How to use ThreadLocal variable

Question

Can someone tell me how and when should I use a ThreadLocal variable?

Answer 1

You can use a ThreadLocal variable when you have some object that is not thread-safe, but you want to avoid synchronizing access to that object. So, in that case, you can give each thread its own instance of the object.

For example:

public class Demo
{
    private static final ThreadLocal<SimpleDateFormat> formatter = new ThreadLocal<SimpleDateFormat>(){
        @Override
        protected SimpleDateFormat initialValue()
        {
            return new SimpleDateFormat("yyyyMMdd HHmm");
        }
    };

    public String formatIt(Date date)
    {
        return formatter.get().format(date);
    }
}