编译器如何理解下面运行的异常？

Question

    try {
        Image image = new Image("MyComputer/Documents/Photos/estambul.jpg");

        try {
            //...

            image.print();

            throw new NullPointerException();
        } finally {
            System.out.println("FINALLY");
            image.close();
            throw new IOException();
        }
    } catch (IOException ex){
        System.out.println("IO_EXCEPTION");
        System.out.println(ex.getMessage());
    }

    System.out.println("THREAD IS CONTINUE");

这里没有抛出NullPointerException。但是，没有捕获它的 catch 块。看起来 IOException 正在压缩 NullPointerException。你的评论是什么？没看懂。

Answer 1

NullPointerException is not thrown here.

实际上，它是...假设代码到达了您明确抛出它的语句。

但问题是内部 try 有一个 finally 块。在 finally 块中，您明确抛出了一个 IOException。这将取代原来的异常。

行为在 JLS 14.20.2 中指定。管理您示例的文本是：

"If execution of the try block completes abruptly because of a throw of a value V, then there is a choice:

...

If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and the throw of value V is discarded and forgotten)."

It looks like IOException is squashing NullPointerException.

有点。但是，我们使用非正式术语 squashing 来指代捕获和忽略异常的做法。

Then it can only handle one exception at runtime.

没错。在任何时间点，每个线程最多只能有一个“突然终止原因”。

编译器如何理解下面运行的异常？

How does the compiler understand which exception to run below?

java

exception

try-catch

try-catch-finally

编译器如何理解下面 运行 的异常？

How does the compiler understand which exception to run below?

java

exception

try-catch

try-catch-finally

编译器如何理解下面运行的异常？