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 |
|---|---|
| 1 | static <T> Optional<T> empty() – Returns an empty Optional instance. |
| 2 | boolean equals(Object obj) – Indicates whether some other object is “equal to” this Optional. |
| 3 | Optional<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. |
| 5 | T get() – If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException. |
| 6 | int hashCode() – Returns the hash code value of the present value, if any, or 0 (zero) if no value is present. |
| 7 | void ifPresent(Consumer<? super T> consumer) – If a value is present, it invokes the specified consumer with the value, otherwise does nothing. |
| 8 | boolean 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. |
| 10 | static <T> Optional<T> of(T value) – Returns an Optional with the specified present non-null value. |
| 11 | static <T> Optional<T> ofNullable(T value) – Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional. |
| 12 | T orElse(T other) – Returns the value if present, otherwise returns other. |
| 13 | T 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. |
| 15 | String 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