Java 8

Java8 – Optional

Optional is a container object used to contain not-null objects. Optional object is used to represent null with absent value. This class has various utility methods to facilitate code to handle values as ‘available’ or ‘not available’ instead of checking null values. It is introduced in Java 8 and is similar to what Optional is in Guava.

Class Declaration

Following is the declaration for java.util.Optional<T> class −

public final class Optional<T> extends Object

Class Method

Sr.No.Method & Description
1static <T> Optional<T> empty() – Returns an empty Optional instance.
2boolean equals(Object obj) – Indicates whether some other object is “equal to” this Optional.
3Optional<T> filter(Predicate<? super <T> predicate) – If a value is present and the value matches a given predicate, it returns an Optional describing the value, otherwise returns an empty Optional.
4<U> Optional<U> flatMap(Function<? super T,Optional<U>> mapper) – If a value is present, it applies the provided Optional-bearing mapping function to it, returns that result, otherwise returns an empty Optional.
5T get() – If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.
6int hashCode() – Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
7void ifPresent(Consumer<? super T> consumer) – If a value is present, it invokes the specified consumer with the value, otherwise does nothing.
8boolean isPresent() – Returns true if there is a value present, otherwise false.
9<U>Optional<U> map(Function<? super T,? extends U> mapper) – If a value is present, applies the provided mapping function to it, and if the result is non-null, returns an Optional describing the result.
10static <T> Optional<T> of(T value) – Returns an Optional with the specified present non-null value.
11static <T> Optional<T> ofNullable(T value) – Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
12T orElse(T other) – Returns the value if present, otherwise returns other.
13T orElseGet(Supplier<? extends T> other) – Returns the value if present, otherwise invokes other and returns the result of that invocation.
14<X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) – Returns the contained value, if present, otherwise throws an exception to be created by the provided supplier.
15String toString() – Returns a non-empty string representation of this Optional suitable for debugging.

This class inherits methods from the following class −

  • java.lang.Object

Optional Example

Create the following Java program using any editor of your choice in, say, C:\hitechpoints\workspace\java8\src>.

Java8Optional.java
import java.util.Optional;

public class Java8Optional {
	
	public static void main(String args[]) {
		  Java8Optional java8Optional = new Java8Optional();
	      Integer value1 = new Integer(20);
	      Integer value2 = null;
			
	      // 1. Optional.of - throws NullPointerException if passed parameter is null
	      Optional<Integer> a = Optional.of(value1);
	      
	      // 2. Optional.ofNullable - allows passed parameter to be null.
	      Optional<Integer> b = Optional.ofNullable(value2);
	      System.out.println(java8Optional.add(a,b));
	   }
		
	   public Integer add(Optional<Integer> a, Optional<Integer> b) {
	      // 1. Optional.isPresent - checks the value is present or not		
	      System.out.println("First parameter is present: " + a.isPresent());
	      System.out.println("Second parameter is present: " + b.isPresent());
			
	      // 2. Optional.get - gets the value, value should be present
	      Integer value2 = a.get();
	      
	      // 3. Optional.orElse - returns the value if present otherwise returns
	      // the default value passed.
	      Integer value1 = b.orElse(new Integer(0));
	      
	      return value1 + value2;
	   }

}

Output:

Compile the class using javac compiler as follows −

C:\hitechpoints\workspace\java8\src>javac Java8Optional.java

Now run the Java8Optional as follows −

C:\hitechpoints\workspace\java8\src>java Java8Optional

It should produce the following output −

First parameter is present: true
Second parameter is present: false
20

About the Author: Elavarasan PK

Technical Specialist, Intersoft Data Labs