java ArrayList源码分析（转载）

ArrayList<String> list = new ArrayList<String>();
list.add("语文: 99");
list.add("数学: 98");
list.add("英语: 100");
list.remove(0);

public boolean add(E e) {
 ensureCapacityInternal(size + 1); // Increments modCount!!
 elementData[size++] = e;
 return true;
}

private void ensureCapacityInternal(int minCapacity) {
 if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
 }

 ensureExplicitCapacity(minCapacity);
}

private void ensureExplicitCapacity(int minCapacity) {
 modCount++;

 // overflow-conscious code
 if (minCapacity - elementData.length > 0)
 grow(minCapacity);
}

private void grow(int minCapacity) {
 // overflow-conscious code
 int oldCapacity = elementData.length;
 // 扩展为原来的1.5倍
 int newCapacity = oldCapacity + (oldCapacity >> 1);
 // 如果扩为1.5倍还不满足需求，直接扩为需求值
 if (newCapacity - minCapacity < 0)
 newCapacity = minCapacity;
 if (newCapacity - MAX_ARRAY_SIZE > 0)
 newCapacity = hugeCapacity(minCapacity);
 // minCapacity is usually close to size, so this is a win:
 elementData = Arrays.copyOf(elementData, newCapacity);
}

public E set(int index, E element) {
 rangeCheck(index);

 E oldValue = elementData(index);
 elementData[index] = element;
 return oldValue;
}

public E get(int index) {
 rangeCheck(index);

 return elementData(index);
}

public E remove(int index) {
 rangeCheck(index);

 modCount++;
 E oldValue = elementData(index);

 int numMoved = size - index - 1;
 if (numMoved > 0)
 // 把后面的往前移
 System.arraycopy(elementData, index+1, elementData, index,
 numMoved);
 // 把最后的置null
 elementData[--size] = null; // clear to let GC do its work

 return oldValue;
}