ArrayList源码解读

悠悠 2022-04-11 09:25 208阅读 0赞

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);//
        }