In Java, the Optional class provides methods for handling values that may or may not be present. The methods ifPresent and ifPresentOrElse are particularly useful for executing code conditionally based on whether a value is present in the Optional.

1. Using ifPresent

The ifPresent method executes a Consumer when the value is present (i.e., it’s not null). If the Optional is empty, it does nothing. This is useful when you only want to handle the presence of a value and don’t need any fallback action when the value is absent.

Example:

package org.kodejava.util;

import java.util.Optional;

public class OptionalIfPresentExample {
    public static void main(String[] args) {
        // Create an Optional with a value
        Optional<String> optionalValue = Optional.of("Hello, Optional!");

        // Execute only if a value is present
        optionalValue.ifPresent(value -> System.out.println("Value is: " + value));

        // Create an empty Optional
        Optional<String> emptyOptional = Optional.empty();

        // Nothing happens here
        emptyOptional.ifPresent(value -> System.out.println("This won't be printed."));
    }
}

Output:

Value is: Hello, Optional!

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2. Using ifPresentOrElse

The ifPresentOrElse method executes a Consumer if the value is present, and executes a Runnable if the value is absent. This is helpful if you want to handle both cases (presence and absence) explicitly.

Example:

package org.kodejava.util;

import java.util.Optional;

public class OptionalIfPresentOrElseExample {
    public static void main(String[] args) {
        // Create an Optional with a value
        Optional<String> optionalValue = Optional.of("Hello, Optional!");

        // Execute the consumer if the value is present, otherwise execute the runnable
        optionalValue.ifPresentOrElse(
                value -> System.out.println("Value is: " + value),
                () -> System.out.println("Value is not present")
        );

        // Create an empty Optional
        Optional<String> emptyOptional = Optional.empty();

        // Handle the absence of value
        emptyOptional.ifPresentOrElse(
                value -> System.out.println("This won't be printed."),
                () -> System.out.println("Value is not present")
        );
    }
}

Output:

Value is: Hello, Optional!
Value is not present

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Key Differences:

1. ifPresent: Only executes when the value is present. It doesn’t account for the absent case.
2. ifPresentOrElse: Handles both the presence and absence cases, allowing you to define fallback behavior when the value is missing.

Use case:

• Use ifPresent when you only care about taking action if the value is present.
• Use ifPresentOrElse when you also want to explicitly perform some alternate action if the value is absent.