Thread Local

If you create an object of a class that implements the Runnable interface and then start various Thread objects using the same Runnable object, all the threads share the same attributes. This means that, if you change an attribute in a thread, all the threads will be affected by this change.

Sometimes, you will be interested in having an attribute that won't be shared between all the threads that run the same object. The Java Concurrency API provides a clean mechanism called thread-local variables with a very good performance.

public class ThreadWithLocalVar implements Runnable {
    /**
     * ThreadLocal shared between the Thread objects
     */
    private static ThreadLocal<Date> startDate= new ThreadLocal<Date>() {
        protected Date initialValue(){
            return new Date();
        }
    };
    ...
}