Guava - Optional Class

Class Declaration

Following is the declaration for com.google.common.base.Optional<T> class −

@GwtCompatible(serializable = true)
public abstract class Optional<T>
   extends Object
      implements Serializable

Class Methods

Sr.No	Method & Description
1	static <T> Optional<T> absent() Returns an Optional instance with no contained reference.
2	abstract Set<T> asSet() Returns an immutable singleton Set whose only element is the contained instance if it is present; an empty immutable Set otherwise.
3	abstract boolean equals(Object object) Returns true if object is an Optional instance, and either the contained references are equal to each other or both are absent.
4	static <T> Optional<T> fromNullable(T nullableReference) If nullableReference is non-null, returns an Optional instance containing that reference; otherwise returns absent().
5	abstract T get() Returns the contained instance, which must be present.
6	abstract int hashCode() Returns a hash code for this instance.
7	abstract boolean isPresent() Returns true if this holder contains a (non-null) instance.
8	static <T> Optional<T> of(T reference) Returns an Optional instance containing the given non-null reference.
9	abstract Optional<T> or(Optional<? extends T> secondChoice) Returns this Optional if it has a value present; secondChoice otherwise.
10	abstract T or(Supplier<? extends T> supplier) Returns the contained instance if it is present; supplier.get() otherwise.
11	abstract T or(T defaultValue) Returns the contained instance if it is present; defaultValue otherwise.
12	abstract T orNull() Returns the contained instance if it is present; null otherwise.
13	static <T> Iterable<T> presentInstances(Iterable<? extends Optional<? extends T>> optionals) Returns the value of each present instance from the supplied optionals, in order, skipping over occurrences of absent().
14	abstract String toString() Returns a string representation for this instance.
15	abstract <V> Optional<V> transform(Function<? super T,V> function) If the instance is present, it is transformed with the given Function; otherwise, absent() is returned.

Methods Inherited

This class inherits methods from the following class −

java.lang.Object

Example of Optional Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import com.google.common.base.Optional;

public class GuavaTester {
   public static void main(String args[]) {
      GuavaTester guavaTester = new GuavaTester();

      Integer value1 =  null;
      Integer value2 =  new Integer(10);
      
      //Optional.fromNullable - allows passed parameter to be null.
      Optional<Integer> a = Optional.fromNullable(value1);
      
      //Optional.of - throws NullPointerException if passed parameter is null
      Optional<Integer> b = Optional.of(value2);		

      System.out.println(guavaTester.sum(a,b));
   }

   public Integer sum(Optional<Integer> a, Optional<Integer> b) {
      //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());

      //Optional.or - returns the value if present otherwise returns
      //the default value passed.
      Integer value1 = a.or(new Integer(0));	

      //Optional.get - gets the value, value should be present
      Integer value2 = b.get();

      return value1 + value2;
   }	
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

First parameter is present: false
Second parameter is present: true
10

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