arraylist源码

1. 使用默认的进行

源码解析

 List<Integer> list=new ArrayList<Integer>();

// 默认是创建10个长度的
private static final int DEFAULT_CAPACITY = 10;
// 创建的 加上数字
public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }

//扩展
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;
        // 扩大1.5倍
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0) // 比数值小就赋值为数值
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0) // 大于MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; 就赋值为整形的max_value 或者原值
            newCapacity = hugeCapacity(minCapacity);
            // return (minCapacity > MAX_ARRAY_SIZE) ?Integer.MAX_VALUE :  MAX_ARRAY_SIZE;
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
    }