There are three types of oops in java.
1.Encapsulation:Encapsulation is mechanism,that binds
together data and code its manipulates.
Ex:suppose we are writing one bean.we declaring two private
variables.we are providing setters and getters methods of
two variables.These variables are accessed in that class.
2.Inheritance:To acquire the base class properties into
derived class.
Ex:class A{
 m1(){
 System.out.println("m1 method");
 }
}
class B extends A{
 m2(){
  System.out.println("m2 method");
 }
 public static void main(String args[]){
   B b = new B();
   System.out.println(b.m1);
   System.out.println(b.m2);
 }
}
O/p is:m1 method
       m2 method.
Polymorphism:one Interface to be used for a general class of
actions.
There are two types of polymorphisms.
1.Compile-time polymorphism:what object will be assigned to
the present variable.This will be evaluated at compile time.
This is known as compile-time polymorphism.
2.Run-time polymorphism:what object will be assigned to the
present variable.This will be evaluated at runtime depending
on condition.This is known as Run-time polymorphism.