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// »ñÈ¡key¶ÔÓ¦µÄvalue public V get(Object key) { if (key == null) return getForNullKey(); // »ñÈ¡keyµÄhashÖµ int hash = hash(key.hashCode()); // ÔÚ“¸ÃhashÖµ¶ÔÓ¦µÄÁ´±í”ÉϲéÕÒ“¼üÖµµÈÓÚkey”µÄÔªËØ for (Entrye = table[indexFor(hash, table.length)]; e != null; e = e.next) { Object k; //ÅжÏkeyÊÇ·ñÏàͬ if (e.hash == hash && ((k = e.key) == key || key.equals(k))) return e.value; } //ûÕÒµ½Ôò·µ»Ønull return null; } // »ñÈ¡“keyΪnull”µÄÔªËØµÄÖµ // HashMap½«“keyΪnull”µÄÔªËØ´æ´¢ÔÚtable[0]λÖ㬵«²»Ò»¶¨ÊǸÃÁ´±íµÄµÚÒ»¸öλÖã¡ private V getForNullKey() { for (Entry e = table[0]; e != null; e = e.next) { if (e.key == null) return e.value; } return null; }
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// ½«“key-value”Ìí¼Óµ½HashMapÖÐ public V put(K key, V value) { // Èô“keyΪnull”£¬Ôò½«¸Ã¼üÖµ¶ÔÌí¼Óµ½table[0]ÖС£ if (key == null) return putForNullKey(value); // Èô“key²»Îªnull”£¬Ôò¼ÆËã¸ÃkeyµÄ¹þÏ£Öµ£¬È»ºó½«ÆäÌí¼Óµ½¸Ã¹þÏ£Öµ¶ÔÓ¦µÄÁ´±íÖС£ int hash = hash(key.hashCode()); int i = indexFor(hash, table.length); for (Entrye = table[i]; e != null; e = e.next) { Object k; // Èô“¸Ãkey”¶ÔÓ¦µÄ¼üÖµ¶ÔÒѾ´æÔÚ£¬ÔòÓÃеÄvalueÈ¡´ú¾ÉµÄvalue¡£È»ºóÍ˳ö£¡ if (e.hash == hash && ((k = e.key) == key || key.equals(k))) { V oldValue = e.value; e.value = value; e.recordAccess(this); return oldValue; } } // Èô“¸Ãkey”¶ÔÓ¦µÄ¼üÖµ¶Ô²»´æÔÚ£¬Ôò½«“key-value”Ìí¼Óµ½tableÖÐ modCount++; //½«key-valueÌí¼Óµ½table[i]´¦ addEntry(hash, key, value, i); return null; }
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// putForNullKey()µÄ×÷ÓÃÊǽ«“keyΪnull”¼üÖµ¶ÔÌí¼Óµ½table[0]λÖà private V putForNullKey(V value) { for (Entrye = table[0]; e != null; e = e.next) { if (e.key == null) { V oldValue = e.value; e.value = value; e.recordAccess(this); return oldValue; } } // Èç¹ûûÓдæÔÚkeyΪnullµÄ¼üÖµ¶Ô£¬ÔòÖ±½ÓÌâ°¢¼ûµ½table[0]´¦! modCount++; addEntry(0, null, value, 0); return null; }
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// ÐÂÔöEntry¡£½«“key-value”²åÈëÖ¸¶¨Î»Öã¬bucketIndexÊÇλÖÃË÷Òý¡£ void addEntry(int hash, K key, V value, int bucketIndex) { // ±£´æ“bucketIndex”λÖõÄÖµµ½“e”ÖÐ Entrye = table[bucketIndex]; // ÉèÖÓbucketIndex”λÖõÄÔªËØÎª“ÐÂEntry”£¬ // ÉèÖÓe”Ϊ“ÐÂEntryµÄÏÂÒ»¸ö½Úµã” table[bucketIndex] = new Entry (hash, key, value, e); // ÈôHashMapµÄʵ¼Ê´óС ²»Ð¡ÓÚ “ãÐÖµ”£¬Ôòµ÷ÕûHashMapµÄ´óС if (size++ >= threshold) resize(2 * table.length); }
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// ÖØÐµ÷ÕûHashMapµÄ´óС£¬newCapacityÊǵ÷ÕûºóµÄµ¥Î» void resize(int newCapacity) { Entry[] oldTable = table; int oldCapacity = oldTable.length; if (oldCapacity == MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return; } // н¨Ò»¸öHashMap£¬½«“¾ÉHashMap”µÄÈ«²¿ÔªËØÌí¼Óµ½“ÐÂHashMap”ÖУ¬ // È»ºó£¬½«“ÐÂHashMap”¸³Öµ¸ø“¾ÉHashMap”¡£ Entry[] newTable = new Entry[newCapacity]; transfer(newTable); table = newTable; threshold = (int)(newCapacity * loadFactor); }
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// ½«HashMapÖеÄÈ«²¿ÔªËض¼Ìí¼Óµ½newTableÖÐ void transfer(Entry[] newTable) { Entry[] src = table; int newCapacity = newTable.length; for (int j = 0; j < src.length; j++) { Entrye = src[j]; if (e != null) { src[j] = null; do { Entry next = e.next; int i = indexFor(e.hash, newCapacity); e.next = newTable[i]; newTable[i] = e; e = next; } while (e != null); } } }
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