ArrayList，

ArrayList，

 记录一下关于ArrayList的学习

很久之前学习过ArrayList，翻翻笔记，看到扩容量=原扩容量*3/2+1， 后来想了解一下为什么扩容量是这个，就看了一下源码，返现根本就不是。。可能是JDK版本的原因？  我看的是1.8,所以记录一下

1.属性

//默认容量
private static final int DEFAULT_CAPACITY = 10;

//空数组
private static final Object[] EMPTY_ELEMENTDATA = {};

//默认的空数组
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

//实际存放数据的数组
transient Object[] elementData

//数组大小
private int size;

 

2.add()解析

 
    private static int calculateCapacity(Object[] elementData, int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        return minCapacity;
    }

    private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, 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;
        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);
    }

扩容是在grow方法中，重点是 int newCapacity = oldCapacity+(oldCapacity >> 1) ，说明扩容是原容量+ 原容量/2 也就是原容量的1.5倍。