ArrayList源码解读

ArrayList继承了AbstractList类记忆实现了List接口，使用数组保存元素

public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
    private static final long serialVersionUID = 8683452581122892189L;

    private static final int DEFAULT_CAPACITY = 10;//数组默认大小

    private static final Object[] EMPTY_ELEMENTDATA = {};//初始化数据
    private transient Object[] elementData;//保存数据的数组

当使用无参的构造器时，数组大小默认10个。

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

        ensureExplicitCapacity(minCapacity);
    }

 

添加数据时会检查数组容量大小，如果数组容量比数据个数小，那么数组容量会以原来的1.5倍增加，并且会重排数据。

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);//原来的1.5倍
        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);//
    }