Hashtable是线程安全的;先看其构造方法
/** * Constructs a new, empty hashtable with a default initial capacity (11) * and load factor (0.75). */ public Hashtable() { this(11, 0.75f); }
初始大小为11,扩容百分比为0.75;
另外研究期put方法
/** * Maps the specified <code>key</code> to the specified * <code>value</code> in this hashtable. Neither the key nor the * value can be <code>null</code>. <p> * * The value can be retrieved by calling the <code>get</code> method * with a key that is equal to the original key. * * @param key the hashtable key * @param value the value * @return the previous value of the specified key in this hashtable, * or <code>null</code> if it did not have one * @exception NullPointerException if the key or value is * <code>null</code> * @see Object#equals(Object) * @see #get(Object) */ 1.public synchronized V put(K key, V value) { // Make sure the value is not null 2 if (value == null) { throw new NullPointerException(); } // Makes sure the key is not already in the hashtable. 3 Entry tab[] = table; 4 int hash = hash(key); 5 int index = (hash & 0x7FFFFFFF) % tab.length; 6 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { 7 if ((e.hash == hash) && e.key.equals(key)) { 8 V old = e.value; 9 e.value = value; 10 return old; } } 11 modCount++; 12 if (count >= threshold) { // Rehash the table if the threshold is exceeded 13 rehash(); 14 tab = table; 15 hash = hash(key); 16 index = (hash & 0x7FFFFFFF) % tab.length; 17 } // Creates the new entry. 18 Entry<K,V> e = tab[index]; 19 tab[index] = new Entry<>(hash, key, value, e); 20 count++; 21 return null; }
第1行表明它的并发是通过synchronized来加锁;第2行描述value值不能为空;
第4行得到其hash值；第5到10计算put的逻辑过程；
第11-17表明当容量超过因子时，进行扩容的计算；
我的学习暂时到此
