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Java Artificial Life Simulation Engine
There is a newer version: 1.1.0
package jalse.misc;

import java.util.Objects;
import java.util.UUID;
import java.util.function.Predicate;

/**
 * This is for anything that should be uniquely identifiable within JALSE. This interface allows for
 * easy equality and comparison.
 *
 * @author Elliot Ford
 *
 */
public interface Identifiable {

    /**
     * A hard-coded dummy ID that can be used to identify an Identifiable that does not need to be
     * unique (not advised). ID = {@code 00000000-0000-0000-0000-000000000000}.
     */
    UUID DUMMY_ID = new UUID(0, 0);

    /**
     * Checks if the two identifiable objects are equals using their unique identifiers.
     *
     * @param a
     *            First object.
     * @param b
     *            Second object.
     * @return Whether the unique identifiers are equal.
     */
    static boolean equals(final Identifiable a, final Object b) {
	return a == b || a != null && b instanceof Identifiable
		&& Objects.equals(a.getID(), ((Identifiable) b).getID());
    }

    /**
     * Gets the ID of the object if it is an Identifiable.
     *
     * @param obj
     *            Object to get ID for.
     * @return ID of object if Identifiable instance otherwise return null.
     */
    static UUID getID(final Object obj) {
	return obj instanceof Identifiable ? ((Identifiable) obj).getID() : null;
    }

    /**
     * Generates a hashcode for an identifiable.
     *
     * @param obj
     *            Identifiable instance.
     * @return Hashcode for the identifiable or {@code 0} if null.
     */
    static int hashCode(final Identifiable obj) {
	return obj == null ? 0 : Objects.hashCode(obj.getID());
    }

    /**
     * Predicate to check if the identifiable is equal to that supplied.
     *
     * @param obj
     *            Identifiable to check for.
     * @return Predicate of {@code true} if the identifiable is equal or {@code false} if it is not.
     *
     * @see Identifiable#equals(Identifiable, Object)
     */
    static Predicate is(final Identifiable obj) {
	return i -> equals(obj, i);
    }

    /**
     * Predicate to check if the identifiable is not equal to that supplied.
     *
     * @param obj
     *            Identifiable to check against.
     * @return Predicate of {@code false} if the identifiable is equal or {@code true} if it is.
     *
     * @see Identifiable#getID()
     */
    static Predicate not(final Identifiable obj) {
	return is(obj).negate();
    }

    /**
     * Creates a simple to string for the identifiable. This is structured like
     * {@code  [id=X]}.
     *
     * @param obj
     *            Identifiable to create a string representation for.
     * @return String representation of the identifiable.
     */
    static String toString(final Identifiable obj) {
	return obj.getClass().getSimpleName() + " [id=" + obj.getID() + "]";
    }

    /**
     * Gets the unique identifier.
     *
     * @return This objects identifier.
     */
    UUID getID();
}