Access Control to Class Members

1. Access Control to Class Members • In its support for encapsulation, the class provides two major benefits. • First, it links data with the code that manipulates it. • Second, it provides the means by which access to members can be controlled. • In essence, there are two basic types of class members: public and private. • A public member can be freely accessed by code defined outside of its class. tMyn

2. A private member can be accessed only by other methods defined by its class. • It is through the use of private members that access is controlled. • Restricting access to a class’s members is a fundamental part of object-oriented programming because it helps prevent the misuse of an object. • By allowing access to private data only through a well-defined set of methods, you can prevent improper values from being assigned to that data – by performing a range check, for example. • It is not possible for code outside the class to set the value of a private member directly. tMyn

3. You can also control precisely how and when the data within an object is used. • Thus, when correctly implemented, a class creates a “black box” that can be used, but the inner workings of which are not open to tampering. • The default setting is essentially public. • Member access control is achieved through the use of three access specifiers (access modifiers): public, private, and protected. • The protected access specifier applies only when inheritance is involved and it is described later. tMyn

4. When a member of a class is modified by the public access specifier, that member can be accessed by any other code in your program wherever the program has a reference to an object of that class or one of its derived classes. • When a member of a class is specified as private, that member can be accessed only by other members of its class. Thus, methods in other classes cannot access a private member of another class. • The default access setting (in which no access specifier is used) is the same as public unless your program is broken down into packages. tMyn

5. A package is, essentially, a grouping of classes. • Packages are both an organizational and access control feature, and those topics will be discussed later. • An access specifier must begin a member’s declaration statement. tMyn

6. package TimoSoft; public class Student { private String firstName; private String lastName; public void getFirstName() { System.out.println("The first name is "+firstName+"."); } public void getLastName() { System.out.println("The last name is "+lastName+"."); } public void setFirstName(String fVal) { firstName=fVal; } tMyn

7. public void setLastName(String lVal) { lastName=lVal; } public Student(String first, String last) { setFirstName(first); setLastName(last); } } tMyn

8. Let’s modify the previous example: the instance variables will be asked from the user of the program: tMyn

9. package TimoSoft; import java.util.Scanner; public class Student { private String firstName; private String lastName; public void getFirstName() { System.out.println("The first name is "+firstName+"."); } public void getLastName() { System.out.println("The last name is "+lastName+"."); } public void setFirstName() { Scanner fromKeyboard=new Scanner(System.in); System.out.print("Enter the first name, please: "); firstName=fromKeyboard.nextLine(); } tMyn

10. public void setLastName() { Scanner fromKeyboard=new Scanner(System.in); System.out.print("Enter the last name, please: "); lastName=fromKeyboard.nextLine(); } public Student() { setFirstName(); setLastName(); } } tMyn

11. package TimoSoft; public class StudentTest { public static void main(String[] args) { Student first=new Student(); first.getFirstName(); first.getLastName(); } } run: Enter the first name, please: Susan "YouTube" Enter the last name, please: Boyle The first name is Susan "YouTube". The last name is Boyle. BUILD SUCCESSFUL (total time: 23 seconds) tMyn