Java Predicate implementation can't access global final variable

Question

I created a simple rest service using java, and springboot. here is my service layer code

@Service
class MyService {
    private final TestService service;

    @Autowired
    public MyService(final TestService service) {
        this.service = service;
    }

    // here is the issue
    private final Predicate<User> userPredicate = (user) -> this.service.isValidUser(user);
}

In the above line, the ide complaining about the variable service might not be initialized, and I can not use it in the predicate implementation. I tried removing final to the service, that works, but I do not want to remove final to the TestService declaration.

Anyone have any solution ?

Is it just your IDE? Do you get the same error from the command line? — markspace, Jan 11 '22 at 00:24
There are no global variables in Java, and `service` is not an exception to this. — user207421, Feb 10 '22 at 03:21

score 6 · Accepted Answer · answered Jan 11 '22 at 00:24

Execution order is: First all initializing expressions are resolved in lexical order (top to bottom through the file), then the constructor runs.

In other words, that userPredicate = line runs before your this.service = service; line. It's doomed to failure, and the compiler knows it, so it will refuse to compile this code.

The fix is trivial - move that userPredicate initialization into the constructor:

private final TestService service;
private final Predicate<User> userPredicate;

@AutoWired
public MyService(TestService service) {
  this.service = service;
  this.userPredicate = user -> service.isValidUser(user);
}

For what its worth, if you don't need the service for anything except making that userPredicate, might as well get rid of the service field entirely.

Java Predicate implementation can't access global final variable

1 Answers1