Java做一会儿，一会儿 [英] Java do while, while

问题描述

运行此代码时可以期待什么行为:

what behaviour can I expect when I run this code:

do while(testA) {

    // do stuff

} while(testB);

它将表现为:

do {
    while(testA) {
        // do stuff
    }    
} while(testB);

或者:

if(testA) {
    do {
        // do stuff
    } while(testA && testB);
}

还是完全出乎意料的事情?

Or something totally unexpected?

我之所以问这个问题，是因为我认为这很模棱两可，对于其他正在搜索此主题的人来说，不是，因为我懒于对其进行测试.

I ask this question because I think this is quite ambiguous, and for other people searching on this topic, not because I am lazy to test it out.

推荐答案

它等效于您的第一个块:

It is equivalent to your first block:

do {
    while(testA) {
        // do stuff
    }    
} while(testB);

Java语法解析时为:

DoStatement:
    do Statement while ( Expression ) ;

Statement:
    WhileStatement

WhileStatement:
    while ( Expression ) Statement

Statement:
    Block

Block:
    { BlockStatements_opt }

您可以看到Java编译器会将其解析为do <WhileStatement> while ( Expression ) ;.这是解析您编写的代码的唯一有效方法.

You can see that the Java compiler will parse this as do <WhileStatement> while ( Expression ) ;. That's the only valid way to parse the code that you wrote.

请记住，解析此构造没有任何特殊规则.由于do-while循环的编写方式不寻常，这最终使人难以理解.在正常使用情况下，do-while总是写为do { ... } while并带有大括号.

Keep in mind that it doesn't have any special rule to parse this construct. It just ends up being confusing for a human to read due to the unusual way the do-while loop is written. In normal usage do-while is always written as do { ... } while with explicit curly braces.

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