Attribute.java

package evanq.game.utils;


/**
 * An attribute which allows to store a value reference. It may be updated atomically and so is thread-safe.
 *
 * @param <T>   the type of the value it holds.
 */
public interface Attribute<T> {

    /**
     * Returns the key of this attribute.
     */
    AttributeKey<T> key();

    /**
     * Returns the current value, which may be {@code null}
     */
    T get();

    /**
     * Sets the value
     */
    void set(T value);

    /**
     *  Atomically sets to the given value and returns the old value which may be {@code null} if non was set before.
     */
    T getAndSet(T value);

    /**
     *  Atomically sets to the given value if this {@link Attribute} does not contain a value at the moment.
     *  If it was not possible to set the value as it contains a value it will just return the current value.
     */
    T setIfAbsent(T value);

    /**
     * Removes this attribute from the {@link AttributeMap} and returns the old value..  Subsequent {@link #get()}
     * calls will return @{code null}.
     */
    T getAndRemove();

    /**
     * Atomically sets the value to the given updated value if the current value == the expected value.
     * If it the set was successful it returns {@code true} otherwise {@code false}.
     */
    boolean compareAndSet(T oldValue, T newValue);

    /**
     * Removes this attribute from the {@link AttributeMap}.  Subsequent {@link #get()} calls will return @{code null}.
     */
    void remove();
}