Lambda Expressions Java 8 Features usage

Content
• Understanding Lambdas
• Using Lambdas
• Functional Interface
• Method references
• Collections improvements

Why Lambdas?
• Enables Functional Programming
• Readable and concise code
• Enables us to write better APIs and libraries which are easier to use
• Support for parallel processing

Functional Programming VS OOP
• Functional programming allow you to write more readable and
maintainable code.(in some cases)
• Problems in OOP
• Everything is object - all code blocks are "associated" with class and objects ,
which is a problem some time
• We cannot have a independent functions , it have to be a part of function.
• Also allow us to use functions as values.

Function as a value
aBlockOfCode = public void () {
System.out.println("Hello World");
}
perfom
->
aBlockOfCode = () -> {
}
aBlockOfCode = () -> System.out.println("Hello World");

Type Inference
• Your lambda Expression infer type of function and its return type
from the interface(functional interface).
public static void main(String[] args)
{
//StringLengthLambda myStringLenthLambda = (String s) -> s.length();
//StringLengthLambda myStringLenthLambda = (s) -> s.length();
StringLengthLambda myStringLenthLambda = s -> s.length();
System.out.println("String Length :: " + myStringLenthLambda.getLength("Hello World!!"));
}
interface StringLengthLambda
{
int getLength(String s);
}

Lambda Vs Interface Implementation
• We can implement the functional interface in two ways.
• By Implementing the lambda Expression
• By Creating the Anonymous class implementation
Greeting innerClassGreeting = new Greeting() {
@Override
public void perfom() {
}
};
innerClassGreeting.perfom();
Greeting myLambdaFunction = () -> System.out.println("Hello World");
myLambdaFunction.perfom();

Lambda Vs Interface Implementation
• For the most purposes you can think of the lambda expression as the
shortcut for creating these kind of anonymous inner classes but its
not exactly true.
• There are things that inner class does which is different from what
these lambda expressions do.
• In case of lambda expression its not exactly creating an anonymous
class, will look at those differences in a further slides.

Runnable Using Lambdas
• You can use lambda in order to create Runnable.
• Implement Using anonymous inner class
• Implement Using Lambda Expression
public static void main(String[] args) {
Thread myThread = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Printed inside runnable");
}
});
myThread.start();
}
Thread myLambdaThread = new Thread(() -> System.out.println("Printed inside Lambda Runnable"));
myLambdaThread.start();

Functional Interface
• Any interface with a SAM(Single Abstract Method) is a functional
interface
• Interface can have multiple default methods but it should have only
one abstract method(Java 8)
• its implementation may be treated as lambda expressions.
• It's recommended that all functional interfaces have an informative
@FunctionalInterface annotation.
• Add @FunctionalInterface on Greeting

Implementation Of Lambda Expression
• Lets do some hands on exercise to understand advantages of lambda
expression with collections.

Predicate Interface
• Represents a predicate (boolean-valued function) of one argument.
• This is a functional interface whose functional method is test(Object).

Consumer Interface
• Represents an operation that accepts a single input argument and
returns no result.
• This is a functional interface whose functional method is
accept(Object).

Exception Handling in lambda Expression
• Create a lambda expression which X in an array of integers and a key
which is and do the mathematical operation for each element in array
given a key.

Closers in Lambda Expressions
• Understand what is effectively final.
• Understand the freeze value in lambda expression

Difference between lambda and Anonymous
Inner Class.
• In an anonymous inner class when using the this reference , it
overwrite the this reference to the anonymous inner class instance.
• In the case of a lambda that does not happen. It still refers to the
instance that it points to the outside of the lambda(no overriding of
this reference that happens).
• Lets have an example in eclipse.

Streams
• A sequence of elements supporting sequential and parallel aggregate
operations.
• Stream Operations
• Intermediate Operations (Return Stream Object)
• Map
• Filter
• Sorted
• Terminal Operations
• Collect
• forEach
• Reduce
• Stream Operations don’t change the source.

Optional
• The purpose of the class is to provide a type-level solution for
representing optional values instead of null references
• Static methods of Optional class
• empty()
• of()
• isPresent()

Date Time API
• Java 8 introduces a new date-time API under the package
java.time. Following are some of the important classes
introduced in java.time package.
• Instant
• LocalDate
• LocalTime
• LocateDateTime

Lambda Expressions Java 8 Features usage

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