初始化
ArrayList的底层是一个动态数组,ArrayList首先会对传进来的初始化参数initalCapacity进行判断
扩容时机
当数组的大小大于初始容量的时候(比如初始为10,当添加第11个元素的时候),就会进行扩容,新的容量为旧的容量的1.5倍。
扩容方式
扩容的时候,会以新的容量建一个原数组的拷贝,修改原数组,指向这个新数组,原数组被抛弃,会被GC回收。
/ArraList初始化容量判断 public void ensureCapacity(int minCapacity) { int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) ? 0 : DEFAULT_CAPACITY; if (minCapacity > minExpand) { ensureExplicitCapacity(minCapacity); } } //添加元素的方法 public boolean add(E e) { ensureCapacityInternal(size + 1); // Increments modCount!! elementData[size++] = e; return true; } //判断是否需要扩容 private void ensureExplicitCapacity(int minCapacity) { modCount++; // overflow-conscious code if (minCapacity - elementData.length > 0) grow(minCapacity); } //扩容的机制 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);
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https://blog.csdn.net/zhou920786312/article/details/83750032
原文:https://www.cnblogs.com/Jomini/p/13783395.html