Can constructer be synchronized

Whether set allows null

Difference between Application server and web server

Can constructors be synchronized in Java

What is IOC.

Inversion of Control or Dependency Injection means passing on the control to Spring container.
In IOC, the objects are not created in code but it is described in a configuration file, how the objects are to be created. the container takes the responsibilty

Inner Classes

Anonymous Inner Class
Static Inner Class
Inner Class

Collections Interview Questions

IdentityHashMap
CopyOnWriteArrayList
ConcurrentHashMap