The document discusses access protection and access modifiers in Java. It explains the different access modifiers - public, private, and protected. Public members are accessible everywhere, private members are only accessible within their own class, and protected members are accessible within the class, subclasses, and packages. It provides examples of how to use access modifiers with classes and class members, and recommends generally making data private and accessor methods public. A sample Person class is provided to demonstrate applying access modifiers.

1. Objectives
On completion of this period, you would be
able to learn
• Access protection
• Access modifiers
• Applying access protection
1

2. Recap
Packages
• Name provide to a group of classes
• A collection of related classes and interfaces
• A name space management tool provided by
Java
2

3. Access Protection
• What is access protection
• In objects, certain members have to be
protected from unauthorized access
• In C++, we learnt how to do such
protection
• We used private, public, and protected
keywords for this purpose
• Java also has such features
3

4. Access Protection
• Access Protection
• To protect the access of members of an
object
• Done with the help of access modifiers
• Keywords are – private, public and
protected
• Access modifiers are also known as
Visibility Modifiers
4

5. Access Protection
• Purpose of Access Protection
• Enforces
• information hiding
• encapsulation
5

6. Access Modifiers
• Types of Access Modifiers
• public
• private
• protected
• default (no special keyword)
6

7. Access Modifiers Contd..
• public access
• Member is visible or accessible to the world
• Any method of any object can use a public
member
• keyword : public
• eg. : public int number;
• public void sum(){
• … Put before
return type
• }
• Generally access methods are public
7

8. Access Modifiers Contd..
• private access
• Member is visible or accessible only within its
own class
• Members cannot be inherited by subclasses
• Members cannot be accessible in subclasses
• Keyword : private
8

9. Access Modifiers Contd..
• private access
• eg. : private double average;
• private void debug (String msg) {
• …
• }
• Provides the highest degree of protection
9

10. Access Modifiers Contd..
• protected access
• Member is visible or accessible to
• The current class
• Subclasses of the current class
• All classes that are in the same package as
that of the class
• Keyword : protected
• eg. : protected String message Str;
• The level of protection is between public
access and default access
10

11. Access Modifiers Contd..
• default access or package access
• Members are accessible to
• All the classes in the same package
• No special keyword is used
eg. : int length;
11

12. Access Modifiers Contd..
Table 27.1: Class Member Accessibility
12

13. Rules of thumb
• public : if the member to be visible
everywhere
• protected : if the member is visible in the
current package and also subclasses in
other packages
• default : if the member to be visible in the
current package
• private : if the member is to be used only
within the class
13

14. Example
• Consider the access modifier
for a member x in class A. If it
is:
• private – it can only be
used inside A.
• default – it can be used
anywhere in package1,
that is, A,B and C.
• protected – it can be used
anywhere in package1,
and in subclasses of A in
other packages, here S.
• public – it can be used
everywhere in the system 14
Fig. 27.1. Packages with its classes

15. Example Contd..
• Consider the access
modifier for the class
B. If it is:
• default – the class
can only be used in
package1.
• public – the class
can be used from
anywhere.
Fig. 27.2. Packages with its classes
15

16. Using Access Modifiers
• Guidelines :
• Make all data members private
• Create public getter and setter methods for data
members as necessary
• If possible, make a method private, else make it
default, or make it public
16

17. Example Program
• With the help of the following program, we
will try to analyze the access protection
features
17

18. Example Program
• Consider the Person class
• What access modifiers should be used, and
which access should define?
18

19. Example Program
public class Person {
int SSNumber;
String name;
String address;
}
19

20. Example Program Contd..
public class Person {
private final int SSNumber;
private String name;
private String address;
public Person(int ssn, String name) {
SSNumber = ssn;
this. name = name;
}
public String getName() {
return name;
}
20

21. Example Program Contd..
public String getAddress () {
return address;
}
public void setAddress (String address) {
this. address = address;
}
}
21

22. • The analysis is as follows
Example Program Contd..
• The SSNumber* must be given when the person object
is created, and cannot be changed later
• The Name must be given when the object is created
Normally it will not change later
• The address need not be present, but it can be changed
along the way
22

23. Summary
• In this class we have discussed
• Access protection
• Access modifiers
• public, private, protected
• How to use access modifiers
23

24. Frequently Asked Questions
1. List the access modifiers in Java ?
2. What is the difference between default and
protected modifiers ?
3. Explain how to use access modifiers
24

25. Quiz
1. We would like to make a member of a class
visible In all subclasses regardless of what
package they are in. Which keyword is useful
for that ?
1. private
2. public
3. protected
4. No keyword (default)
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26. Quiz Contd..
2. Which keyword can make a class visible
within a package?
• private
• public
• protected
• No keyword (default)
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27. Quiz Contd..
3. Which keyword is useful for implementing
information hiding principle?
1. private
2. public
3. protected
4. No keyword (default)
CM604.27 27

28. Quiz Contd..
4. Which one of the following is NOT a keyword
related to Access protection?
1. private
2. public
3. protected
4. default
CM604.27 28