jdk7 中HashMap的知识点总结

static final int DEFAULT_INITIAL_CAPACITY = 16;

static final int MAXIMUM_CAPACITY = 1 << 30;

static final float DEFAULT_LOAD_FACTOR = 0.75f;

transient Entry<K,V>[] table;

//capacity * load factor,超过这个数就会进行再哈希
int threshold;

static class Entry<K,V> implements Map.Entry<K,V> {
 final K key;
 V value;
 Entry<K,V> next;
 int hash;

 /**
  * Creates new entry.
  */
 Entry(int h, K k, V v, Entry<K,V> n) {
  value = v;
  next = n;
  key = k;
  hash = h;
 }
 ...

public V put(K key, V value) {
 if (key == null)
  return putForNullKey(value);
 int hash = hash(key);
 int i = indexFor(hash, table.length);
 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
  Object k;
  if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
  V oldValue = e.value;
  e.value = value;
  e.recordAccess(this);
  return oldValue;
  }
 }

 modCount++;
 addEntry(hash, key, value, i);
 return null;
 }

final int hash(Object k) {
 int h = 0;
 h ^= k.hashCode();

 h ^= (h >>> 20) ^ (h >>> 12);
 return h ^ (h >>> 7) ^ (h >>> 4);
 }

static int indexFor(int h, int length) {
 return h & (length-1);
 }

 private V putForNullKey(V value) {
 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
  if (e.key == null) {
  V oldValue = e.value;
  e.value = value;
  e.recordAccess(this);
  return oldValue;
  }
 }
 modCount++;
 addEntry(0, null, value, 0);
 return null;
 }

void addEntry(int hash, K key, V value, int bucketIndex) {
 if ((size >= threshold) && (null != table[bucketIndex])) {
  resize(2 * table.length);
  hash = (null != key) ? hash(key) : 0;
  bucketIndex = indexFor(hash, table.length);
 }

 createEntry(hash, key, value, bucketIndex);
 }

void createEntry(int hash, K key, V value, int bucketIndex) {
 Entry<K,V> e = table[bucketIndex];
 table[bucketIndex] = new Entry<>(hash, key, value, e);
 size++;
 }

public V get(Object key) {
 if (key == null)
  return getForNullKey();
 Entry<K,V> entry = getEntry(key);

 return null == entry ? null : entry.getValue();
 }

private V getForNullKey() {
 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
  if (e.key == null)
  return e.value;
 }
 return null;
 }

final Entry<K,V> getEntry(Object key) {
 int hash = (key == null) ? 0 : hash(key);
 for (Entry<K,V> e = table[indexFor(hash, table.length)];
  e != null;
  e = e.next) {
  Object k;
  if (e.hash == hash &&
  ((k = e.key) == key || (key != null && key.equals(k))))
  return e;
 }
 return null;
 }