Java : OptionalDouble with Examples

public class DoubleSample {

    private final double value;

    public DoubleSample() {
        this.value = -1.0;
    }

    public DoubleSample(double value) {
        if (value < 0.0) {
            throw new IllegalArgumentException();
        }

        this.value = value;
    }

    public OptionalDouble getValue() {
        if (value < 0.0) {
            return OptionalDouble.empty();
        } else {
            return OptionalDouble.of(value);
        }
    }
}

final var sample = new DoubleSample(1.23);

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

// Result
// ↓
//value : 1.23

final var sample = new DoubleSample();

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

// Result
// ↓
//value : empty!

static OptionalDouble empty ()

Returns an empty OptionalDouble instance.

final var opt = OptionalDouble.empty();
System.out.println(opt); // OptionalDouble.empty
System.out.println(opt.isEmpty()); // true

final var opt = OptionalDouble.empty();

try {
    final var value = opt.orElseThrow();
} catch (NoSuchElementException e) {
    System.out.println(e);
}

// Result
// ↓
//java.util.NoSuchElementException: No value present

boolean equals (Object obj)

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

final var opt1 = OptionalDouble.of(100.0);
final var opt2 = OptionalDouble.of(100.0);
final var opt3 = OptionalDouble.of(999.0);

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

final var opt1 = OptionalDouble.of(1.23);
final var opt2 = OptionalDouble.empty();

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

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

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

double getAsDouble ()

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

final var sample = new DoubleSample(1.23);

final var opt = sample.getValue();
if (opt.isPresent()) {
    System.out.println(opt.getAsDouble()); // 1.23
}

final var sample = new DoubleSample();
final var opt = sample.getValue();

try {
    final var value = opt.getAsDouble();
} catch (NoSuchElementException e) {
    System.out.println(e);
}

// Result
// ↓
//java.util.NoSuchElementException: No value present

int hashCode ()

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

final var ret1 = OptionalDouble.empty().hashCode();
System.out.println(ret1); // 0

final var ret2 = OptionalDouble.of(1.23).hashCode();
System.out.println(ret2); // 1158867386

final var ret3 = OptionalDouble.of(-0.789).hashCode();
System.out.println(ret3); // 1383618319

void ifPresent (DoubleConsumer action)

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

final var sample = new DoubleSample(1.23);

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

System.out.println("-- end --");

// Result
// ↓
//-- ifPresent --
//  action : 1.23
//-- end --

final var sample = new DoubleSample();

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

System.out.println("-- end --");

// Result
// ↓
//-- ifPresent --
//-- end --

void ifPresentOrElse (DoubleConsumer action, Runnable emptyAction)

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

final var sample = new DoubleSample(1.23);

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

System.out.println("-- end --");

// Result
// ↓
//-- ifPresentOrElse --
//  action : 1.23
//-- end --

final var sample = new DoubleSample();

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

System.out.println("-- end --");

// Result
// ↓
//-- ifPresentOrElse --
//  emptyAction!
//-- end --

boolean isEmpty ()

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

final var sample = new DoubleSample(1.23);

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

// Result
// ↓
//present!

final var sample = new DoubleSample();

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.

final var sample = new DoubleSample(1.23);

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

// Result
// ↓
//present!

final var sample = new DoubleSample();

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

// Result
// ↓
//empty!

static OptionalDouble of (double value)

Returns an OptionalDouble describing the given value.

final var opt1 = OptionalDouble.of(1.23);
System.out.println(opt1); // OptionalDouble[1.23]

final var opt2 = OptionalDouble.of(-0.789);
System.out.println(opt2); // OptionalDouble[-0.789]

double orElse (double other)

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

final var sample = new DoubleSample(100.0);

final var ret = sample.getValue().orElse(9999.0);
System.out.println(ret); // 100.0

final var sample = new DoubleSample();

final var ret = sample.getValue().orElse(9999.0);
System.out.println(ret); // 9999.0

double orElseGet (DoubleSupplier supplier)

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

final var sample = new DoubleSample(100.0);

final var ret = sample.getValue().orElseGet(() -> {
    System.out.println("action!");
    return 9999.0;
});

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

// Result
// ↓
//ret = 100.0

final var sample = new DoubleSample();

final var ret = sample.getValue().orElseGet(() -> {
    System.out.println("action!");
    return 9999.0;
});

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

// Result
// ↓
//action!
//ret = 9999.0

double orElseThrow ()

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

final var sample = new DoubleSample(1.23);

final var opt = sample.getValue();
if (opt.isPresent()) {
    System.out.println(opt.orElseThrow()); // 1.23
}

final var sample = new DoubleSample();
final var opt = sample.getValue();

try {
    final var value = opt.orElseThrow();
} catch (NoSuchElementException e) {
    System.out.println(e);
}

// Result
// ↓
//java.util.NoSuchElementException: No value present

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

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

final var sample = new DoubleSample(1.23);

final var opt = sample.getValue();
if (opt.isPresent()) {
    final var value = opt.orElseThrow(IllegalStateException::new);
    System.out.println(value); // 1.23
}

final var sample = new DoubleSample();

try {
    final var value = sample.getValue().orElseThrow(() -> {
        throw new IllegalStateException("empty!");
    });
} catch (IllegalStateException e) {
    System.out.println(e);
}

// Result
// ↓
//java.lang.IllegalStateException: empty!

DoubleStream stream ()

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

final var sample = new DoubleSample(1.23);

final var array = sample.getValue().stream().toArray();
System.out.println(Arrays.toString(array)); // [1.23]

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

final var sample = new DoubleSample();

final var array = sample.getValue().stream().toArray();
System.out.println(Arrays.toString(array)); // []

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

String toString ()

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

final var ret1 = OptionalDouble.empty().toString();
System.out.println(ret1); // OptionalDouble.empty

final var ret2 = OptionalDouble.of(1.23).toString();
System.out.println(ret2); // OptionalDouble[1.23]

final var ret3 = OptionalDouble.of(-0.789).toString();
System.out.println(ret3); // OptionalDouble[-0.789]