HashTable源码分析
/**
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The hash table data.
*/
//存放键值对的数组
private transient Entry,?>[] table;/**
The total number of entries in the hash table.
*/
//大小
private transient int count;/**
- The table is rehashed when its size exceeds this threshold. (The
- value of this field is (int)(capacity * loadFactor).)
@serial
*/
//阀值
private int threshold;/**
- The load factor for the hashtable.
@serial
*/
//负载因子
private float loadFactor;
//默认初始容量为11,负载因子0.75
public Hashtable() {
this(11, 0.75f);
}//1.8版本没有修改,没有维护红黑树结构
public synchronized V put(K key, V value) {
// Make sure the value is not null
if (value == null) {
throw new NullPointerException();
}// Makes sure the key is not already in the hashtable. Entry,?> tab[] = table; int hash = key.hashCode(); //求余获得索引 int index = (hash & 0x7FFFFFFF) % tab.length; @SuppressWarnings("unchecked") Entry
entry = (Entry )tab[index]; for(; entry != null ; entry = entry.next) { if ((entry.hash == hash) && entry.key.equals(key)) { V old = entry.value; entry.value = value; return old; } } addEntry(hash, key, value, index); return null; }
/**
- Removes the key (and its corresponding value) from this
- hashtable. This method does nothing if the key is not in the hashtable.
- @param key the key that needs to be removed
- @return the value to which the key had been mapped in this hashtable,
- or
null
if the key did not have a mapping - @throws NullPointerException if the key is
null
*/
public synchronized V remove(Object key) {
Entry,?> tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;@SuppressWarnings("unchecked")
br/>@SuppressWarnings("unchecked")
e = (Entry)tab[index];
for(Entryprev = null ; e != null ; prev = e, e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
modCount++;
if (prev != null) {
prev.next = e.next;
} else {
tab[index] = e.next;
}
count--;
V oldValue = e.value;
e.value = null;
return oldValue;
}
}
return null;
}
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