Functional Programming

Question 1

What is supplier?

Answer 1

Supplier is a functional interface that is used where we want to generate or supply values without taking any input

Question 2

What is the method used to get the valuse from Supplier

Answer 2

get();

Eg.., Supplier date = LocalDate::now;
Localdate date = date.get();

Question 3

When does a supplier often used?

Answer 3

A supplier is often used to when constructing a new objects.

Question 4

How do you create a string builder objects using supplier

Answer 4

Supplier stringBuilder = StringBuilder::new;
or
Supplier stringBuilder = () -> new StringBuilder();

Question 5

Can you create a Supplier of ArrayList type?

Answer 5

Supplier> supplier = ArrayList::new;

Question 6

Consumer?

Answer 6

Consumers are used when we want to pass something but doesnt get anything in return.

Question 7

BiConsumer?

Answer 7

That accepts two inputs but doesn’t return anything.

It two inputs doesn’t necessary to be same.

Question 8

When is a predicate often used?

Answer 8

Predicates are used for filtering/matching purposes

Question 9

What is a BiPredicate?

Answer 9

BiPredicate is same as Predicate except that it take two parameters instead of one

Question 10

definition of Predicate and BiPredicate?

Answer 10

@FunctionalInterface
	public interface Predicate{
		boolean test(T t);
	}

	@FunctionalInterface
	public interface BiPredicate{
		boolean test(T t, U u);
	}

Question 11

what is the implications of the below statements?

BiPredicate bp1= String::startsWith;
BiPredicate bp2 = (String s1, String s2) -> s1.startsWith(s2);

Answer 11

1. startsWith() is an instance method.

2. Which means the first parameter in Bipredicate here is a instance variable on which the method is called

Question 12

What method does the Predicate provides for && and ! respectively? What kind of method it is?

Answer 12

&& -> and();
! -> negate();
They are default methods of Predicates

Question 13

What is a function?

Answer 13

A function takes a parameter of any type and returns a value of different type.

A Bifunction takes two parameter of any type and returning a value of any type.

The types doesnt need to be different

Question 14

What is the method used for Function?

Answer 14

apply(T t) for Function

apply(T t, U u) for Bifunction

Question 15

What is the UNARYoPERATOR AND bINARYoPERATOR?

Answer 15

they are same as Functions except that they need the parameters of same type and return types also same type

Question 16

What is the UNARYoPERATOR AND bINARYoPERATOR?

Answer 16

they are same as

Question 17

How to clear in deciding whether to pick predicate or function?

Answer 17

When you see a boolean returned, think Predicate unless the generics specify a Boolean return type.

Remeber, Predicate returns boolean return type, not Boolean object

Question 18

What is a difference b/w Function and UnaryOperator apart fromtypes?

Answer 18

Function should specify two generics and UnaryOperator should specify One generics.

BiFunction specify three generics and BinaryOperator specify one generics

Question 19

What is a difference b/w Function and UnaryOperator apart fromtypes?

Answer 19

Function should specify two generics and UnaryOp

Question 20

Method to check whether an Optional is having value or not.

Answer 20

Optional.isPresent()

Question 21

Method to check whether an Optional is having value or not.

Answer 21

Optional.isEmpty()

Question 22

What is the exception we get when there is no value in Optional and we try to get it?

Answer 22

NoSuchElementException

Question 23

A method that wraps the value if Optional contains value or returns empty when optional is null?

Answer 23

Optional.ofNullable(value)

Question 24

important Optional instance mthod to remember

Answer 24

get(), isPresent(), ifPresent(Consumer c), orElse(T t),orElseGet(Suppliers), oeElseThrow(Supplier s)