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

异常的全部意义在于鼓励第一种风格:让错误处理被合并并处理一次,而不是在每个可能的错误位置立即处理。

其他回答

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。

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

为try/catch设置一个特殊的堆栈框架会增加额外的开销,但是JVM可能能够检测到您正在返回并优化它。

根据迭代次数的不同,性能差异可能可以忽略不计。

然而,我同意其他人的观点,把它放在循环之外会让循环体看起来更干净。

如果您希望继续处理,而不是在存在无效数字时退出,那么您将希望代码位于循环中。

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。

As already mentioned, the performance is the same. However, user experience isn't necessarily identical. In the first case, you'll fail fast (i.e. after the first error), however if you put the try/catch block inside the loop, you can capture all the errors that would be created for a given call to the method. When parsing an array of values from strings where you expect some formatting errors, there are definitely cases where you'd like to be able to present all the errors to the user so that they don't need to try and fix them one by one.