《Java设计模式深入讲解分析项目实战》（完整版）

变量

size ArrayList实际个数

transient Object[] elementData;储存数组

private static final int DEFAULT_CAPACITY = 10;默认个数是10个

构造方法

1. public ArrayList() {

2. this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;

3. }

1. public ArrayList(int initialCapacity) {

2. if (initialCapacity > 0) {

3. this.elementData = new Object[initialCapacity];

4. } else if (initialCapacity == 0) {

5. this.elementData = EMPTY_ELEMENTDATA;

6. } else {

7. throw new IllegalArgumentException("Illegal Capacity: "+

8. initialCapacity);

9. }

10. }

它是如何扩展的呢

1. private void grow(int minCapacity) {

2. // overflow-conscious code

3. int oldCapacity = elementData.length;

4. int newCapacity = oldCapacity + (oldCapacity >> 1);

5. if (newCapacity - minCapacity < 0)

6. newCapacity = minCapacity;

7. if (newCapacity - MAX_ARRAY_SIZE > 0)

8. newCapacity = hugeCapacity(minCapacity);

9. // minCapacity is usually close to size, so this is a win:

10. elementData = Arrays.copyOf(elementData, newCapacity);

11. }

一般发生在什么时候，add的时候进行调用，扩展是1.5倍

add方法

1. public boolean add(E e) {

2. ensureCapacityInternal(size + 1); // Increments modCount!!

3. elementData[size++] = e;

4. return true;

5. }

1. public void add(int index, E element) {

2. rangeCheckForAdd(index);

3.  

4. ensureCapacityInternal(size + 1); // Increments modCount!!

5. System.arraycopy(elementData, index, elementData, index + 1,

6. size - index);

7. elementData[index] = element;

8. size++;

9. }

rangeCheckForAdd是看看索引会不会越界，ensureCapacityInternal看看是否需要扩容

remove的话将数组某下标设置为空

一般使用for循环去遍历的