list clear() 和 =[] 和 =null 问题

list clear() 和 =[] 和 =null 问题

• clear() 释放list 里面所有对象 ,不管是哪个实现类的clear 方式都是将里面的所有元素都释放了并且清空里面的属性,List对象是存在的
• ArrayList 源码如下

    public void clear() {
        modCount++;

        // clear to let GC do its work
        for (int i = 0; i < size; i++)
            elementData[i] = null;

        size = 0;
    }

• LinkedList 源码如下

    public void clear() {
        // Clearing all of the links between nodes is "unnecessary", but:
        // - helps a generational GC if the discarded nodes inhabit
        //   more than one generation
        // - is sure to free memory even if there is a reachable Iterator
        for (Node<E> x = first; x != null; ) {
            Node<E> next = x.next;
            x.item = null;
            x.next = null;
            x.prev = null;
            x = next;
        }
        first = last = null;
        size = 0;
        modCount++;
    }

• = null 释放数组对象，里面所引用的对象也就释放了。
• = [] 数组对象的引用指向一个空数组。