Java 8 Predicate, Function, Chaining, Predicate Joining interview questions (Live Demo) Code Decode

In this video of code decode we have covered Java 8 || Predicate || Function || Chaining || Predicate Joining interview questions (Live Demo)

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here are lots of new features which were added in Java 8. Here is the list of important features which are mostly asked as java 8 interview questions:

Lambda Expression
Stream API
Default methods in the interface
Predicate
Functional Interface
Optional
Method references
Date API
Nashorn, JavaScript Engine

Main advantages of using Java 8?
More compact code
Less boiler plate code
More readable and reusable code
More testable code
Parallel operations

Q) What are predicates?
Predicate is a predefined Functional Interface (Having only 1 abstract method).
The only abstract method of predicate is test(T t):
public boolean test(T t);
Whenever we want to check some boolean condition then you can go for Predicates.

Q) How to use Predicates?
Say if you need to test if the length of the given string is greater than or equal to 5. Then in such situations where you need to test conditions, use test() method of predicate.

Q) Type parameter and return types of Predicates?
Input to predicate can be anything like
Hence only 1 type argument is required which is input type in predicate.
Return type is not required as its always Boolean only.

Q) Advantages of Predicates?
Code Reusability

If you have same conditions being used 100 times in a prgram then you can write once and just use 100 times with checkLength.test(different string to be tested).

Conditional checks are holded by Functional interfaces.

Q) What is Predicate joining?
You can combine predicates in serial predicate

Three ways to join :
And
Or
Negate

Eg if you want to test 2 conditions:
To check length of string
To check if length is even.

Q) What are Functions
Function is also a predefined Functional Interface (Having only 1 abstract method).

The only abstract method of Function is apply(T t);

R apply(T t);

Given some input perform some operation on input and then produce / return result (not necessary a boolean value).

This takes 1 input and returns one output.
In predicate we used to take 1 input and return type is always boolean.
In function return type is not fixed hence we declare both input type and return type.

Q) What is Functional chaining

We can combine / chain multiple functions together with andThen .

There are two ways to combine functions:
f1.andThen(f2).apply(Input); - first f1 then f2
f1.compose(f2).apply(Input) - first f2 then f1


Multiple functions can be chained together like :
f1.andThen(f2).andThen(f3).andThen(f4).apply(Inputs);

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