Domanda di colloquio di IBM

What is Immutable class in java ? Create your own immutable class ? what is singleton and factory ? how to make singleton class thread safe? What are Demon Thread in Java ? What is Garbage collection ?What is the priority of GC ? Difference between Comparator and comparable? Questions from Hash code and equals method for Custom Objects . Difference between hashmap and hash table? what is Dependency injection ? what is beans and its life cycle ? Questions from Application COntext and annotations. Create a REST API to give the response as hello world . Different methods in REST -PUT , POST ,GET , DELETE? Difference between PUT and POST?