自己实现HashMap集合
如图，HashMap的结果就是这个样子。横向是链表，纵向是数组。所以hashmap是由数组和链表组成的。
下面来实现HashMap
1 import java.util.Collection; 2 import java.util.Map; 3 import java.util.Set; 4 5 public class HashMapTemplate<K,V> implements Map<K,V>{ 6 //初始大小 7 private int capacity = 16; 8 private int size = 0; 9 Entity<K,V>[] entities=null; 10 11 @Override 12 public void clear() { 13 // TODO Auto-generated method stub 14 entities=null; 15 } 16 17 @Override 18 public boolean containsKey(Object key) { 19 //处理key为null的情况 20 if (key==null) { 21 Entity entity=entities[0]; 22 if (entity==null) { 23 return false; 24 }else { 25 if (entity.getKey()==key) { 26 return true; 27 }else{ 28 while(entity.getNextEntity()!=null){ 29 if (entity.getNextEntity().getKey().equals(key)) { 30 return true; 31 } 32 entity=entity.getNextEntity(); 33 } 34 return false; 35 } 36 } 37 }else{ 38 int index=key.hashCode()%capacity; 39 Entity entity=entities[index]; 40 if (entity.getKey().equals(key)) { 41 return true; 42 }else { 43 while(entity.getNextEntity()!=null){ 44 if (entity.getNextEntity().getKey().equals(key)) { 45 return true; 46 } 47 entity=entity.getNextEntity(); 48 } 49 return false; 50 51 } 52 } 53 } 54 55 @Override 56 public boolean containsValue(Object value) { 57 // TODO Auto-generated method stub 58 return false; 59 } 60 61 @Override 62 public Set<java.util.Map.Entry<K, V>> entrySet() { 63 // TODO Auto-generated method stub 64 return null; 65 } 66 67 @Override 68 public V get(Object key) { 69 if (key==null) { 70 Entity entity=entities[0]; 71 if (entity.getKey()==key) { 72 return (V) entity.getValue(); 73 }else { 74 while(entity.getNextEntity()!=null){ 75 if (entity.getNextEntity().getKey().equals(key)) { 76 return (V) entity.getValue(); 77 } 78 entity=entity.getNextEntity(); 79 } 80 return null; 81 82 } 83 }else{ 84 int index=key.hashCode()%capacity; 85 Entity entity=entities[index]; 86 if (entity.getKey().equals(key)) { 87 return (V) entity.getValue(); 88 }else { 89 while(entity.getNextEntity()!=null){ 90 if (entity.getNextEntity().getKey().equals(key)) { 91 return (V) entity.getValue(); 92 } 93 entity=entity.getNextEntity(); 94 } 95 return null; 96 97 } 98 } 99 } 100 101 @Override 102 public boolean isEmpty() { 103 // TODO Auto-generated method stub 104 return false; 105 } 106 107 @Override 108 public Set<K> keySet() { 109 // TODO Auto-generated method stub 110 return null; 111 } 112 113 @Override 114 public V put(K key, V value) { 115 reCapacity(); 116 Entity<K, V> newEntity = new Entity<K, V>(key, value); 117 put(newEntity, this.entities, this.capacity); 118 return null; 119 } 120 private void put(Entity<K, V> newEntity, Entity<K, V>[] entities, int capacity) { 121 if (newEntity.getKey()==null) { 122 Entity entity=entities[0]; 123 if (entity==null) { 124 entities[0]=newEntity; 125 size++; 126 } 127 }else{ 128 int index=newEntity.getKey().hashCode()%capacity; 129 Entity entity=entities[index]; 130 Entity firstEntity =entities[index]; 131 if (entity==null) { 132 entities[index]=newEntity; 133 size++; 134 }else { 135 if (newEntity.getKey().equals(entity.getKey())) { 136 newEntity.setNextEntity(entity.getNextEntity()); 137 newEntity.setPreEntity(entity.getPreEntity()); 138 if (entity.getNextEntity()!=null) { 139 entity.getNextEntity().setPreEntity(newEntity); 140 } 141 entities[index]=newEntity; 142 }else if (entity.getNextEntity()!=null) { 143 while (entity.getNextEntity()!=null) { 144 entity = entity.getNextEntity(); 145 if (newEntity.getKey().equals(entity.getKey())) { 146 newEntity.setPreEntity(entity.getPreEntity()); 147 newEntity.setNextEntity(entity.getNextEntity()); 148 if (entity.getNextEntity() != null) { 149 entity.getNextEntity().setPreEntity(newEntity); 150 } 151 entities[index] = newEntity; 152 } 153 } 154 newEntity.setNextEntity(firstEntity); 155 newEntity.setPreEntity(firstEntity.getPreEntity()); 156 firstEntity.setPreEntity(newEntity); 157 entities[index] = newEntity; 158 size++; 159 }else { 160 newEntity.setNextEntity(firstEntity); 161 firstEntity.setPreEntity(newEntity); 162 entities[index] = newEntity; 163 size++; 164 } 165 } 166 } 167 } 168 @Override 169 public void putAll(Map<? extends K, ? extends V> m) { 170 // TODO Auto-generated method stub 171 172 } 173 174 @Override 175 public V remove(Object key) { 176 // TODO Auto-generated method stub 177 return null; 178 } 179 180 @Override 181 public int size() { 182 // TODO Auto-generated method stub 183 return this.size; 184 } 185 186 @Override 187 public Collection<V> values() { 188 // TODO Auto-generated method stub 189 return null; 190 } 191 public HashMapTemplate() { 192 //初始化容量 193 entities = new Entity[capacity]; 194 } 195 /** 196 * 扩容 197 */ 198 private void reCapacity() { 199 if (size >= capacity) { 200 int newCapacity = capacity * 2; 201 @SuppressWarnings("unchecked") 202 Entity<K, V>[] newEntities = new Entity[newCapacity]; 203 for (int i = 0; i < capacity; i++) { 204 Entity<K, V> entity = entities[i]; 205 while (entity != null) { 206 put(entity, newEntities, newCapacity); 207 entity = entity.getNextEntity(); 208 } 209 } 210 this.capacity = newCapacity; 211 this.entities = newEntities; 212 } 213 } 214 215 @Override 216 public String toString() { 217 StringBuilder sb = new StringBuilder(); 218 for (int i = 0; i < capacity; i++) { 219 sb.append("index=").append(i).append("["); 220 boolean hasEntity = false; 221 Entity<K, V> entity = entities[i]; 222 if (entity != null) { 223 hasEntity = true; 224 } 225 while (entity != null) { 226 sb.append("[").append(entity.getKey()).append("=").append(entity.getValue()).append("]").append(","); 227 entity = entity.getNextEntity(); 228 } 229 if (hasEntity) { 230 sb.deleteCharAt(sb.length() - 1); 231 } 232 sb.append("]\n"); 233 } 234 return sb.toString(); 235 } 236 } 237 @SuppressWarnings("unchecked") 238 class Entity<K,V>{ 239 private K key; 240 private V value; 241 private Entity<K,V> PreEntity;//前节点 242 private Entity<K,V> nextEntity;//后节点 243 244 public K getKey() { 245 return key; 246 } 247 public void setKey(K key) { 248 this.key = key; 249 } 250 public V getValue() { 251 return value; 252 } 253 public void setValue(V value) { 254 this.value = value; 255 } 256 257 public Entity getPreEntity() { 258 return PreEntity; 259 } 260 261 public void setPreEntity(Entity preEntity) { 262 PreEntity = preEntity; 263 } 264 public Entity getNextEntity() { 265 return nextEntity; 266 } 267 public void setNextEntity(Entity nextEntity) { 268 this.nextEntity = nextEntity; 269 } 270 public Entity(K k,V v){ 271 this.key=k; 272 this.value=v; 273 } 274 275 }
上面有一个点需要注意一下：
1.HashMap允许key为null，所以需要处理一下
2.HashMap存放键值对的时候，需要检查容量是否充足，但是因为我们这里是引用传递，所以需要单独写一个put方法通过局部变量的临近原则解决对象的问题。
3.完成hashmap部分功能。并没有完全写完。
