1. objects
a. polymorphism
b. inheritance
c. encapsulation
d. abstraction
2. strings
a. string equality
b. immutable
3. exception handling.
a. throwable
b. exceptions and errors
c. checked exceptions
d. overriding exceptions
4. threads
a. wait,notify,notifyall
b. Ready state
c. synchronization
d. sleep
e. interrupt exception
Collections
