Creating and Reading Optional · Optional in Java | Java

Create

Method	Use when
`Optional.of(value)`	value is surely not null (throws NPE if it is)
`Optional.ofNullable(value)`	value may be null
`Optional.empty()`	no value

Read

Method	Behaviour when empty
`orElse(other)`	returns other (other is always evaluated)
`orElseGet(supplier)`	calls supplier only when empty (lazy)
`orElseThrow()` / `orElseThrow(supplier)`	throws NoSuchElementException / your exception
`ifPresent(consumer)`	does nothing
`ifPresentOrElse(consumer, runnable)`	runs the runnable
`isPresent()`, `isEmpty()`	false / true
`get()`	throws — avoid; use orElseThrow() instead

orElse vs orElseGet

Example

orElse always runs its argument, even when a value is present. Use orElseGet for anything expensive (DB call, object creation).

import java.util.*;

public class Main {
    static String loadDefaultFromDb() {
        System.out.println("  (expensive DB call!)");
        return "default-city";
    }

    public static void main(String[] args) {
        Optional<String> city = Optional.of("Hyderabad");

        System.out.println("orElse:");
        System.out.println(city.orElse(loadDefaultFromDb()));

        System.out.println("orElseGet:");
        System.out.println(city.orElseGet(Main::loadDefaultFromDb));

        Optional<String> empty = Optional.empty();
        empty.ifPresentOrElse(c -> System.out.println("City " + c), () -> System.out.println("No city set"));
        System.out.println("isEmpty: " + empty.isEmpty());

        try {
            empty.orElseThrow(() -> new IllegalArgumentException("City is required"));
        } catch (IllegalArgumentException e) {
            System.out.println("Caught: " + e.getMessage());
        }
    }
}

Output

orElse:
  (expensive DB call!)
Hyderabad
orElseGet:
Hyderabad
No city set
isEmpty: true
Caught: City is required