001: package org.tigris.scarab.util;
002:
003: /* ================================================================
004: * Copyright (c) 2000-2002 CollabNet. All rights reserved.
005: *
006: * Redistribution and use in source and binary forms, with or without
007: * modification, are permitted provided that the following conditions are
008: * met:
009: *
010: * 1. Redistributions of source code must retain the above copyright
011: * notice, this list of conditions and the following disclaimer.
012: *
013: * 2. Redistributions in binary form must reproduce the above copyright
014: * notice, this list of conditions and the following disclaimer in the
015: * documentation and/or other materials provided with the distribution.
016: *
017: * 3. The end-user documentation included with the redistribution, if
018: * any, must include the following acknowlegement: "This product includes
019: * software developed by Collab.Net <http://www.Collab.Net/>."
020: * Alternately, this acknowlegement may appear in the software itself, if
021: * and wherever such third-party acknowlegements normally appear.
022: *
023: * 4. The hosted project names must not be used to endorse or promote
024: * products derived from this software without prior written
025: * permission. For written permission, please contact info@collab.net.
026: *
027: * 5. Products derived from this software may not use the "Tigris" or
028: * "Scarab" names nor may "Tigris" or "Scarab" appear in their names without
029: * prior written permission of Collab.Net.
030: *
031: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
032: * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
033: * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
034: * IN NO EVENT SHALL COLLAB.NET OR ITS CONTRIBUTORS BE LIABLE FOR ANY
035: * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
036: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
037: * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
038: * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
039: * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
040: * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
041: * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
042: *
043: * ====================================================================
044: *
045: * This software consists of voluntary contributions made by many
046: * individuals on behalf of Collab.Net.
047: */
048:
049: import java.util.Collections;
050: import java.util.Iterator;
051: import java.util.NoSuchElementException;
052:
053: public class SubsetIterator implements Iterator {
054: public static final SubsetIterator EMPTY = new EmptySubsetIterator();
055:
056: private Iterator i;
057: private final int offset;
058: private final int elements;
059: private int currentPosition;
060:
061: /**
062: * Constructs an itarator on a subset of the given iterator.
063: * The SubsetIterator starts with the offset-element and iterates
064: * over <code>elements</code> elements
065: *
066: * @param i the Iterator to subset
067: * @param offset the position of the first element of the subset
068: * @param element the number of elements the subset should have.
069: */
070: public SubsetIterator(Iterator i, int offset, int elements) {
071:
072: this .i = i;
073: this .offset = offset;
074: this .elements = elements;
075: currentPosition = 0;
076: }
077:
078: /**
079: * Constructs an itarator on a subset of the given iterator.
080: * The SubsetIterator starts with the offset-element and iterates
081: * over all elements
082: *
083: * @param i the Iterator to subset
084: * @param offset the position of the first element of the subset
085: */
086: public SubsetIterator(Iterator i, int offset) {
087: this (i, offset, Integer.MAX_VALUE);
088: }
089:
090: private Boolean hasNext;
091:
092: public boolean hasNext() {
093: if (hasNext == null) {
094: hasNext = (internalIterate()) ? Boolean.TRUE
095: : Boolean.FALSE;
096: }
097: return hasNext.booleanValue();
098: }
099:
100: boolean firstCall = true;
101:
102: private boolean internalIterate() {
103: if (firstCall) {
104: for (int m = 0; i.hasNext() && m < offset; m++) {
105: i.next();
106: }
107: firstCall = false;
108: }
109: currentPosition++;
110: return i.hasNext() && currentPosition <= elements;
111: }
112:
113: public Object next() {
114: if (hasNext()) {
115: hasNext = null;
116: return i.next();
117: } else {
118: throw new NoSuchElementException("Iterator is exhausted"); //EXCEPTION
119: }
120: }
121:
122: public void remove() {
123: i.remove();
124: }
125:
126: }
127:
128: class EmptySubsetIterator extends SubsetIterator {
129: EmptySubsetIterator() {
130: super (Collections.EMPTY_SET.iterator(), 0, 0);
131: }
132:
133: public boolean hasNext() {
134: return false;
135: }
136:
137: public Object next() {
138: throw new NoSuchElementException("This is an empty list."); //EXCEPTION
139: }
140:
141: public void remove() {
142: throw new IllegalStateException(
143: "next() will throw exception, it is "
144: + "not possible to call this method."); //EXCEPTION
145: }
146: }
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