Software Construction Series（1）

Java在循环中删除list中元素的方法

先说几个通常的错误：

1、for循环遍历list

    for (int i = 0; i < list.size(); i++) {
         if (list.get(i).equals("del"))
             list.remove(i);
    }

2、for each循环

        for (String x : list) {
            if (x.equals("del"))
                list.remove(x);
        }

错误原因：

​ 没有考虑到remove方法的实现机制。

​ 在Javadoc中，明确指出list.remove()方法的实现机制是：删除索引所指向元素，并把其后的所有元素索引-1.

remove
E remove(int index)

Removes the element at the specified position in this list (optional operation). Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the list.
Parameters:index - the index of the element to be removedReturns:the element previously at the specified positionThrows:UnsupportedOperationException - if the remove operation is not supported by this listIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())

下面的方法是正确的：

    Iterator<String> iter = list.iterator();
    while(iter.hasNext()){
        String x = iter.next();
        if(x.equals("del")){
            iter.remove();
        }
    }

可以查看Iterator的remove方法的Spec， 其中明确提到在迭代中修改list必须使用此方法。

     * Removes from the underlying collection the last element returned
     * by this iterator (optional operation).  This method can be called
     * only once per call to {@link #next}.  The behavior of an iterator
     * is unspecified if the underlying collection is modified while the
     * iteration is in progress in any way other than by calling this
     * method.