda expression introduces a new syntax element and operator into the
Java language
• lambda operator or the arrow operator
• Lambda operator divides the lambda expression into two parts.
• The left side specifies any parameters required by the lambda expression.
• On the right side is the lambda body, which specifies the actions of the lambda
expression
• Syntax:
(param1,param2) -> body

• lambda expression consist 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 lambda expression.

Lambda Expression
• No Parameter Syntax
() -> {
//Body of no parameter lambda
}
• One Parameter Syntax
(param1) -> {
}

Lambda Expression
Multiple parameter Syntax
(param1, param2) -> {
}

Functional Interface
• A functional interface is an interface that contains one and only one abstract method.
Example: Runnable is a functional interface because it defines only one method
run( )
• It typically represents a single action.
• A functional interface defines the target type of a lambda expression.
• When a lambda expression occurs in a target type context, an instance of a class is
automatically created that implements the functional interface, with the lambda
expression defining the behavior of the abstract method declared by the functional
interface
• A functional interface is sometimes referred to as a SAM type, where SAM stands for
Single Abstract Method.

• Java defines two types of lambda bodies.
▪ single expression
▪ block of code
Normal Method
=============
int findSum()
{
return 20;
}
Lambda Expression
================
() -> 20

Lambda Expression
• In order for a lambda expression to be used in a target type context, the type of
the abstract method and the type of the lambda expression must be compatible
• Rules
▪ The type and number of the lambda expression’s parameters must be
compatible with the method’s parameters;
▪ The return types must be compatible; and
▪ Any exceptions thrown by the lambda expression must be acceptable to the
method

Lambda Expression Example1
interface FuncIntf {
public int getValue();
}
class ClsIntf implements FuncIntf
{
public int getValue()
{
return 20;
}
}
class MyClass
{
public static void main(String[] args)
{
FuncIntf intfRef = new ClsInft();
System.out.println("Value is:"+intfRef.getValue());
}
}

int getValue();
}
class MyClass
{
{
FuncIntf intfRef = new ClsInft();
}
}

int getValue();
}
class MyClass
{
{
FuncIntf intfRef = ;
}
}

int getValue();
}
class MyClass
{
{
FuncIntf intfRef = () -> 20;
}
}
Lambda Expression () -> 20
================
• Implements the method getValue() in FuncIntf
• Returns an instance of the class

Lambda Expression with parameters - Example2
interface FuncIntf
{
int findSum(int a,int b);
}
class MyClass
{
{
FuncIntf intfRef = (x,y)-> {int c=x+y;return c;};
System.out.println("Value is:"+intfRef.findSum(6,8));
}
}

Lambda Expression with parameters type- Example3
interface FuncIntf
{
}
class MyClass
{
{
FuncIntf intfRef = (int x, int y)-> {int c=x+y;return c;};
}
}

Lambda Expression with parameters type- Example4
interface FuncIntf
{
}
class MyClass
{
{
FuncIntf intfRef = (int x, int y)-> {int c=x+y;return c;}; //with return(with multiple statements)
FuncIntf intfRef1 = (int x,int y)-> (x+y); //without return(with only one statement)
System.out.println("Value is:"+intfRef1.findSum(6,8));
}
}

Thread Implementation without Lambda
class MyThread implements Runnable{
public void run()
{
try {
for(int i = 5; i > 0; i--) {
System.out.println("Child Thread: " + i);
Thread.sleep(500);
}
}
catch (InterruptedException e) {
System.out.println("Child interrupted.");
}
System.out.println("Exiting child thread.");
}
}

Thread Implementation without Lambda
Runnable rintf=new MyThread()
Thread th1=new Thread(rintf)
th1.start()

Thread Implementation using Lambda
Thread th1=new Thread(() -> {
try {
for(int i = 5; i > 0; i--) {
System.out.println("Child Thread: " + i);
Thread.sleep(500);
}
}
catch (InterruptedException e) {
System.out.println("Child interrupted.");
}
System.out.println("Exiting child thread.");
});
th1.start();

References
• https://www.javatpoint.com/java-lambda-expressions

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