新/奇怪的Java" try（）"句法？ [英] New/strange Java "try()" syntax?

问题描述

在使用Eclipse中的自定义格式选项时，在其中一个示例代码中，我看到了如下代码：

While messing around with the custom formatting options in Eclipse, in one of the sample pieces of code, I saw code as follows:

/**
 * 'try-with-resources'
 */
class Example {
    void foo() {
        try (FileReader reader1 = new FileReader("file1"); FileReader reader2 = new FileReader("file2")) {

        }
    }
}

我从未见过尝试这样使用我已经用Java编写了9年！有人知道你为什么要这样做吗？这样做有什么用例/好处？

I've never seen try used like this and I've been coding in Java for 9 years! Does any one know why you would do this? What is a possible use-case / benefit of doing this?

我看到的其他代码片段，我认为这是一个非常有用的简写，所以我在这里分享它同样，它的作用非常明显：

An other pieces of code I saw, I thought was a very useful shorthand so I'm sharing it here as well, it's pretty obvious what it does:

/**
 * 'multi-catch'
 */
class Example {
    void foo() {
        try {
        } catch (IllegalArgumentException | NullPointerException | ClassCastException e) {
            e.printStackTrace();
        }
    }
}

推荐答案

它是在Java 7中添加的。它被称为 try-with-resources 声明。

It was added in Java 7. It's called the try-with-resources statement.

/编辑

不妨把它放在这里。如果你使用这样的包装类，你可以使用try-with-resources语句来管理 Lock ：

Might as well throw this in here too. You can use the try-with-resources statement to manage Locks if you use a wrapper class like this:

public class CloseableLock implements Closeable {
    private final Lock lock;

    private CloseableLock(Lock l) {
        lock = l;
    }

    public void close() {
        lock.unlock();
    }

    public static CloseableLock lock(Lock l) {
        l.lock();
        return new CloseableLock(l);
    }
}

try(CloseableLock l = CloseableLock.lock(lock)) { // acquire the lock
    // do something
} // release the lock

但是，由于你必须为每个资源声明一个变量，这个优点是是值得商榷的。

However, since you have to declare a variable for every resource, the advantage of this is debatable.

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