应该……接住环内还是环外?

我有一个这样的循环:

for (int i = 0; i < max; i++) {
    String myString = ...;
    float myNum = Float.parseFloat(myString);
    myFloats[i] = myNum;
}

这是一个方法的主要内容，该方法的唯一目的是返回浮点数数组。我想让这个方法在出现错误时返回null，所以我把循环放在try…Catch block，像这样:

try {
    for (int i = 0; i < max; i++) {
        String myString = ...;
        float myNum = Float.parseFloat(myString);
        myFloats[i] = myNum;
    }
} catch (NumberFormatException ex) {
    return null;
}

但后来我也想到试一试……Catch块在循环中，像这样:

for (int i = 0; i < max; i++) {
    String myString = ...;
    try {
        float myNum = Float.parseFloat(myString);
    } catch (NumberFormatException ex) {
        return null;
    }
    myFloats[i] = myNum;
}

是否有任何理由，性能或其他方面，更喜欢其中一个?

编辑:共识似乎是，将循环放在try/catch中更干净，可能是在它自己的方法中。然而，关于哪个速度更快仍存在争议。有人能测试一下并给出一个统一的答案吗?

当前回答

上面没有提到的另一个方面是，每个try-catch都会对堆栈产生一些影响，这可能会对递归方法产生影响。

如果方法"outer()"调用方法"inner()"(它可能递归地调用自己)，如果可能的话，尝试在方法"outer()"中找到try-catch。我们在性能类中使用的一个简单的“堆栈崩溃”示例，当try-catch在内部方法中时，在大约6400帧时失败，当它在外部方法中时，在大约11,600帧时失败。

在现实世界中，如果您正在使用Composite模式并且具有大型、复杂的嵌套结构，这可能会成为一个问题。

2010-03-11 19:06:16

其他回答

性能:

try/catch结构放置的位置绝对没有性能差异。在内部，它们被实现为调用方法时创建的结构中的代码范围表。当方法执行时，try/catch结构完全不在图中，除非发生抛出，然后将错误的位置与表进行比较。

这里有一个参考:http://www.javaworld.com/javaworld/jw-01-1997/jw-01-hood.html

这张桌子在一半的地方被描述。

2008-09-26 20:09:17

在你的例子中没有功能上的区别。我觉得你的第一个例子可读性更强。

2008-09-26 19:55:34

我想添加我自己的0.02c，关于在哪里放置异常处理的一般问题时两个相互竞争的考虑因素:

The "wider" the responsibility of the try-catch block (i.e. outside the loop in your case) means that when changing the code at some later point, you may mistakenly add a line which is handled by your existing catch block; possibly unintentionally. In your case, this is less likely because you are explicitly catching a NumberFormatException The "narrower" the responsibility of the try-catch block, the more difficult refactoring becomes. Particularly when (as in your case) you are executing a "non-local" instruction from within the catch block (the return null statement).

2008-10-05 15:41:53

My perspective would be try/catch blocks are necessary to insure proper exception handling, but creating such blocks has performance implications. Since, Loops contain intensive repetitive computations, it is not recommended to put try/catch blocks inside loops. Additionally, it seems where this condition occurs, it is often "Exception" or "RuntimeException" which is caught. RuntimeException being caught in code should be avoided. Again, if if you work in a big company it's essential to log that exception properly, or stop runtime exception to happen. Whole point of this description is PLEASE AVOID USING TRY-CATCH BLOCKS IN LOOPS

2019-02-13 21:56:01

As long as you are aware of what you need to accomplish in the loop you could put the try catch outside the loop. But it is important to understand that the loop will then end as soon as the exception occurs and that may not always be what you want. This is actually a very common error in Java based software. People need to process a number of items, such as emptying a queue, and falsely rely on an outer try/catch statement handling all possible exceptions. They could also be handling only a specific exception inside the loop and not expect any other exception to occur. Then if an exception occurs that is not handled inside the loop then the loop will be "preemted", it ends possibly prematurely and the outer catch statement handles the exception.

如果循环在生活中扮演清空队列的角色，那么循环很可能在队列真正清空之前就结束了。非常常见的错误。

2012-08-31 09:08:33

应该……接住环内还是环外?

推荐文章

最新文章

标签