ArrayList源码分析 add（E e）

最新推荐文章于 2024-04-17 15:38:13 发布

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最新推荐文章于 2024-04-17 15:38:13 发布

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本文详细解析了Java中ArrayList的add方法实现原理。介绍了ArrayList如何通过调整容量来存储新增元素，并确保内部数组能够容纳更多的数据。文章还深入探讨了ArrayList如何在达到初始容量限制时进行扩容，以及扩容过程中涉及的内存分配和数据复制过程。

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add（E e）方法

*存储ArrayList元素的数组缓冲区。
* ArrayList的容量是这个数组缓冲区的长度。任何
*带有elementData的空ArrayList == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
*当添加第一个元素时，*将被扩展到DEFAULT_CAPACITY。
 
transient Object[] elementData;

private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

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

private static final int DEFAULT_CAPACITY = 10;

  //默认0
 private int size;
  




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

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


private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError();
        return (minCapacity > MAX_ARRAY_SIZE) ?
            Integer.MAX_VALUE :
            MAX_ARRAY_SIZE;
    }

//Arrays 工具类方法
public static <T> T[] copyOf(T[] original, int newLength) {
        return (T[]) copyOf(original, newLength, original.getClass());
    }