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// Part of NoException: https://noexception.machinezoo.com
package com.machinezoo.noexception.optional;
import java.util.*;
import java.util.function.*;
/**
* A container object which may or may not contain a {@code boolean} value.
* If value is present, {@link #isPresent()} will return {@code true} and {@link #getAsBoolean()} will return the value.
*
* Additional methods that depend on the presence or absence of a contained value are provided,
* such as {@link #orElse(boolean)} (return a default value if value is not present)
* and {@link #ifPresent(IntConsumer)} (execute a block of code if the value is present).
*/
public final class OptionalBoolean {
private static final OptionalBoolean empty = new OptionalBoolean(false, false);
private static final OptionalBoolean optionalFalse = new OptionalBoolean(true, false);
private static final OptionalBoolean optionalTrue = new OptionalBoolean(true, true);
private final boolean present;
private final boolean value;
private OptionalBoolean(boolean present, boolean value) {
this.present = present;
this.value = value;
}
/**
* Returns an empty {@code OptionalBoolean} instance.
* No value is present for this {@code OptionalBoolean}.
* There is only one instance of empty {@code OptionalBoolean}.
*
* @return an empty {@code OptionalBoolean}
*/
public static OptionalBoolean empty() {
return empty;
}
/**
* Returns an {@code OptionalBoolean} with the specified value present.
* There are only two global instances of {@code OptionalBoolean} with value present.
* This method just returns one of them.
*
* @param value
* - the value to be present
* @return an {@code OptionalBoolean} with the value present
*/
public static OptionalBoolean of(boolean value) {
return value ? optionalTrue : optionalFalse;
}
/**
* Returns {@code true} if there is a value present, otherwise {@code false}.
*
* @return {@code true} if there is a value present, otherwise {@code false}
*/
public boolean isPresent() {
return present;
}
/**
* If a value is present in this {@code OptionalBoolean}, returns the value, otherwise throws {@code NoSuchElementException}.
*
* @return the value held by this {@code OptionalBoolean}
* @throws NoSuchElementException
* if there is no value present
* @see #isPresent()
*/
public boolean getAsBoolean() {
if (!present)
throw new NoSuchElementException();
return value;
}
/**
* Return the value if present, otherwise return {@code other}.
*
* @param other
* the value to be returned if there is no value present
* @return the value, if present, otherwise {@code other}
*/
public boolean orElse(boolean other) {
return present ? value : other;
}
/**
* Return the value if present, otherwise invoke {@code other} and return the result of that invocation.
*
* @param other
* a {@code BooleanSupplier} whose result is returned if no value is present
* @return the value if present, otherwise the result of {@code other.getAsBoolean()}
* @throws NullPointerException
* if value is not present and {@code other} is {@code null}
*/
public boolean orElseGet(BooleanSupplier other) {
return present ? value : other.getAsBoolean();
}
/**
* Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
* A method reference to the exception constructor with an empty argument list can be used as the supplier.
* For example, {@code IllegalStateException::new}.
*
* @param
* type of the exception to be thrown
* @param exceptionSupplier
* the supplier which will return the exception to be thrown
* @return the present value
* @throws X
* if there is no value present
* @throws NullPointerException
* if no value is present and {@code exceptionSupplier} is {@code null}
*/
public boolean orElseThrow(Supplier exceptionSupplier) throws X {
if (!present)
throw exceptionSupplier.get();
return value;
}
/**
* Have the specified consumer accept the value if a value is present, otherwise do nothing.
* There is no {@code BooleanConsumer} in JDK.
* Value of this {@code OptionalBoolean} is therefore widened to int and passed to {@code IntConsumer}.
* Value of {@code true} is widened to {@code 1}, {@code false} to {@code 0}.
*
* @param consumer
* block to be executed if a value is present
* @throws NullPointerException
* if value is present and {@code consumer} is null
*/
public void ifPresent(IntConsumer consumer) {
if (present)
consumer.accept(value ? 1 : 0);
}
/**
* Indicates whether some other object is "equal to" this {@code OptionalBoolean}.
* The other object is considered equal if it is also an {@code OptionalBoolean}
* and both instances have no value present or the present values are the same.
*
* @param obj
* an object to be tested for equality
* @return {@code true} if the other object is "equal to" this object, otherwise {@code false}
* @see #hashCode()
*/
@Override public boolean equals(Object obj) {
return obj == this;
}
/**
* Returns the hash code value of the present value, if any, or zero if no value is present.
*
* @return hash code value of the present value of 0 if no value is present
* @see #equals(Object)
* @see Boolean#hashCode()
*/
@Override public int hashCode() {
return !present ? 0 : Boolean.hashCode(value);
}
/**
* Returns string representation of this instance suitable for debugging.
* In the current implementation, one of the strings {@code empty}, {@code true}, or {@code false} is returned.
*
* @return the string representation of this instance
*/
@Override public String toString() {
return !present ? "empty" : value ? "true" : "false";
}
}