Java 8 Optional Class with examples

          In java8 introduced new class called Optional, using optional we can handle NullPointerException without using any null check condition.( Refer - Java 8 features) It provided many methods and using those it will be helpful to write cleanable code.

         Using optional if variable value is null then using orElse method we can have a null functionality code inside it.

 Below are the methods available in Optional class,

The Optional.ofNullable() --- > method returns a Non-empty Optional if a value present in the given object. Otherwise returns an empty Optional. 

Optional.empty() -- > method is useful to create an empty Optional object.

Optional.of(value) --> creates an Optional object using value. 

Optional.ifPresent -- > If optional variable value is present, invoke the specified consumer with the value, otherwise, do nothing.

orElse --> If optional variable value is null then invokes orElse method.

 orElseGet --> If optional variable value is null then invokes orElse method and return the result of that invocation.

 orElseThrow --> If optional variable value is null then invokes orElseThrow method and throws the exception provided in the method.

 get -- > method returns the value from the optional.

 isPresent - if optional variable value is present/exist then return true else it's false.

Optional Class Code Example - 

import java.util.Optional;

public class OptionalClassUsages {
	
	public static void main(String[] args) {
		
		//ofNullable, orElse, orElseGet and orElseThrow method example
		String str = "Optional with ofNullable method usage";
		System.out.println(Optional.ofNullable(str).orElse("null logic"));
		
		str = null;
		System.out.println(Optional.ofNullable(str).orElse("null logic"));
		System.out.println(Optional.ofNullable(str).orElseGet(() -> "orElseGet method"));
		
		try {
			Optional.ofNullable(str).orElseThrow(() -> {
				return new Exception("orElseThrow Exception");
			});
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		//optional of, ifPresent, filter usages
		Optional<String> optional = Optional.of("ab");
		optional.ifPresent(s-> System.out.println(s));
		optional.filter(s->s.equals("ab"))
				.ifPresent(s-> System.out.println("ifPresent method usage"));
		
		//isPresent and get method usage example
		System.out.println(optional.isPresent());
		System.out.println(optional.get());	
	}
}

Output:- 

Optional with ofNullable method usage
null logic
orElseGet method
java.lang.Exception: orElseThrow Exception
	at com.main.OptionalClassUsages.lambda$1(OptionalClassUsages.java:19)
	at java.util.Optional.orElseThrow(Optional.java:290)
	at com.main.OptionalClassUsages.main(OptionalClassUsages.java:18)
ab
ifPresent method usage
true
ab

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Reference posts:

1) Java 8 features

2) String related interview questions and answers

3) Java 8 forEach method examples

4) Java 8 - Consumer Interface with examples