在Java中，当catch块和finally块都抛出异常时会发生什么?

Question

考虑一下我在面试中被问到的这个问题

public class Test_finally {
    private static int run(int input) {
        int result = 0;
        try { 
            result = 3 / input;
        } catch (Exception e) {
            System.out.println("UnsupportedOperationException");
            throw new UnsupportedOperationException("first");
        } finally {
            System.out.println("finally input=" + input);
            if (0 == input) {
                System.out.println("ArithmeticException");
                throw new ArithmeticException("second");
            }
        }
        System.out.println("end of method");
        return result * 2;
    }
    public static void main(String[] args) {
        int output = Test_finally.run(0);
        System.out.println("  output=" + output);
    }
}

此程序的输出抛出ArithmeticException而不是UnsupportedOperationException

面试官只是问我如何让客户知道最初提出的异常类型是UnsupportedOperationException而不是ArithmeticException。我不知道

Answer 1

永远不要返回或抛出finally块。作为一个面试官，我希望得到这样的答案。

一个蹩脚的面试官在寻找一个小的技术细节时可能会期望你知道Exception.addSuppressed()。你实际上不能在finally块中读取抛出的异常，所以你需要将它存储在throw块中以重用它。

就像这样:

private static int run(int input) throws Exception {
    int result = 0;
    Exception thrownException = null;
    try {
        result = 3 / input;
    } catch (Exception e) {
        System.out.println("UnsupportedOperationException");
        thrownException = new UnsupportedOperationException("first");
        throw thrownException;
    } finally {
        try {
            System.out.println("finally input=" + input);
            if (0 == input) {
                System.out.println("ArithmeticException");
                throw new ArithmeticException("second");
            }
        } catch (Exception e) {
            // Depending on what the more important exception is,
            // you could also suppress thrownException and always throw e
            if (thrownException != null){
                thrownException.addSuppressed(e);
            } else {
                throw e;
            }
        }
    }
    System.out.println("end of method");
    return result * 2;
}