1)       Encapsulation:  The data members and the method are bound in a single unit and wrapped by a class. This feature of object oriented programming is called encapsulation. The data members’ visibility can be checked from being accessed outside the class.

2)       Visibility control of variables and method: . Variables and methods of a class are accessible anywhere in the program. In some situations the need of restricting the access to some variable or methods may arise. This can be controlled by visibility modifiers or “Access specifies “

3)       Visibility Modifiers / Access Modifiers:  These are the keywords that precede the declaration of variables or methods. They restrict the accessibility of the variables. Java provides fours kinds of access : public, private, protected and friendly (the default access).

               Public: It allows the variables (data members) and methods visible to all classes outside the class in which it is defined.

Syntax

               Public datatype variable name

               Public <return type> methodname();

Example

               Public int ac;

               Public void sum(int a, int b)

               {

                              int c = a + b;

                              System.out.println©;

               }

Protected: The protected variables and methods are accessible in all classes and sub-classes of the same package as well as to sub-classes in other packages.

Private: The private members are accessible only within the class in they are defined. They cannot be inherited to derived classes.

4)       Friendly Classes: When the declaration of the members is not preceded by any access modifier (the default access) then these members can be accessed in all classes within the same package.

5)       Scope of variable: Scope refers to the region where the variable van be accessed depending on the part of the program where they are declared. Depending on the scope, they are classified as instance variable, class variables and local variables.

6)       Local variables: Variables declared and used within a method are called local variables. They cannot be used outside the body of the method.

For example,

                              void sum()

{

               int a = 5,b=10,c;

               c = a + b;

               System.out.println©;

}

Here scope of a,b, and c is the method sum() so they are local variables

7)       Instance variables / Member variables: They are declared in the class body but they are not contained in any constructor or method.

For example

                              class abc

                              {

                                             int num1;

                                             double num2;

                                             abc()

                                             {

                                                            num1 = 0;

                                                            num2 = 0;

                                             }

                              }

Here num1, num2 are instance variables. They may take different values for each object of the class as whenever an  object is created, a new copy of memory location(instance variable) is created

8)       Class variables : These variables are associated with the class rather than its objects,

The values that they take  are global to the class and do not belongs to any objects they are created by precedind the variable declaration statement with the keyword static.

For ex,

                              class abc

                              {

                                             static in x , y;

                                             static void sum()

                                             {

                                                            statements;

                                             }

                              };

9)       Interface: Is is a set variables and methods like a class. The other classes may implements an interface.