JAVA Lambda Expressions

Introduction:

• Java's first step into functional programming
• It is an anonymous function and doesn't belong to any class
• It implements the interface methods in a concise expression clearly.
• It provides the implementation of functional interface and simplifies the software development
• First programming language uses Lambda expression is LISP, later on C, C++, C#, .Net, RUBY and etc.

Syntax:

parameter -> expression body

→ Arrow operator is introduced in Java through lambda expression that divides it into two parts(Parameter & Body).

Characteristics:

→ Optional Type Declarations

→ Optional parenthesis around parameters and curly braces

→ Optional return keyword

Interview Questions:

1. Objective of Lambda expression in JAVA:

• To enable the functional programming benefits
• To write the code in more readable, maintainable and concise code
• To use API's very easily and effectively
• To enable parallel processing

2. Difference between Anonymous Inner class and Lambda Expression.

Anonymous Inner class	Lambda Expression
class without name	function without name
can extends abstract, concrete classes and interface	can extends only the functional interface (Single Abstract Method)
can declare instance variable	can’t declare instance variable
can be instantiated	can’t be instantiated
Inside anonymous inner class, this always refers current anonymous inner class object but not outer class object	Inside lambda expression, this always refers Outer class object
highly recommended for multiple method handling	highly recommended for one abstract method in an interface i.e, functional interface
separate .class file generated for every anonymous class	no separate .class file generated during compilation
object memory allocated in heap area	reside in permanent memory of JVM (method area)