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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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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();
    }
}