1 /* 2 * Copyright (C) 2012 Google Inc. 3 * Licensed to The Android Open Source Project. 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package com.android.mail.utils; 19 20 import com.google.common.collect.Lists; 21 import com.google.common.collect.Maps; 22 23 import java.util.Deque; 24 import java.util.Map; 25 26 /** 27 * A Map of Deques. Each entry at key K has a deque of values V. 28 * 29 */ 30 public class DequeMap<K, V> { 31 32 public interface Visitor<V> { 33 void visit(V item); 34 } 35 36 private final Map<K, Deque<V>> mMap = Maps.newHashMap(); 37 38 /** 39 * Add a value V to the deque stored under key K. 40 * 41 */ 42 public void add(K key, V item) { 43 Deque<V> pile = mMap.get(key); 44 if (pile == null) { 45 pile = Lists.newLinkedList(); 46 mMap.put(key, pile); 47 } 48 pile.add(item); 49 } 50 51 /** 52 * Removes and returns the first value V from the deque of Vs for key K, or null if no such Vs 53 * exist. 54 * 55 * @see Deque#poll() 56 * 57 * @param key 58 * @return a V, or null 59 */ 60 public V poll(K key) { 61 final Deque<V> pile = mMap.get(key); 62 if (pile == null) { 63 return null; 64 } 65 return pile.poll(); 66 } 67 68 /** 69 * Returns, but does not remove, the first value V from the deque of Vs for key K, or null if 70 * no such Vs exist. 71 * 72 * @see Deque#peek() 73 * 74 * @param key 75 * @return a V, or null 76 */ 77 public V peek(K key) { 78 final Deque<V> pile = mMap.get(key); 79 if (pile == null) { 80 return null; 81 } 82 return pile.peek(); 83 } 84 85 public void clear() { 86 mMap.clear(); 87 } 88 89 /** 90 * Allows a {@link Visitor} to operate on each value V in this structure, irrespective of each 91 * value's key. Modifying this map during iteration is not supported. Iteration order is not 92 * guaranteed. 93 * 94 * @param visitor 95 */ 96 // An iterator would also suffice, but this is easier to write and understand. 97 public void visitAll(Visitor<V> visitor) { 98 for (Map.Entry<K, Deque<V>> entry : mMap.entrySet()) { 99 for (V item : entry.getValue()) { 100 visitor.visit(item); 101 } 102 } 103 } 104 105 } 106
