Java try-finally返回设计问题

问题描述

在Java中，尝试{...}最终{...}对我来说有些不直观。如另一个问题所示，，如果你在try块中有一个return语句，如果定义了finally块，它将被忽略。例如，函数

  boolean test（）{
 try {
 return true; 
} 
最后{
返回false; 
} 
} 
  

将始终返回false。我的问题：这是为什么？这个由Java制定的设计决策背后有一个特定的哲学吗？感谢任何见解，谢谢。

编辑：我特别感兴趣的是'为什么'Java认为可以违反我定义的语义。如果我在try块中'返回'，那么该方法应该在那里返回。但是JVM决定忽略我的指令并从实际上还没有 到达的子程序返回。

解决方案

从技术上讲，如果 finally 块为 return em>已定义，仅当finally块还包含 return 。

这是一个可疑的设计回想起来可能错误的决定（很像默认情况下引用是可空的/可变的，并且根据一些情况，检查异常）。在许多方面，这种行为与对最终的含义的口语理解完全一致 - 无论事先在中发生什么，请尝试阻止，始终运行此代码。因此，如果从 finally 块返回true ，整体效果必须始终为true，不是吗？ / p>

一般来说，这很少是一个很好的习惯用法，你应该使用 finally 块来清理/关闭资源但很少从它们那里返回一个值。

In Java, a try { ... } finally { ... } is executed somewhat unintuitively to me. As illustrated in another question, Does finally always execute in Java?, if you have a return statement in the try block, it will be ignored if a finally block is defined. For example, the function

boolean test () {
    try {
        return true;
    }
    finally {
        return false;
    }
}

will always return false. My question: why is this? Is there a particular philosophy behind this design decision made by Java? I appreciate any insight, thank you.

Edit: I'm particularly interested as to 'why' Java thinks it's ok to violate the semantics that I define. If I 'return' in a try block, the method should return right then and there. But the JVM decides to ignore my instruction and return from a subroutine that actually hasn't yet been reached.

解决方案

Technically speaking, the return in the try block won't be ignored if a finally block is defined, only if that finally block also includes a return.

It's a dubious design decision that was probably a mistake in retrospect (much like references being nullable/mutable by default, and, according to some, checked exceptions). In many ways this behaviour is exactly consistent with the colloquial understanding of what finally means - "no matter what happens beforehand in the try block, always run this code." Hence if you return true from a finally block, the overall effect must always to be to return true, no?

In general, this is seldom a good idiom, and you should use finally blocks liberally for cleaning up/closing resources but rarely if ever return a value from them.

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