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Small extensions for the core Java language libraries.
package net.yetamine.lang.functional;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Stream;
/**
* An alternative to {@link Optional} for the cases when the value may or may
* not be acceptable, but the decision is provided and the container does not
* decide on its own.
*
* @param
* the type of the contained value
*/
public final class Choice implements Supplier {
/** Shared instance for accepted {@code null}. */
private static final Choice ACCEPTED_NULL = new Choice<>(null, true);
/** Shared instance for rejected {@code null}. */
private static final Choice REJECTED_NULL = new Choice<>(null, false);
/** Stored value. */
private final T value;
/** Acceptance flag. */
private final boolean valid;
/**
* Creates a new instance.
*
* @param o
* the value to store
* @param v
* the validity flag
*/
private Choice(T o, boolean v) {
value = o;
valid = v;
}
/**
* Returns an instance representing the value as accepted.
*
* @param
* the type of the value
* @param o
* the value to represent
*
* @return an instance representing the value as accepted
*/
public static Choice accept(T o) {
return (o != null) ? new Choice<>(o, true) : accept();
}
/**
* Returns an instance representing the value as rejected.
*
* @param
* the type of the value
* @param o
* the value to represent
*
* @return an instance representing the value as rejected
*/
public static Choice reject(T o) {
return (o != null) ? new Choice<>(o, false) : reject();
}
/**
* Returns a new instance accepting the value of the given {@link Optional}
* instance, or rejecting {@code null} if the given container is empty.
*
* @param
* the type of the value
* @param optional
* the container of the value to represent. It must not be
* {@code null}.
*
* @return the new instance
*/
@SuppressWarnings("unchecked")
public static Choice of(Optional optional) {
return (Choice) optional.map(Choice::accept).orElseGet(Choice::reject);
}
/**
* Returns a new instance accepting a non-{@code null} values, rejecting
* {@code null}.
*
* @param
* the type of the value
* @param o
* the value to represent
*
* @return the new instance
*/
public static Choice nonNull(T o) {
return (o != null) ? new Choice<>(o, true) : reject();
}
/**
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return String.format("Choice[%s: %s]", valid ? "accepted" : "rejected", value);
}
/**
* @see java.lang.Object#equals(java.lang.Object)
*/
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj instanceof Choice) {
final Choice o = (Choice) obj;
return Objects.equals(value, o.value) && (valid == o.valid);
}
return false;
}
/**
* @see java.lang.Object#hashCode()
*/
@Override
public int hashCode() {
return Objects.hash(value, valid);
}
/**
* Returns the value of this choice.
*
* @return the value of this choice
*
* @see java.util.function.Supplier#get()
*/
public T get() {
return value;
}
/**
* Returns the value of this choice if {@link #isAccepted()}.
*
* @return the value of this choice
*
* @throws NoSuchElementException
* if this choice {@link #isRejected()}
*/
public T require() {
if (isAccepted()) {
return get();
}
throw new NoSuchElementException();
}
/**
* Returns the value of this choice if {@link #isAccepted()}.
*
* @param
* the type of the exception to throw
* @param e
* the supplier of the exception to throw if
* {@link #isRejected()}
*
* @return the value of this choice
*
* @throws X
* if this choice {@link #isRejected()}
*/
public T require(Supplier e) throws X {
if (isAccepted()) {
return get();
}
throw e.get();
}
/**
* Creates a stream of this instance as the only element of the stream.
*
* @return a stream of this instance
*/
public Stream> stream() {
return Stream.of(this);
}
/**
* Returns an {@link Optional} with the value if the value
* {@link #isAccepted()} and not {@code null}.
*
* @return an {@link Optional} with the value, or an empty container if the
* value {@link #isRejected()} or {@code null}
*/
public Optional optional() {
return isAccepted() ? Optional.ofNullable(get()) : Optional.empty();
}
/**
* Returns an instance representing the same value, but with the swapped
* decision, so that when this instance {@link #isAccepted()}, then the
* result {@link #isRejected()}.
*
* @return an swapped instance
*/
public Choice flip() {
return isAccepted() ? reject(get()) : accept(get());
}
/**
* Tests if the value represented by this choice is accepted.
*
* @return {@code true} if the represented value is considered accepted
*/
public boolean isAccepted() {
return valid;
}
/**
* Tests if the value represented by this choice is rejected.
*
* @return {@code false} if the represented value is considered accepted
*/
public boolean isRejected() {
return !isAccepted();
}
/**
* Passes the represented value to the given consumer if
* {@link #isAccepted()} returns {@code true}.
*
* @param consumer
* the consumer to accept the value. It must not be {@code null}.
*
* @return this instance
*/
public Choice ifAccepted(Consumer consumer) {
if (isAccepted()) {
consumer.accept(get());
}
return this;
}
/**
* Runs the given action if {@link #isAccepted()} returns {@code false}.
*
* @param consumer
* the consumer to accept the value. It must not be {@code null}.
*
* @return this instance
*/
public Choice ifRejected(Consumer consumer) {
if (isRejected()) {
consumer.accept(get());
}
return this;
}
/**
* Applies either action depending on {@link #isAccepted()} result.
*
* @param whenAccepted
* the consumer to accept the represented value if
* {@link #isAccepted()}. It must not be {@code null}.
* @param whenRejected
* the consumer to accept the represented value if
* {@link #isRejected()}. It must not be {@code null}.
*
* @return this instance
*/
public Choice consume(Consumer whenAccepted, Consumer whenRejected) {
if (isAccepted()) {
whenAccepted.accept(get());
} else {
whenRejected.accept(get());
}
return this;
}
/**
* Maps this instance.
*
* @param
* the type of the new represented value
* @param f
* the mapping function. It must not be {@code null} and it
* should not return {@code null}.
*
* @return the result of the mapping function
*/
public Choice map(Function, Choice> f) {
return f.apply(this);
}
/**
* Maps the represented value.
*
* @param
* the type of the new value
* @param whenAccepted
* the function to map the represented value if
* {@link #isAccepted()} . It must not be {@code null}.
* @param whenRejected
* the function to map the represented value if
* {@link #isRejected()}. It must not be {@code null}.
*
* @return a new instance represented the mapped value
*/
public Choice map(Function whenAccepted, Function whenRejected) {
return isAccepted() ? accept(whenAccepted.apply(get())) : reject(whenRejected.apply(get()));
}
/**
* Maps the represented value and returns it; this method is a shortcut for
* {@code choice.map(whenAccepted, whenRejected).get()}.
*
* @param
* the type of the new value
* @param whenAccepted
* the function to map the represented value if
* {@link #isAccepted()} . It must not be {@code null}.
* @param whenRejected
* the function to map the represented value if
* {@link #isRejected()}. It must not be {@code null}.
*
* @return the mapped value
*/
public V reconcile(Function whenAccepted, Function whenRejected) {
return isAccepted() ? whenAccepted.apply(get()) : whenRejected.apply(get());
}
/**
* Returns the shared instance representing an accepted {@code null}.
*
* @return the shared instance representing an accepted {@code null}
*/
@SuppressWarnings("unchecked")
private static Choice accept() {
return (Choice) ACCEPTED_NULL;
}
/**
* Returns the shared instance representing rejected {@code null}.
*
* @return the shared instance representing rejected {@code null}
*/
@SuppressWarnings("unchecked")
private static Choice reject() {
return (Choice) REJECTED_NULL;
}
}
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