couldn't use lambda expression to create the ThreadLocal class

Question

I have the below code

      ThreadLocal<Map<String, Service<Request, Response>>> connectinonMapThread = new ThreadLocal<Map<String, Service<Request, Response>>>() {
        @Override
        protected Map<String, Service<Request, Response>> initialValue() {
            return new HashMap<String, Service<Request, Response>>();
        }
    };

I want to write it using lambda expression like below -

ThreadLocal<Map<String, Service<Request, Response>>> connectinonMapThread2 = new ThreadLocal<Map<String, Service<Request, Response>>>(() -> new HashMap<String, Service<Request, Response>>());

I tried another one.

ThreadLocal<Map<String, Service<Request, Response>>> connectinonMapThread2 = initialValue() -> {

            return new HashMap<String, Service<Request, Response>>();
    };

But I am getting compilation error. But the IntelliJ Idea suggests this could be written as lambda expression.

The [diamond operator](https://www.baeldung.com/java-diamond-operator) has been in Java for 4 years. Please use it. — Michael, Oct 16 '18 at 15:49
There is no such constructor. Use `withInitial(Supplier)` and provide the lambda there. — Sotirios Delimanolis, Oct 16 '18 at 15:50
`ThreadLocal>> connectionMapThread = ThreadLocal.withInitial(HashMap::new);` — Holger, Oct 16 '18 at 15:52

score 5 · Accepted Answer · answered Oct 16 '18 at 15:51

ThreadLocal<Map<String, Service<Request, Response>>> test = 
            ThreadLocal.withInitial(HashMap::new);

You are trying to assign a lambda expression to a non-functional interface, this will not work. Fortunately ThreadLocal offers one option with a Supplier via withInitial method

couldn't use lambda expression to create the ThreadLocal class

1 Answers1