Core java interview Questions You'll Most Likely Be Asked (Second Edition)

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208.
CHAPTER
02
Lambda Expressions
What is a lambda expression? What are the benefits of
using lambda expressions?
Answer:
A lambda expression is used to specify a function without a
name. It is used to implement the abstract method within a
functional interface. Lambda expressions have several benefits
as follows:
They make code concise. Prior to Java 8, developers had to
write a lot of code to implement an interface which made the
code lengthy and verbose. Lambda expressions get rid of
most of the boilerplate code associated with implementing an
interface.
They allow passing around code as method arguments.
They allow providing different implementation for the same
method on the fly.
Some of the other new features added by Java 8 like for–each
and Streams also use lambda expressions.
How are lambda expressions and functional interfaces
related to each other?
Answer:
A functional interface is an interface with a single abstract
method. A lambda expression is used to implement the abstract
method specified in the functional interface.

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Functional interfaces were added by Java 8 to support lambda
expressions and add functional programming support to Java.
Since Java is an object–oriented language, lambda expressions
cannot be written on their own. They need to be associated with
an object. So, Java 8 introduced functional interfaces and made it
compulsory for lambda expressions to be used only with
functional interfaces. By making a lambda expression implement
a functional interface method, the lambda expression becomes
an implementation of the functional interface. Functional
interfaces and lambda expressions together help to write clean
and concise Java code.