不停地切换 [英] Switch without break

问题描述

我有一些 switch 语句，如下所示.注意没有中断.Findbugs 仅在第二个 case 语句中报告错误.错误是 : Switch 语句发现一个案例落入下一个案例.

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，如果第一个中有任何代码，从一个 case 到下一个失败通常不是一个好主意一个(虽然有时候用起来效果不错).因此，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，但它可能不符合作者的意图:如果 foo 是 0，所有三个函数 doSomething、doSomethingElse 和 doSomeOtherThing 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.

相反:

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

这里只运行一个函数，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.

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，您有多个 case 语句在一行中，没有 中间代码:

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;
}

在那里，如果 foo 是 0 或 1，我们想调用 doSomething>.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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