autocloseable习语上可能的空指针异常

Question

Consider the following try-with-resources block:

try (Foo foo = getAFoo()) {

}

For some class Foo that implements java.lang.AutoCloseable .

If getAFoo() were to return null , then would a null pointer exception be thrown on the closing brace (due to the runtime attempting to call close )?

Answer 1

According to this Oracle blog :

After due consideration the JSR 334 expert group has decided the semantics of the try-with-resources statement on a null resource should be changed as follows: the compiler-generated calls to close a resource will only occur if the resource is non-null.

This means that you can close any null resource in a try (with resources) block without throwing an error (and the same when the program automatically tries to close the resource when the try ends).

Answer 2

You implement java.lang.AutoCloseable , so the compiler wil try to close resource when done, but process to close a resource will only occur if the resource is non-null . So in this case I think no exception will be thrown.