java - autocloseable idiom 可能出现空指针异常

Question

考虑以下 try-with-resources block :

try (Foo foo = getAFoo()) {

}

对于某些实现了 java.lang.AutoCloseable 的类 Foo。

如果 getAFoo() 返回 null，那么会在右大括号上抛出空指针异常(由于运行时试图调用 close )?

Answer 1

根据 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.

这意味着您可以关闭 try(带资源) block 中的任何 null 资源而不会抛出错误(当程序自动尝试关闭try 结束时的资源)。