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

如果你想在每个迭代中捕获Exception,或者检查哪个迭代抛出了Exception,并捕获迭代中的每个Exception,放置try…在循环内捕获。如果发生异常,这将不会中断循环,并且您可以在整个循环的每次迭代中捕获每个异常。

如果你想打破循环并在抛出异常时检查异常,请使用try…从循环中捕获。这将打破循环并在catch(如果有的话)之后执行语句。

这完全取决于你的需要。我更喜欢用try…如果Exception发生,结果不会有歧义,并且循环不会中断并完全执行。

其他回答

你应该喜欢外面的版本而不是里面的版本。这只是规则的一个特定版本,将任何可以移动到循环外的东西移动到循环外。根据IL编译器和JIT编译器的不同,您的两个版本最终可能具有不同的性能特征,也可能没有。

另一方面,你可能应该看看float。TryParse或Convert.ToFloat。

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。

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

如果这是一个全有或全无的失败,那么第一种格式是有意义的。如果希望能够处理/返回所有未失败的元素,则需要使用第二种形式。这些就是我选择方法的基本标准。就我个人而言,如果是孤注一掷,我不会使用第二种形式。

如果将try/catch放在循环中,则会在异常发生后继续循环。如果你把它放在循环之外,你会在抛出异常时立即停止。