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Core interfaces and utilities for Blueprints
There is a newer version: 2.6.0
package com.tinkerpop.blueprints.util;

import com.tinkerpop.blueprints.Predicate;
import com.tinkerpop.blueprints.Edge;
import com.tinkerpop.blueprints.Element;
import com.tinkerpop.blueprints.Graph;
import com.tinkerpop.blueprints.GraphQuery;
import com.tinkerpop.blueprints.KeyIndexableGraph;
import com.tinkerpop.blueprints.Vertex;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * For those graph engines that do not support the low-level querying of the vertices or edges, then DefaultGraphQuery can be used.
 * DefaultGraphQuery assumes, at minimum, that Graph.getVertices() and Graph.getEdges() is implemented by the respective Graph.
 *
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public class DefaultGraphQuery extends DefaultQuery implements GraphQuery {

    protected final Graph graph;

    public DefaultGraphQuery(final Graph graph) {
        this.graph = graph;
    }

    public GraphQuery has(final String key) {
        super.has(key);
        return this;
    }

    public GraphQuery hasNot(final String key) {
        super.hasNot(key);
        return this;
    }

    public GraphQuery has(final String key, final Object value) {
        super.has(key, value);
        return this;
    }

    public GraphQuery hasNot(final String key, final Object value) {
        super.hasNot(key, value);
        return this;
    }

    public GraphQuery has(final String key, final Predicate predicate, final Object value) {
        super.has(key, predicate, value);
        return this;
    }

    public > GraphQuery has(final String key, final T value, final Compare compare) {
        super.has(key, compare, value);
        return this;
    }

    public > GraphQuery interval(final String key, final T startValue, final T endValue) {
        super.interval(key, startValue, endValue);
        return this;
    }

    public GraphQuery limit(final int limit) {
        super.limit(limit);
        return this;
    }

    public Iterable edges() {
        return new DefaultGraphQueryIterable(false);
    }

    public Iterable vertices() {
        return new DefaultGraphQueryIterable(true);
    }

    protected class DefaultGraphQueryIterable implements Iterable {

        private Iterable iterable = null;

        public DefaultGraphQueryIterable(final boolean forVertex) {
            this.iterable = (Iterable) getElementIterable(forVertex ? Vertex.class : Edge.class);
        }

        public Iterator iterator() {
            return new Iterator() {
                T nextElement = null;
                final Iterator itty = iterable.iterator();
                long count = 0;

                public boolean hasNext() {
                    if (null != this.nextElement) {
                        return true;
                    } else {
                        return this.loadNext();
                    }
                }

                public T next() {
                    while (true) {
                        if (this.nextElement != null) {
                            final T temp = this.nextElement;
                            this.nextElement = null;
                            return temp;
                        }

                        if (!this.loadNext())
                            throw new NoSuchElementException();
                    }
                }

                public void remove() {
                    throw new UnsupportedOperationException();
                }

                private boolean loadNext() {
                    this.nextElement = null;
                    if (this.count > limit) return false;
                    while (this.itty.hasNext()) {
                        final T element = this.itty.next();
                        boolean filter = false;

                        for (final HasContainer hasContainer : hasContainers) {
                            if (!hasContainer.isLegal(element)) {
                                filter = true;
                                break;
                            }
                        }

                        if (!filter) {
                            if (++this.count <= limit) {
                                this.nextElement = element;
                                return true;
                            }
                        }

                    }
                    return false;
                }
            };
        }

        private Iterable getElementIterable(final Class elementClass) {
            if (graph instanceof KeyIndexableGraph) {
                final Set keys = getIndexedKeys(elementClass);
                HasContainer container = null;
                for (final HasContainer hasContainer : hasContainers) {
                    if (hasContainer.predicate.equals(com.tinkerpop.blueprints.Compare.EQUAL) && keys.contains(hasContainer.key)) {
                        container = hasContainer;
                        break;
                    }
                }
                if (container != null) {
                    if (Vertex.class.isAssignableFrom(elementClass))
                        return graph.getVertices(container.key, container.value);
                    else
                        return graph.getEdges(container.key, container.value);
                }
            }

            if (Vertex.class.isAssignableFrom(elementClass))
                return graph.getVertices();
            else
                return graph.getEdges();
        }

        protected Set getIndexedKeys(final Class elementClass) {
          return ((KeyIndexableGraph) graph).getIndexedKeys(elementClass);
        }
        
    }

}