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Core interfaces and utilities for Blueprints

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package com.tinkerpop.blueprints;

import java.util.Collection;

/**
 * Contains is a predicate that evaluates whether the first object is contained within (or not within) the second collection object.
 * For example:
 *
 *   gremlin IN [gremlin, blueprints, furnace] == true
 *   gremlin NOT_IN [gremlin, rexster] == false
 *   rexster NOT_IN [gremlin, blueprints, furnace] == true
 *
 * @author Pierre De Wilde
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public enum Contains implements Predicate {

    IN, NOT_IN;

    public boolean evaluate(final Object first, final Object second) {
        if (second instanceof Collection) {
            return this.equals(IN) ? ((Collection) second).contains(first) : !((Collection) second).contains(first);
        } else {
            throw new IllegalArgumentException("The second argument must be a collection");
        }
    }

    public Contains opposite() {
        return this.equals(IN) ? NOT_IN : IN;
    }
}