java：如何声明final在try-catch块中初始化的变量？ [英] java: how to declare final a variable that is initialized inside a try - catch block?

问题描述

我有一个变量，它不应该在初始化后改变它的值，所以我想把它定义为最终变量。

I have a variable that is not supposed to change its value after it's been initialized, so I want to define it as a final variable.

问题在于变量必须在try块内初始化，所以我遇到以下麻烦：

the problem is that the variable has to be initialized inside a try block, so I get the following troubles:

我有以下代码：

Connection conn = null;
try {
    conn = getConn(prefix);
    [...do some stuff with conn...]
} catch (Exception e) {
    throw new DbHelperException("error opening connection", e);
} finally {
    closeConnection(conn);
}

如果我将变量声明为final，而不将其初始化为null，我得到在finally块上的'局部变量conn可能尚未初始化'。另一方面，如果我将其声明为final并将其初始化为null，则会在try块中收到错误无法分配最终局部变量conn。

If I declare the variabale as final, without initializing it to null, I get a 'The local variable conn may not have been initialized' on the finally block. On the other hand, if I declare it final and initialize it to null, I get the error 'The final local variable conn cannot be assigned' in the try block.

编辑：在lxx回答后，我带来了这个版本

after lxx answer, I came with this version

try {
    final Connection conn = conn = getConn(prefix);
    try {
        return selectAll(conn, sql, params);
    } catch (Exception e) {
        throw new DbHelperException("error executing query", e);
    } finally {
        closeConnection(conn);  
    }
} catch (Exception e) {
    throw new DbHelperException("error opening connection", e);
}

所以这应该是这样做的方法吗？

So this should be the way to do it?

-

获得的经验教训：

我认为正确答案问题是lxx给出的问题，但在这种情况下，我猜是宣布变量最终的利弊超过了它的好处......

I think that the correct answer to the question is the one that lxx gave, but in this case I guess that the cons of declaring the variable final outweights it's benefits...

-

编辑：发现有关何时使用最终的堆栈溢出的两个问题

found two questions on stack overflow about when to use final

什么时候应该使用final作为方法参数和局部变量？

< a href =https://stackoverflow.com/questions/137868/using-final-modifier-whenever-applicable-in-java>使用final和final。适用于java的修饰符

推荐答案

您可以更准确地处理异常。如果你得到一个Exception打开连接，你不必在finally块中关闭它我猜。如果之后得到异常，则在try块中，并在新的嵌套try-catch块中处理异常，您不需要在外部定义变量。类似于：

You could handle the Exceptions more accurately. If you get an Exception opening the connection, you don't have to close it in the finally block I guess. If you get an exception after that, in the try block, and handle the exception in a new nested try-catch block you don't need to define the variable outside. Something like:

    try {
        final Connection conn = getConn(prefix);
        try {
            //code using conn
        } catch (Exception e) {

        } finally {
            closeConnection(conn);
        }
    } catch (DbHelperException e) {
        throw new DbHelperException("error opening connection", e);
    }

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