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XML Schema Object Model (XSOM) is a Java library that allows applications to easily parse XML Schema documents and inspect information in them. It is expected to be useful for applications that need to take XML Schema as an input.
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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * 
 * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
 * 
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License. You can obtain
 * a copy of the License at https://glassfish.dev.java.net/public/CDDL+GPL.html
 * or glassfish/bootstrap/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 * 
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at glassfish/bootstrap/legal/LICENSE.txt.
 * Sun designates this particular file as subject to the "Classpath" exception
 * as provided by Sun in the GPL Version 2 section of the License file that
 * accompanied this code.  If applicable, add the following below the License
 * Header, with the fields enclosed by brackets [] replaced by your own
 * identifying information: "Portions Copyrighted [year]
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 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
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 */

package com.sun.xml.xsom.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * {@link Collection} that returns the view of objects which are actually fetched
 * lazily from an {@link Iterator}.
 *
 * @author Kohsuke Kawaguchi
 */
public class DeferedCollection implements Collection {
    /**
     * The iterator that lazily evaluates SCD query.
     */
    private final Iterator result;

    /**
     * Stores values that are already fetched from {@link #result}.
     */
    private final List archive = new ArrayList();

    public DeferedCollection(Iterator result) {
        this.result = result;
    }

    public boolean isEmpty() {
        if(archive.isEmpty())
            fetch();
        return archive.isEmpty();
    }

    public int size() {
        fetchAll();
        return archive.size();
    }

    public boolean contains(Object o) {
        if(archive.contains(o))
            return true;
        while(result.hasNext()) {
            T value = result.next();
            archive.add(value);
            if(value.equals(o))
                return true;
        }
        return false;
    }

    public boolean containsAll(Collection c) {
        for (Object o : c) {
            if(!contains(o))
                return false;
        }
        return true;
    }

    public Iterator iterator() {
        return new Iterator() {
            int idx=0;
            public boolean hasNext() {
                if(idxT[] toArray(T[] a) {
        fetchAll();
        return archive.toArray(a);
    }



    private void fetchAll() {
        while(result.hasNext())
            archive.add(result.next());
    }

    /**
     * Fetches another item from {@link
     */
    private void fetch() {
        if(result.hasNext())
            archive.add(result.next());
    }

// mutation methods are unsupported
    public boolean add(T o) {
        throw new UnsupportedOperationException();
    }

    public boolean remove(Object o) {
        throw new UnsupportedOperationException();
    }

    public boolean addAll(Collection c) {
        throw new UnsupportedOperationException();
    }

    public boolean removeAll(Collection c) {
        throw new UnsupportedOperationException();
    }

    public boolean retainAll(Collection c) {
        throw new UnsupportedOperationException();
    }

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