java - 无法理解在 Java 中调整 ArrayList 大小时溢出的可能性

Question

引用自 JDK 7 的代码片段 java.util.ArrayList类让我感到困惑。我终生无法理解它怎么可能导致溢出。我感到困惑的区域标有 <--- what do they mean by this? .有人可以帮助我理解这种逻辑可能溢出的情况吗？ TIA。

public void ensureCapacity(int minCapacity) {
    if (minCapacity > 0)
        ensureCapacityInternal(minCapacity);
}  

private void ensureCapacityInternal(int minCapacity) {
    modCount++;
    // overflow-conscious code <--- what do they mean by this?
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}

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

private void grow(int minCapacity) {
    // overflow-conscious code <--- what do they mean by this?
    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 <--- what do they mean by this?
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
        MAX_ARRAY_SIZE;
}

编辑:我主要担心的是:hugeCapacity 怎么会收到负数？

Answer 1

当计算值大于其类型允许的字节数时，会导致溢出。

在 oldCapacity 值被分配给 newCapacity 执行一些操作后，如果这些操作导致某些值不适合 int那么就会发生溢出。我想这就是为什么这段代码被评论为溢出有意识的代码。