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

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.

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。

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。

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。

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.

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。