遍历List的同时对List进行修改

来源：互联网发布：什么是java反射机制编辑：程序博客网时间：2024/06/08 16:24

先上代码:

Collection<String> list = new ArrayList<String>();        list.add("Android");        list.add("iPhone");        list.add("Windows Mobile");         // example 0        Iterator<String> itr0 = list.iterator();        while(itr0.hasNext()){            String lang = itr0.next();            itr0.remove();        }                // example 1                Iterator<String> itr1 = list.iterator();        while(itr1.hasNext()){            String lang = itr1.next();            list.remove(lang);        }         // example 2        for(int i = 0; i < list.size(); i++){            list.remove(i);        }                // example 3        for(String language: list){            list.remove(language);        }

example0,example2不会抛出ConcurrentModificationException异常;但example1,example3则会抛出ConcurrentModificationException异常;

原因分析:

example1没调用Iterator的remove方法进行删除;在itr1.next()中会检查

ourList.modCount != expectedModCount

则抛出ConcurrentModificationException异常;

@SuppressWarnings("unchecked") public E next() {            ArrayList<E> ourList = ArrayList.this;            int rem = remaining;            if (ourList.modCount != expectedModCount) {                throw new ConcurrentModificationException();            }            if (rem == 0) {                throw new NoSuchElementException();            }            remaining = rem - 1;            return (E) ourList.array[removalIndex = ourList.size - rem];        }

example3的for-each循环内部其实也是使用了Iterator来遍历Collection，它也调用了Iterator.next()，这同样也会检查(元素的)变化并抛出ConcurrentModificationException!

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