1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.giraph.utils; 20 21 import com.google.common.collect.Lists; 22 23 import java.util.List; 24 25 /** 26 * Collection to keep pairs in, without creating a wrapper object around 27 * each pair of objects. 28 * 29 * @param <U> Type of the first element in a pair 30 * @param <V> Type of the second element in a pair 31 */ 32 public class PairList<U, V> { 33 /** List to keep first elements of pairs in */ 34 protected List<U> firstList; 35 /** List to keep second elements of pairs in */ 36 protected List<V> secondList; 37 38 /** 39 * Constructor 40 */ 41 public PairList() { 42 } 43 44 /** 45 * Initialize the inner state. Must be called before {@code add()} is 46 * called. 47 */ 48 public void initialize() { 49 firstList = Lists.newArrayList(); 50 secondList = Lists.newArrayList(); 51 } 52 53 54 /** 55 * Initialize the inner state, with a known size. Must be called before 56 * {@code add()} is called. 57 * 58 * @param size Number of pairs which will be added to the list 59 */ 60 public void initialize(int size) { 61 firstList = Lists.newArrayListWithCapacity(size); 62 secondList = Lists.newArrayListWithCapacity(size); 63 } 64 65 /** 66 * Add a pair to the collection. 67 * 68 * @param first First element of the pair 69 * @param second Second element of the pair 70 */ 71 public void add(U first, V second) { 72 firstList.add(first); 73 secondList.add(second); 74 } 75 76 /** 77 * Get number of pairs in this list. 78 * 79 * @return Number of pairs in the list 80 */ 81 public int getSize() { 82 return firstList.size(); 83 } 84 85 /** 86 * Check if the list is empty. 87 * 88 * @return True iff there are no pairs in the list 89 */ 90 public boolean isEmpty() { 91 return getSize() == 0; 92 } 93 94 /** 95 * Get iterator through elements of this object. 96 * 97 * @return {@link Iterator} iterator 98 */ 99 public Iterator getIterator() { 100 return new Iterator(); 101 } 102 103 /** 104 * Special iterator class which we'll use to iterate through elements of 105 * {@link PairList}, without having to create new object as wrapper for 106 * each pair. 107 * 108 * Protocol is somewhat similar to the protocol of {@link java.util.Iterator} 109 * only here next() doesn't return the next object, it just moves along in 110 * the collection. Values related to current pair can be retrieved by calling 111 * getCurrentFirst() and getCurrentSecond() methods. 112 * 113 * Not thread-safe. 114 */ 115 public class Iterator { 116 /** Current position of the iterator */ 117 private int position = -1; 118 119 /** 120 * Returns true if the iteration has more elements. 121 * 122 * @return True if the iteration has more elements. 123 */ 124 public boolean hasNext() { 125 return position < getSize() - 1; 126 } 127 128 /** 129 * Moves to the next element in the iteration. 130 */ 131 public void next() { 132 position++; 133 } 134 135 /** 136 * Get first element of the current pair of the iteration. 137 * 138 * @return First element of the current pair of the iteration 139 */ 140 public U getCurrentFirst() { 141 return firstList.get(position); 142 } 143 144 /** 145 * Get second element of the current pair of the iteration. 146 * 147 * @return Second element of the current pair of the iteration 148 */ 149 public V getCurrentSecond() { 150 return secondList.get(position); 151 } 152 } 153 }