ArrayList如何扩容？

最新推荐文章于 2025-06-03 19:00:00 发布

转载最新推荐文章于 2025-06-03 19:00:00 发布 · 324 阅读

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原文链接：http://www.cnblogs.com/qiananshiguang/p/10299654.html

本文深入解析了Java中ArrayList集合的内部实现，特别是其扩容机制。初始容量为10，当元素数量超过当前容量时，ArrayList会自动将容量增加到原容量的1.5倍。通过源码分析，揭示了ArrayList如何高效地管理和调整其内部数组的大小。

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1、调用ArrayList的参构造方法，此时集合内部是一个空数组

transient Object[] elementData;
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}

2、初次调用add方法，数组的容量初始化为10，每次数组容量不够时，数组的大小扩展为原来的1.5倍，newCapacity = oldCapacity + (oldCapacity >> 1)

private int size;

private static final int DEFAULT_CAPACITY = 10;

protected transient int modCount = 0;

private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

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

private void ensureExplicitCapacity(int minCapacity) {
    modCount++;
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}

private void grow(int minCapacity) {
    int oldCapacity = elementData.length;
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
    elementData = Arrays.copyOf(elementData, newCapacity);
}

转载于:https://www.cnblogs.com/qiananshiguang/p/10299654.html