在 Java 的 foreach 循环中调用 remove [英] Calling remove in foreach loop in Java

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本文介绍了在 Java 的 foreach 循环中调用 remove的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

在 Java 中,在使用 foreach 循环遍历集合时对集合调用 remove 是否合法?例如:

List姓名 = ....对于(字符串名称:名称){//做点什么名称.删除(名称).}

作为附录,删除尚未迭代的项目是否合法?例如,

//假设姓名列表为重复条目列表<字符串>姓名 = ....对于(字符串名称:名称){//做点什么while (names.remove(name));}

解决方案

要在迭代时安全地从集合中删除,您应该使用迭代器.

例如:

List姓名 = ....迭代器<字符串>i = names.iterator();而 (i.hasNext()) {字符串 s = i.next();//必须先调用,然后才能调用 i.remove()//做点什么i.remove();}

来自 Java 文档:

<块引用>

该类的迭代器和listIterator返回的迭代器方法是快速失败的:如果列表在任何时候在结构上被修改迭代器创建后的时间,以任何方式,除了通过迭代器自己的 remove 或 add 方法,迭代器会抛出一个并发修改异常.因此,面对并发修改,迭代器快速而干净地失败,而不是在不确定的时间冒着任意的、不确定的行为的风险未来.

也许许多新手不清楚的是,使用 for/foreach 构造迭代列表会隐式地创建一个必然无法访问的迭代器.可以在此处

In Java, is it legal to call remove on a collection when iterating through the collection using a foreach loop? For instance:

List<String> names = ....
for (String name : names) {
   // Do something
   names.remove(name).
}

As an addendum, is it legal to remove items that have not been iterated over yet? For instance,

//Assume that the names list as duplicate entries
List<String> names = ....
for (String name : names) {
    // Do something
    while (names.remove(name));
}

解决方案

To safely remove from a collection while iterating over it you should use an Iterator.

For example:

List<String> names = ....
Iterator<String> i = names.iterator();
while (i.hasNext()) {
   String s = i.next(); // must be called before you can call i.remove()
   // Do something
   i.remove();
}

From the Java Documentation :

The iterators returned by this class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Perhaps what is unclear to many novices is the fact that iterating over a list using the for/foreach constructs implicitly creates an iterator which is necessarily inaccessible. This info can be found here

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