java - 什么是先到的 - finally 还是 catch block ？

Question

考虑以下测试用例:

public class Main {

    static int a = 0;

    public static void main(String[] args) {
        try {
            test();
            System.out.println("---");
            test2();
        }
        catch(Exception e) {
            System.out.println(a + ": outer catch");
            a++;
        }
    }

    public static void test()
    {
        try {
            throw new Exception();
        }
        catch (Exception e) {
            System.out.println(a + ": inner catch");
            a++;
        }
        finally {
            System.out.println(a + ": finally");
            a++;
        }
    }

    public static void test2() throws Exception
    {
        try {
            throw new Exception();
        }
        finally {
            System.out.println(a + ": finally");
            a++;
        }
    }
}

有输出:

0: inner catch
1: finally
---
2: finally
3: outer catch

为什么在 test() 中 catch 发生在 finally 而在 test2() 中却相反？

Answer 1

关键点如下:

• 在 try-(catch)-finally 中 block ，finally对于那个特定的try block 最后执行
• 你可以嵌套 try block 内的 block ，每个嵌套 try block 可以有自己的finally ，这将为那些个人 try 最后执行 block

是的，finally最后执行，但仅用于 try阻止它附加到。

所以给出以下代码段:

try {
    try {
        throw null;
    } finally {
        System.out.println("Finally (inner)");
    }
} catch (Throwable e) {
    System.out.println("Catch (outer)");
}

这会打印(as seen on ideone.com):

Finally (inner)
Catch (outer)

注意:

• (inner)内, Finally是最后一个(无论 catch 是否成功)
• Catch (outer)关注 Finally (inner) , 但那是因为 Finally (inner)嵌套在另一个中try阻止 (outer)

同样，以下代码段:

    try {
        try {
            throw null;
        } catch (Throwable e) {
            System.out.println("Catch (inner)");
        } finally {
            System.out.println("Finally (inner)");
            throw null;
        }
    } catch (Throwable e) {
        System.out.println("Catch (outer)");
    }

这会打印(as seen on ideone.com):

Catch (inner)
Finally (inner)
Catch (outer)

---

引用文献

• JLS 14.20.2 Execution of try-catch-finally

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