不间断切换

Switch without break(不间断切换)

问题描述

我有一些 switch 语句，如下所示.注意没有休息.Findbugs 仅在第二个 case 语句上报告错误.错误是:在一个案例落入下一个案例的地方找到了 Switch 语句.

I have some switch statement as shown below. Notice there is no break. Findbugs is reporting error on the second case statement only. The error is : Switch statement found where one case falls through to the next case.

switch(x) {

    case 0:
        // code

    case 1:
        // code

    case 2:
        // code
}

推荐答案

Findbugs 指出如果第一个有任何代码，从一个 case 跌到下一个通常不是一个好主意一个(尽管有时它可以起到很好的效果).所以当它看到第二个 case 并且没有 break 时，它会报告错误.

Findbugs is flagging up that falling through from one case to the next is generally not a good idea if there's any code in the first one (although sometimes it can be used to good effect). So when it sees the second case and no break, it reports the error.

例如:

switch (foo) {
    case 0:
        doSomething();
    case 1:
        doSomethingElse();
    default:
        doSomeOtherThing();
}

这是完全有效的 Java，但它可能没有达到作者的意图:如果 foo 是 0，所有三个doSomething、doSomethingElse 和 doSomeOtherThing 函数运行(按此顺序).如果 foo 是 1，则只有 doSomethingElse 和 doSomeOtherThing 运行.如果 foo 是任何其他值，则只有 doSomeOtherThing 运行.

This is perfectly valid Java, but it probably doesn't do what the author intended: If foo is 0, all three of the functions doSomething, doSomethingElse, and doSomeOtherThing run (in that order). If foo is 1, only doSomethingElse and doSomeOtherThing run. If foo is any other value, only doSomeOtherThing runs.

相比之下:

switch (foo) {
    case 0:
        doSomething();
        break;
    case 1:
        doSomethingElse();
        break;
    default:
        doSomeOtherThing();
        break;
}

这里只有一个函数会运行，具体取决于foo的值.

Here, only one of the functions will run, depending on the value of foo.

由于忘记 break 是一种常见的编码错误，Findbugs 等工具会为您标记出来.

Since it's a common coding error to forget the break, tools like Findbugs flag it up for you.

有一个常见的用例，你有多个 case 语句在一行中 no 介入代码:

There's a common use-case where you have multiple case statements in a row with no intervening code:

switch (foo) {
    case 0:
    case 1:
        doSomething();
        break;
    case 2:
        doSomethingElse();
        break;
    default:
        doSomeOtherThing();
        break;
}

如果 foo 是 0 or 1doSomething>.大多数工具不会将此标记为可能的编码错误，因为在 case 1 之前的 case 0 中没有代码，这是一种相当常见的模式.

There, we want to call doSomething if foo is 0 or 1. Most tools won't flag this up as a possible coding error, because there's no code in the case 0 prior to the case 1 and this is a fairly common pattern.

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