Programming TIPS!

A site on Java API Examples and TIPS.
All Posts
Japanese Site

Java : Optional with Examples

January 31, 2024 May 3, 2022

Optional (Java SE 21 & JDK 21) with Examples.
You will find code examples on most Optional methods.


Summary

A container object which may or may not contain a non-null value. If a value is present, isPresent() returns true. If no value is present, the object is considered empty and isPresent() returns false.

Optional (Java SE 21 & JDK 21)

Class diagram

API examples on this page uses the Sample class below.

public class Sample<T> {

    private final T value;

    public Sample(T value) {
        this.value = value;
    }

    public Optional<T> getValue() {
        return Optional.ofNullable(value);
    }
}

final var sample = new Sample<>("abcd");

sample.getValue().ifPresent(value -> {
    System.out.println("value : " + value);
});

// Result
// ↓
//value : abcd

final var sample = new Sample<>(null);

sample.getValue().ifPresentOrElse(value -> {
    System.out.println("value : " + value);
}, () -> {
    System.out.println("value : null!");
});

// Result
// ↓
//value : null!

Methods

static <T> Optional<T> empty ()

Returns an empty Optional instance.

Optional (Java SE 21 & JDK 21) 
final var opt = Optional.empty();

System.out.println(opt); // Optional.empty
System.out.println(opt.isEmpty()); // true
//opt.orElseThrow(); // NoSuchElementException: No value present

boolean equals (Object obj)

Indicates whether some other object is "equal to" this Optional.

Optional (Java SE 21 & JDK 21) 
final var opt1 = Optional.of(100);
final var opt2 = Optional.of(100);
final var opt3 = Optional.of(999);

System.out.println(opt1.equals(opt2)); // true
System.out.println(opt1.equals(opt3)); // false

final var opt1 = Optional.of("abcd");
final var opt2 = Optional.of("XYZ");

System.out.println(opt1.equals(opt2)); // false

final var opt1 = Optional.empty();
final var opt2 = Optional.empty();

System.out.println(opt1.equals(opt2)); // true

Optional<T> filter (Predicate<? super T> predicate)

If a value is present, and the value matches the given predicate, returns an Optional describing the value, otherwise returns an empty Optional.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret1 = sample.getValue().filter(s -> {
    System.out.println("filter : " + s);
    return s.equals("abcd");
});
System.out.println("ret : " + ret1);

// Result
// ↓
//filter : abcd
//ret : Optional[abcd]

final var ret2 = sample.getValue().filter(s -> {
    System.out.println("filter : " + s);
    return s.equals("XYZ");
});
System.out.println("ret : " + ret2);

// Result
// ↓
//filter : abcd
//ret : Optional.empty

final var sample = new Sample<>(null);

final var ret = sample.getValue().filter(s -> {
    System.out.println("filter : " + s);
    return s.equals("abcd");
});
System.out.println("ret : " + ret);

// Result
// ↓
//ret : Optional.empty

<U> Optional<U> flatMap (Function<? super T,? extends Optional<? extends U>> mapper)

If a value is present, returns the result of applying the given Optional-bearing mapping function to the value, otherwise returns an empty Optional.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret = sample.getValue().flatMap(s -> {
    System.out.println("flatMap : " + s);
    return Optional.of(s.toUpperCase());
});

System.out.println("ret : " + ret);

// Result
// ↓
//flatMap : abcd
//ret : Optional[ABCD]

final var sample = new Sample<>(255);

final var ret1 = sample.getValue().flatMap(i -> {
    System.out.println("flatMap : " + i);
    return Optional.of(i * 2);
});

System.out.println("ret : " + ret1);

// Result
// ↓
//flatMap : 255
//ret : Optional[510]

final var ret2 = sample.getValue().flatMap(i -> {
    System.out.println("flatMap : " + i);
    return Optional.of("0x" + Integer.toHexString(i));
});

System.out.println("ret : " + ret2);

// Result
// ↓
//flatMap : 255
//ret : Optional[0xff]

final var sample = new Sample<>(null);

final var ret = sample.getValue().flatMap(s -> {
    System.out.println("flatMap : " + s);
    return Optional.empty();
});

System.out.println("ret : " + ret);

// Result
// ↓
//ret : Optional.empty

T get ()

If a value is present, returns the value, otherwise throws NoSuchElementException.

Optional (Java SE 21 & JDK 21)

The preferred alternative to this method is orElseThrow().

final var sample = new Sample<>("abcd");

final var opt = sample.getValue();
if (opt.isPresent()) {
    System.out.println(opt.get()); // abcd
}

final var sample = new Sample<>(null);

//sample.getValue().get(); // NoSuchElementException: No value present

int hashCode ()

Returns the hash code of the value, if present, otherwise 0 (zero) if no value is present.

Optional (Java SE 21 & JDK 21) 
System.out.println(Optional.empty().hashCode()); // 0

System.out.println(Optional.of(123).hashCode()); // 123

System.out.println("abcd".hashCode()); // 2987074
System.out.println(Optional.of("abcd").hashCode()); // 2987074

void ifPresent (Consumer<? super T> action)

If a value is present, performs the given action with the value, otherwise does nothing.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

sample.getValue().ifPresent(value -> {
    System.out.println("action : " + value);
});

// Result
// ↓
//action : abcd

final var sample = new Sample<>(null);

sample.getValue().ifPresent(value -> {
    System.out.println("action : " + value);
});

// Result
// ↓
//<No output>

void ifPresentOrElse (Consumer<? super T> action, Runnable emptyAction)

If a value is present, performs the given action with the value, otherwise performs the given empty-based action.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

sample.getValue().ifPresentOrElse(value -> {
    System.out.println("action : " + value);
}, () -> {
    System.out.println("emptyAction!");
});

// Result
// ↓
//action : abcd

final var sample = new Sample<>(null);

sample.getValue().ifPresentOrElse(value -> {
    System.out.println("action : " + value);
}, () -> {
    System.out.println("emptyAction!");
});

// Result
// ↓
//emptyAction!

boolean isEmpty ()

If a value is not present, returns true, otherwise false.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

if (sample.getValue().isEmpty()) {
    System.out.println("empty!");
} else {
    System.out.println("present!");
}

// Result
// ↓
//present!

final var sample = new Sample<>(null);

if (sample.getValue().isEmpty()) {
    System.out.println("empty!");
} else {
    System.out.println("present!");
}

// Result
// ↓
//empty!

boolean isPresent ()

If a value is present, returns true, otherwise false.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

if (sample.getValue().isPresent()) {
    System.out.println("present!");
} else {
    System.out.println("empty!");
}

// Result
// ↓
//present!

final var sample = new Sample<>(null);

if (sample.getValue().isPresent()) {
    System.out.println("present!");
} else {
    System.out.println("empty!");
}

// Result
// ↓
//empty!

<U> Optional<U> map (Function<? super T,? extends U> mapper)

If a value is present, returns an Optional describing (as if by ofNullable(T)) the result of applying the given mapping function to the value, otherwise returns an empty Optional.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret = sample.getValue().map(s -> {
    System.out.println("map : " + s);
    return s.toUpperCase();
});

System.out.println("ret : " + ret);

// Result
// ↓
//map : abcd
//ret : Optional[ABCD]

final var ret2 = sample.getValue().map(s -> {
    System.out.println("map : " + s);
    return null;
});

System.out.println("ret : " + ret2);

// Result
// ↓
//map : abcd
//ret : Optional.empty

final var sample = new Sample<>(255);

final var ret1 = sample.getValue().map(i -> {
    System.out.println("map : " + i);
    return i * 2;
});

System.out.println("ret : " + ret1);

// Result
// ↓
//map : 255
//ret : Optional[510]

final var ret2 = sample.getValue().map(i -> {
    System.out.println("map : " + i);
    return "0x" + Integer.toHexString(i);
});

System.out.println("ret : " + ret2);

// Result
// ↓
//map : 255
//ret : Optional[0xff]

final var sample = new Sample<String>(null);

final var ret = sample.getValue().map(s -> {
    System.out.println("map : " + s);
    return s.toUpperCase();
});

System.out.println("ret : " + ret);

// Result
// ↓
//ret : Optional.empty

static <T> Optional<T> of (T value)

Returns an Optional describing the given non-null value.

Optional (Java SE 21 & JDK 21) 
final var opt1 = Optional.of(123);
System.out.println(opt1); // Optional[123]

final var opt2 = Optional.of("abc");
System.out.println(opt2); // Optional[abc]

//Optional.of(null); // NullPointerException

static <T> Optional<T> ofNullable (T value)

Returns an Optional describing the given value, if non-null, otherwise returns an empty Optional.

Optional (Java SE 21 & JDK 21) 
final var opt1 = Optional.ofNullable(123);
System.out.println(opt1); // Optional[123]

final var opt2 = Optional.ofNullable("abc");
System.out.println(opt2); // Optional[abc]

final var opt3 = Optional.ofNullable(null);
System.out.println(opt3); // Optional.empty

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

If a value is present, returns an Optional describing the value, otherwise returns an Optional produced by the supplying function.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret = sample.getValue().or(() -> {
    System.out.println("or action!");
    return Optional.of("XYZ");
});

System.out.println("ret : " + ret);

// Result
// ↓
//ret : Optional[abcd]

final var sample = new Sample<>(null);

final var ret = sample.getValue().or(() -> {
    System.out.println("or action!");
    return Optional.of("XYZ");
});

System.out.println("ret : " + ret);

// Result
// ↓
//or action!
//ret : Optional[XYZ]

T orElse (T other)

If a value is present, returns the value, otherwise returns other.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret = sample.getValue().orElse("XYZ");
System.out.println(ret); // abcd

final var sample = new Sample<>(null);

final var ret = sample.getValue().orElse("XYZ");
System.out.println(ret); // XYZ

T orElseGet (Supplier<? extends T> supplier)

If a value is present, returns the value, otherwise returns the result produced by the supplying function.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret = sample.getValue().orElseGet(() -> {
    System.out.println("or action!");
    return "XYZ";
});

System.out.println("ret : " + ret);

// Result
// ↓
//ret : abcd

final var sample = new Sample<>(null);

final var ret = sample.getValue().orElseGet(() -> {
    System.out.println("or action!");
    return "XYZ";
});

System.out.println("ret : " + ret);

// Result
// ↓
//or action!
//ret : XYZ

T orElseThrow ()

If a value is present, returns the value, otherwise throws NoSuchElementException.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var opt = sample.getValue();
if (opt.isPresent()) {
    System.out.println(opt.orElseThrow()); // abcd
}

final var sample = new Sample<>(null);

//sample.getValue().orElseThrow(); // NoSuchElementException: No value present

<X extends Throwable> T orElseThrow (Supplier<? extends X> exceptionSupplier)

If a value is present, returns the value, otherwise throws an exception produced by the exception supplying function.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var opt = sample.getValue();
if (opt.isPresent()) {
    System.out.println(opt.orElseThrow(IllegalStateException::new)); // abcd
}

final var sample = new Sample<>(null);

try {
    sample.getValue().orElseThrow(() -> {
        throw new IllegalStateException("optional is empty");
    });
} catch (IllegalStateException e) {
    System.out.println(e);
}

// Result
// ↓
//java.lang.IllegalStateException: optional is empty

Stream<T> stream ()

If a value is present, returns a sequential Stream containing only that value, otherwise returns an empty Stream.

Optional (Java SE 21 & JDK 21) 
final var sample = new Sample<>("abcd");

final var ret1 = sample.getValue().stream().toList();
System.out.println(ret1); // [abcd]

final var ret2 = sample.getValue().stream().count();
System.out.println(ret2); // 1

final var sample = new Sample<>(null);

final var ret1 = sample.getValue().stream().toList();
System.out.println(ret1); // []

final var ret2 = sample.getValue().stream().count();
System.out.println(ret2); // 0

String toString ()

Returns a non-empty string representation of this Optional suitable for debugging.

Optional (Java SE 21 & JDK 21) 
final var ret1 = Optional.empty().toString();
System.out.println(ret1); // Optional.empty

final var ret2 = Optional.of(123).toString();
System.out.println(ret2); // Optional[123]

final var ret3 = Optional.of("abc").toString();
System.out.println(ret3); // Optional[abc]

Related posts

To top of page