When and how should I use a ThreadLocal variable?

Question

When should I use a ThreadLocal variable?

How is it used?

Answer 1

There are 3 scenarios for using a class helper like SimpleDateFormat in multithread code, which best one is use ThreadLocal

Scenarios

1- Using like share object by the help of lock or synchronization mechanism which makes the app slow

2- Using as a local object inside a method

In this scenario, if we have 4 thread each one calls a method 1000 time then we have
4000 SimpleDateFormat object created and waiting for GC to erase them

3- Using ThreadLocal

if we have 4 thread and we gave to each thread one SimpleDateFormat instance
so we have 4 threads, 4 objects of SimpleDateFormat.

There is no need of lock mechanism and object creation and destruction. (Good time complexity and space complexity)