ThreadLocal versus Member Variable in a Thread in Java

Question

Can we get back reference to a member variable of a Thread like the way we get for ThreadLocal?

For example, lets say we use a counter variable to counter amount of requests processed by the Thread in a ThreadLocal variable. Consider that we are using a ThreadPool Executer for reusing threads. Now every Thread keeps a reference to a ThreadLocal counter variable and it can increment its own copy after every request. In a similar manner if i have a Member variable inside a Runnable, can i get back a reference to it? The Thread is anyway being reused.

Answer 1

if i have a Member variable inside a Runnable, can i get back a reference to it?

When you say "a Runnable", you're talking about some object that implements the Runnable interface. There is nothing magic about Runnable and there is nothing magic about a run() method.

The member variables of your Runnable object are just like the member variables of any other object, and your code accesses them in the same way.

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P.S., Usually, when you see ThreadLocal in a program, it means

• The program used to be single-threaded,
• It keeps a lot of its state in static variables,
• Somebody added multi-threading as an after-thought, and
• It makes sense for some of that static state to be duplicated for each thread.

I would almost never use ThreadLocal in a new program, because I try hard not to write any code that depends on static variables, and if you're using ThreadLocal for non-static data, you're probably making your program way more complicated than it needs to be.