Java 集合系列（二）ArrayList详解

/**   * Appends the specified element to the end of this list.   *   * @param e element to be appended to this list   * @return <tt>true</tt> (as specified by {@link Collection#add})   */  public boolean add(E e) {    ensureCapacityInternal(size + 1);  // 进行扩容校验    elementData[size++] = e;      // 将值添加到数组后面，并将 size+1    return true;  }  /**   * The array buffer into which the elements of the ArrayList are stored.   * The capacity of the ArrayList is the length of this array buffer. Any   * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA   * will be expanded to DEFAULT_CAPACITY when the first element is added.   */  transient Object[] elementData; // non-private to simplify nested class access    private void ensureCapacityInternal(int minCapacity) {    ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));  // elementData 数组  }  /**   * Default initial capacity.   */  private static final int DEFAULT_CAPACITY = 10;    /**   * Shared empty array instance used for default sized empty instances. We   * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when   * first element is added.   */  private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};  // 返回最大的 index  private static int calculateCapacity(Object[] elementData, int minCapacity) {    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {  // 与空数组实例对比      return Math.max(DEFAULT_CAPACITY, minCapacity);    }    return minCapacity;  }  private void ensureExplicitCapacity(int minCapacity) {    modCount++;    // overflow-conscious code    if (minCapacity - elementData.length > 0)      grow(minCapacity);  }

/**   * Increases the capacity to ensure that it can hold at least the   * number of elements specified by the minimum capacity argument.   *   * @param minCapacity the desired minimum capacity   */  private void grow(int minCapacity) {    // overflow-conscious code    int oldCapacity = elementData.length;    int newCapacity = oldCapacity + (oldCapacity >> 1);    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);  }

/**   * Inserts the specified element at the specified position in this   * list. Shifts the element currently at that position (if any) and   * any subsequent elements to the right (adds one to their indices).   *   * @param index index at which the specified element is to be inserted   * @param element element to be inserted   * @throws IndexOutOfBoundsException {@inheritDoc}   */  public void add(int index, E element) {    rangeCheckForAdd(index);  // 校验index是否超过当前定义的数组大小范围，超过则抛出 IndexOutOfBoundsException    ensureCapacityInternal(size + 1); // Increments modCount!!    System.arraycopy(elementData, index, elementData, index + 1,             size - index);   // 复制，向后移动    elementData[index] = element;    size++;  }    /**   * A version of rangeCheck used by add and addAll.   */  private void rangeCheckForAdd(int index) {    if (index > size || index < 0)      throw new IndexOutOfBoundsException(outOfBoundsMsg(index));  }