ArrayList、Vector、HashMap、HashTable是如何擴容

a) ArrayList，默認初始10個大小，每次擴容是原容量的一半，具體代碼如下

public ArrayList() {
this(10);
} 
int newCapacity = (oldCapacity * 3)/2 + 1;

public static native void arraycopy(Object src,  int  srcPos,
                                        Object dest, int destPos,
                                        int length);

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8

b) Vector，默認初始10個大小，每次擴容是原容量的一倍，具體代碼如下：

public Vector() {
this(10);
} 
int newCapacity = (capacityIncrement > 0) ? (oldCapacity + capacityIncrement) : (oldCapacity * 2);

• 1
• 2
• 3
• 4

c) HashMap默認初始16個大小（必須是2的次方），默認每次擴容的因子爲0.75，具體代碼如下：

static final int DEFAULT_INITIAL_CAPACITY = 16; 
static final float DEFAULT_LOAD_FACTOR = 0.75f;
public HashMap() {
  this.loadFactor = DEFAULT_LOAD_FACTOR;
  threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
  table = new Entry[DEFAULT_INITIAL_CAPACITY];
  init();
}

resize(2 * table.length);

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10

d) HashTable默認初始11個大小，默認每次擴容的因子爲0.75

public Hashtable() {
this(11, 0.75f);
}
int newCapacity = oldCapacity * 2 + 1;