deployer is responsible for the following security-related tasks:
Mapping the application permission model provided by the application assembler to policies and mechanisms specific to the operational environment.

Assigning principals to the security roles in the deployment descriptor.
A deployer receives the packaged files and deployment descriptor from the application assembler. The assembler assigns a logical name to the security role, which may not be used in the real environment. The deployer matches this logical name to the real user.

The getCallerIdentity() method is used to obtain the java.security.Identity of the caller. The container is allowed to return null from this method. The enterprise bean should use the getCallerPrincipal method instead. The following is the general form of the method:

public java.security.Identity getCallerIdentity()

This method returns the Identity object that identifies the caller.

HTTP 1.1 defines eight request methods as follows:

Each of the above XXX request methods (except CONNECT) has a corresponding doXXX method in the HttpServlet class.

The createNewFile() method of the File class is used to create a new empty file if a file with the given name does not already exist. It returns true if a file with the given name does not exist and is successfully created; otherwise, it returns false.

getTime(): The getTime() method returns a date/time of the calendar in a Date object. Date objects are stored as an offset in milliseconds. The general form of the getTime() method is as follows:

Date getTime()

e.g. System.out.println(calendar.getTime());

setTime(): The setTime() method sets the current calendar’s date/time from the value of the specified date. The general form of the setTime() method is as follows:

void setTime(Date date)

e.g. calendar.setTime(date2);

The readLine() method belongs to the Console class. This method is used to read a line of text from the console. There are two syntaxes of the readLine() method as follows:

readLine(): This method is used to read a line of text from the console. It returns a null value if an end of stream has been reached.

public String readLine(String fmt, Object… args): This method provides a formatted prompt and then reads a line of text from the console. It returns a null value if an end of stream has been reached.

abstract class Ques0347A{
int x;
int init(){
x = 15;
return x;
}
abstract void disp();
}

public class Ques0347 extends Ques0347A{
void disp(){
int y = init();
System.out.println(y);
}
public static void main(String[] argv) {
Ques0347 ob = new Ques0347();
ob.disp();
}
}

An abstract class can be inherited as same as a simple class by using the extends clause. In the given code, there are two classes named Ques0347A and Ques0347. The Ques0347A class is declared as abstract because it contains a declaration of an abstract method named disp. It also contains an instance variable x and an instance method init().

The extends clause in the declaration of the Ques0347 class suggests that it is a subclass of the abstract class Ques0347A. As the Ques0347 class provides an implementation of the disp() method, it is not declared as abstract. Ques0347 being a subclass of the Ques0347A class inherits the init() method and the variable x.

Hence, it is necessary of we inherit an abstract class then the sublcass will implement all the methods that are left unimplemented in the superclass.