遍歷List的同時對List進行修改

先上代碼:

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不會拋出ConcurrentModificationException異常;但example1,example3則會拋出ConcurrentModificationException異常;

原因分析:

example1沒調用Iterator的remove方法進行刪除;在itr1.next()中會檢查

ourList.modCount != expectedModCount

則拋出ConcurrentModificationException異常;

@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循環內部其實也是使用了Iterator來遍歷Collection，它也調用了Iterator.next()，這同樣也會檢查(元素的)變化並拋出ConcurrentModificationException!