Java Optional or()

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In this guide, you will learn about the Optional or() method in Java programming and how to use it with an example.

1. Optional or() Method Overview

Definition:

The or() method of the Optional class in Java returns an Optional describing the value of the current Optional, if a value is present; otherwise, returns an Optional produced by the supplying function.

Syntax:

public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier)

Parameters:

- supplier: The supplier function that produces an Optional to be returned if the original Optional is empty.

Key Points:

- Introduced in Java 9.

- This method is used to provide a default or alternative Optional if the original Optional is empty.

- The supplying function is only invoked if the original Optional is empty.

- If the supplying function produces a null, a NullPointerException is thrown.

2. Optional or() Method Example

import java.util.Optional;

public class OptionalOrExample {

    public static void main(String[] args) {

        // Creating an Optional object with a value
        Optional<String> valuePresent = Optional.of("Hello World!");

        // Using or() when value is present
        Optional<String> result1 = valuePresent.or(() -> Optional.of("Default Value"));
        System.out.println(result1.get()); // Should print: Hello World!

        // Creating an empty Optional object
        Optional<String> valueAbsent = Optional.empty();

        // Using or() when value is absent
        Optional<String> result2 = valueAbsent.or(() -> Optional.of("Default Value"));
        System.out.println(result2.get()); // Should print: Default Value
    }
}

Output:

Hello World!
Default Value

Explanation:

In the example, we have two Optional objects – valuePresent which holds a String value, and valueAbsent which is empty. 

We use the or() method on both objects. For valuePresent, the original Optional is returned as it has a value. For valueAbsent, the supplying function is invoked, creating a new Optional with the default value, showcasing how or() can be used to provide an alternative Optional in case the original one is empty.

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