com.tinkerpop.gremlin.process.Step Maven / Gradle / Ivy

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package com.tinkerpop.gremlin.process;

import java.io.Serializable;
import java.util.Iterator;

/**
 * A {@link Step} denotes a unit of computation within a {@link Traversal}.
 * A step takes an incoming object and yields an outgoing object.
 * Steps are chained together in a {@link Traversal} to yield a lazy function chain of computation.
 *
 * @param  The incoming object type of the step
 * @param  The outgoing object type of the step
 */
public interface Step extends Iterator>, Serializable, Cloneable {

    /**
     * A token object that denotes "nothing" and is used to declare an empty spot in a {@link Traversal}
     */
    public static final NoObject NO_OBJECT = new NoObject();

    /**
     * Add a collection of {@link Traverser} objects of type S to the head of the step.
     *
     * @param iterator The iterator of objects to add
     */
    public void addStarts(final Iterator> iterator);

    /**
     * Set the step that is previous to the current step.
     * Used for linking steps together to form a function chain.
     *
     * @param step the previous step of this step
     */
    public void setPreviousStep(final Step step);

    /**
     * Get the step prior to the current step.
     *
     * @return The previous step
     */
    public Step getPreviousStep();

    /**
     * Set the step that is next to the current step.
     * Used for linking steps together to form a function chain.
     *
     * @param step the next step of this step
     */
    public void setNextStep(final Step step);

    /**
     * Get the next step to the current step.
     *
     * @return The next step
     */
    public Step getNextStep();

    /**
     * Get the {@link Traversal} that this step is contained within.
     *
     * @param  The incoming object type of the traversal
     * @param  The outgoing object type of the traversal
     * @return The traversal of this step
     */
    public  Traversal getTraversal();

    /**
     * Cloning is used to duplicate steps for the purpose of traversal optimization.
     *
     * @return The cloned step
     * @throws CloneNotSupportedException
     */
    public Object clone() throws CloneNotSupportedException;

    /**
     * Get the as-label of this step.
     *
     * @return the as-label of the step
     */
    public String getAs();

    /**
     * Set the as-label of this step.
     *
     * @param as the as-label for this step
     */
    public void setAs(final String as);

    static final class NoObject {

        private NoObject() {
        }

        public boolean equals(final Object object) {
            return object instanceof NoObject;
        }

        public int hashCode() {
            return 1212121212;
        }
    }
}