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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)?
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NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.
CWE-476: NULL Pointer Dereference: A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.
Programmers typically catch NullPointerException under three circumstances: The program contains a null pointer dereference. Catching the resulting exception was easier than fixing the underlying problem. The program explicitly throws a NullPointerException to signal an error condition.
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).
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