ENCAPSULATION /
CONSTRUCTOR
Ques 1 What are
instance variable?[2008]
Variable defined in a class are called instance variables.
Ques 2:-What is scope
and life time of variables?
Scope of a variable defines the section of source code from
where the variable can be accesses. As a general rule. Variable declared inside
a scope is not visible to code that is defined outside the scope, thus when you
declare a variable with in a scope, you are localizing the variable and
protecting it from unauthorized access. The life time of a variable describes
how long the variable continues to exist before it is destroyed.
Ques 3 What are
access specifiers of an interface?
In java, you can use access specifiers to protect both a class
variables and methods while declaring them. i.e. they defines which function or
method can make use of a particular method of data. The java language supports
four type of access. That are private, public, protected and default
Ques 4 Define role of
each type of access specifier
OR [2008]
Explain any two types of access specifiers.
private :- the
variable/method defined as private can be access by member method of the same
class. [2006]
protected :- the
variable/method defined as protected can
be access by member method of the same class and its derived class.
public:- the
variable/method defined as public can be
access by member method of the any
class.
Default/ friendly
:- when no access specifier is defined then it assumes default access , the
variable/method can be accessed from other class of the same package.
Ques 5:- What is the
difference between local and instance variable?
The field or variables defined within a class are called
instance variables because each instance of the class(object) contains its own
copy of these variable. The scope of an instance variable is the whole class
definition.
Where as local variable can be used only in the given method
of that particular class in which they are declared.
Ques 6: Define
constructor. what is its need.?
A constructor is a
member function of a class with the same name as that of its class name. it is
defined like other member function of a class. It is used to initialize the
data member.
The constructor is needed to initialize the object member in
the memory.
Ques 7 What is
default constructor?[2006]
Method having same name as class name, used to initialize
value when no arguments are pass to it.
Ques 8: What is a
parameterized constructor? How is it useful?
Constructor that can take argument are called parameterized
constructor. It initializes the data members based on the argument passed to
it.
Ques 9: List some
special properties of constructor.
i.
Constructor should be declared in the public section of
the class
ii.
They are invoked automatically when an object of the
class is created.
iii.
They do no have any return and cannot return any value.
iv.
Like other function they can accept parameters
v.
Default constructor do not accept parameter.
vi.
If no constructor is present then the compiler provides
a default constructor.
Ques 10: Differentiate
between constructor and method [2005]
|
Constructor
|
Method
|
|
Class name and constructor name should be same
|
Method can have any name following identifier naming rule
|
|
It is used only for initializing data member
|
Can do any type of calculation or printing.
|
|
It is not return type
|
It has return type
|
|
It is called automatically
|
It has to be called
|
Ques 11:Explain
constructor overloading with example
When two or more constructor with different function signature
is defined in a class then it is called constructor overloading.
Class overload
{
int a,b;
overload()
{
a=10;
b=20;
}
overload(int x, int y)
{
a=x;
b=y;
}}
Ques 12. What are
static data members.
Ans:- A static member si a global variable of a class. Such
data members are globally available for all the object of the class type. The
static data members are usually maintained to store values common to entire
class.
- There is only one copy of this data used by entire class which is shared by all the object of that class.
- It is visible only with in the class, however its life time is the entire program.
Ques 13. What are
static member method?
Ans:- A static member method is a member method which uses
only static data members only.
Ques 14 Discuss scope
and visibility rule of java.
Ans Java offers following levels of scope and visibility.
i.
Data declared at the class level can be used by or is
visible to all methods in that class.
ii.
Data declared within a method can be used only in that
method or is visible only to that method and is called as local data.
iii.
Variables declared in block. i.e. local variables are
available to every method inside that block.
iv.
Variables declared in interior block are not visible
outside that block.
v.
Variables declared in exterior block are visible to the
interior block.
Ques 15:- Why is
information hiding necessary?
Ans :- Information hiding is necessary because of the
following reasons:-
i.
Users should not be concerned with unnecessary details.
ii.
Users may do harm if they try to modify the internals
of a class.
Ques 16 : Differentiate between Local variable and
Global Variable constructor and method
Ans
:-
|
Local Variable
|
Global Variable
|
|
1. A variable declared inside a
method or a block is called as local variable.
2. This variable is not accessible
outside the method of block in which it is declared
|
1. A class variable which is
available to the entire class and its members is called as global variable.
2. Any method or block inside the
class can access these variable.
|
Ques
17 Discuss hiding of global variable.
Ans
:- If a local variable has the same name as the global variable then on
using the variable name value of the local variable is accessible i.e. the
global variable is hidden. This is called as hiding of global variable.
Ques 18. Difference between class variable and instance
variable.
|
Class Variable
|
Instance Variable
|
|
1. Any data member that is declared once for a class and
all the object of this class share this data member is said to be a class
variable.
2. A single copy of the variable accessible to all objects
is available in the memory.
3.Keyword static is used to declare a variable.
|
1. A data member that is created for every object of the class and is not shared is called as
instance variable.
2.As many copies of the variable are available in the
memory as many number of objects.
3. Normal variable declaration is used.
|
Ques 19 What is inheritance and how is it useful in Java? [2008]
Ans The process to aquire
properties of an existing class is called inheritance.
It provides reusability to a
class. It can be useful to add more properties to an existing class without
modifying existing class
Ques What does the following
means? [2008]
Employee staff=new
Employee()
Ans:= Given statement will create an object names as staff
for class Employee.
ques
Enter any two varibles through constructor paramenter and write a program to
swap and print the values. [2005]
class
swap
{
int
x,y;
swap(int
p, int q)
{
x=p;y=q;
}
void
swapping()
{
int
t;
t=x;
x=y;
y=t;
System.out.println(x+"
"+y);
}
}
class
check
{
public
static void main(String args[])
{
swap
obj=new swap(5,10);
obj.swapping();
}
}
PROGRAM 1 Define
a class electricity with
member data:- cno (connection number as integer), cname
(consumer name as string), ccap (connection capacity as
interger),,unit ( unit consumed), bill
as double.
Member function:- electricity(int ,String,int, int )//
//to initialize cno,cname ccap and unit .
int mincharge() // returns the minimum bill depending upon
connection capacity. If ccap is 1 kw
then mincharge is Rs150, if ccap is 2kw – 3kw then mincharge is Rs300 , for
ccap more then 4 kw then mincharge will
be Rs500
void calculate_bill() // calculates bill for first 100 units
1.80 Rs/unit, next 200 units 2.50 Rs/unit, above 300 units 3.20
Rs/unit
void display()// displays bill in proper format.
import
java.util.*;
class
electricity
{
private int
cno,ccap,unit;
private
String cname=new String();
private
double bill;
public
electricity(int cn,String n,int cc,int u)
{
cno=cn;
cname=n;
ccap=cc;
unit=u;
bill=0.0;
}
int
mincharge()
{
if(ccap==1)
return 150;
else
if(ccap==2 || ccap==3)
return 300;
else
return 500;
}
void
calculate_bill()
{
if(unit<=100)
bill=unit*1.80;
else if(unit<=200)
bill=180+(unit-100)*2.5;
else
bill=680+(unit-300)*3.20;
if(bill<mincharge())
bill=mincharge();
}
void
display()
{
System.out.println(
"connection number "+cno);
System.out.println(
"name "+cname);
System.out.println(
"connection capacity "+ccap);
System.out.println(
"units "+unit);
System.out.println(
"bill "+bill);
}
};
class
program
{
public
static void main(String args[]) throws Exception
{
electricity
ob=new electricity(2,"raju",3,345);
ob.calculate_bill();
ob.display();
}
}
PROGRAM
2 define a class distance with member function with member function feet
and inch
as integer. Member function are distance(int ,int) //to initialize distance in feet and inches. int
convert()// returns the distance in inches. void display() display
the distance in feet and inches. Use the above class definition to input the
dimensions of the room and calculates the volume in inch3 and area
in inch2.
class distance
{
private int feet, inch;
public distance(int f,int i)
{
feet=f;
inch=i;
}
public int convert()
{
return feet*12+inch;
}
void display()
{
System.out.println( feet+" feet "+inch+"
inch");
}
};
class multiobject
{
public static void main(String args[])
{
distance len=new distance(10,7);
distance wid=new distance(8,9);
distance hei=new distance(9,5);
int l,b,h,a,v;
l=len.convert();
b=len.convert();
h=hei.convert();
a=l*b;
v=l*b*h;
System.out.print( "length is");
len.display();
System.out.print( "Width is");
wid.display();
System.out.print( "height is");
hei.display();
System.out.println( "area is"+a);
System.out.println( "volume is"+v);
}
}
PROGRAM 3 define a class quadratic equation with
the member function as a, b and c as integer representing
the coefficient of the quadratic equation. quadratic(int,int,int)// initialize the
a,b,and c. void properties()// display the properties of the quadratic
equations.
void roots() displays the roots of the quadratic equations.
Use above class definition to input coefficient of the
quadratic equation and display its properties and roots.
import java.util.*;
class quadratic
{
private int a,b,c;
quadratic( int p,int q,int r)
{
a=p;
b=q;
c=r;
}
void properties()
{
int q=b*b-4*a*c;
if(q<0)
System.out.println( "roots are imaginary");
else if(q==0)
System.out.println( "roots are real and equal");
else
System.out.println( "roots are real and unequal");
}
void roots()
{
double q;
double x1,x2;
q=b*b-4*a*c;
if(q>=0)
{
x1=(-b+Math.sqrt(q))/2*a;
x2=(-b-Math.sqrt(q))/2*a;
System.out.println( x1+"\t"+x2);
}
}
};
class root
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int a,b,c;
System.out.println( "enter coefficient of quadratic
equation");
a=Sn.nextInt();
b=Sn.nextInt();
c=Sn.nextInt();
quadratic obj=new quadratic(a,b,c);
obj.properties();
obj.roots();
}
}
Specify the Output
Consider the following program code:
class scope
{
int value=5;
void fun1()
{
System.out.println(value+" ");
int value=10;
fun2(value);
System.out.println(value+" ");
fun3();
System.out.println(value+" ");
}
void fun2(int value)
{
System.out.println(value+" ");
value=20;
System.out.println(value+" ");
}
void fun3()
{
System.out.println(value+" ");
value=30;
}
};
class check
{
public static void main(String args[])
{
scope obj=new scope();
obj.fun1();
}
}
OUTPUT is:-
5 //value of
global variable value is printed
10 //value of argument variable of fun2() value is printed
20 // modified value of argument variable of fun2() value is printed
10 //value of local variable of fun1()
value is printed
5 // value of global variable value is
printed
10 //value of local variable of fun1()
value is printed
PROGRAM 4 Write a class with name employee and basic as
its data member, to find the gross pay of an employee for the followinf
allowences and deduction. use meaningful varibles.
Dearness allowance=25% of basic pay.
House Rent Allowance=15% of basic pay.
Provident Fund=8.33% of basic
Net Pay=Basic Pay+Dearness Allowance++House Rent
Allowance
Gross Pay=Net Pay-Provident Fund [2005]
import
java.util.*;
class
employee
{
String
name=new String();
int basic;
employee(String
n,int b)
{
name=n;
basic=b;
}
void
calc_disp()
{
double
hra,da,pf,gs,net;
hra=0.25*basic;
da=0.15*basic;
pf=0.833*basic;
gs=basic+hra+da;
net=gs-pf;
System.out.println("Name\t"+name);
System.out.println("Basic\t"+basic);
System.out.println("Dearness
allowance\t"+da);
System.out.println("House
Rent Allowance\t"+hra);
System.out.println("Provident
Fund\t"+pf);
System.out.println("Net
Pay\t"+net);
System.out.println("Gross
Pay\t"+gs);
}
}
class emp
{
public static
void main(String args[]) throws Exception
{
Scanner
Sn=new Scanner(System.in));
String n=new
String();
int b;
System.out.println("enter
name");
n=Sn.nextLine();
System.out.println("enter
basic");
b=Sn.nextInt();
employee
obj=new employee(n,b);
obj.calc_disp();
}
}
PROAGRM 5 Define a class employee having the following description
Data members int pan to store
personal account number
Instance
variable String name to store name
Double
taxincome to store taxable income
Double
tax to store tax that is
calculated
Member functions:
input() store pan number,name,taxable income
calc() calculate tax for employee
display() Output details
WAP to copute the tax
to the given conditions and give output as per given format
Total Annual Taxable
Income Tax rate
Upto rs.100000 No
tax
From rs.100001 to
150000 10%
of income exceeding rs.100000
from rs.150001 to
250000 rs.5000+20%
of income exceeding rs.150000
Above 250000 rs.25000+30%
of income exceeding rs.250000
[2008]
Output:
Pan Number Name Taxincome Tax
…. ….. …… ….
….. ….. …… …..
import java.util.*;
public class employee
{
int pan;
String name;
double tax;
double taxincome;
public void input() throws IOException
{
DataInputStream in=new DataInputStream(System.in);
System.out.println("enter the name of employee");
name=in.readLine();
System.out.println("enter pan no");
pan=Integer.parseInt(in.readLine());
System.out.println("enter taxable income");
taxincome=Double.parseDouble(in.readLine());
}
public void calc()
{
if(taxincome<=100000)
tax=0;
if(taxincome>=100001 && taxincome<=150000)
tax=(((taxincome-100000)*10)/100);
else if(taxincome>=150001 &&
taxincome<=250000)
tax=5000+(((taxincome-150000)*20)/100);
else if(taxincome>250000)
tax=25000+(((taxincome-250000)*30)/100);
}
public void display()
{
System.out.println("pan number"+"
"+"name" +" "+"Taxincome" + "
"+"tax");
System.out.println(pan+" "+name+ " "
+taxincome+" " +tax);
}
}
PROGRAM TO PRACTICE
· Classes and Objects-
Q1: - Class - Date
Member data : dd, mm, yy as integer.
date(int d, int m, int y) //assign
d,m,y to dd,mm,yy respectively.
void
dispday() //add
suffix with dd 1,21,31 with st , 2,22
with rd, 3, 23 with rd other with th.
void dispmon() //displays
month in words as jan, feb etc.
void display() //if
date is 11/9/2001
then display 11th September
2003
Q2. Declare a
class with the following members to store the information about a Machine in a machine store-
Data members- machine_type (string), machine_no(long),
purchase price(double), and year of purchase(long)
Functions- void getdata() to read information about machine
void showdata() to
display the information about the machine.
Q3.
Define a class student
with
Member data: - rollno as int, name as
string, mark[5] int array of five
elements
average as int, grade as char.
void readdata() // input rollno, name and marks of
five subject.
void calculate_average() // calculates the average of all subject.
char status() // retruns P if student scores min 40
marks in all subjects otherwise returns ‘F’
void calculate_grade() //calculates grade if student is passed in all subject.
Otherwise grade is F
|
Average
|
>=85
|
>=65
- <85
|
>=55
- <65
|
>=40
- <55
|
<40
|
|
Grade
|
A
|
B
|
C
|
D
|
F
|
void
display() // displays the details of the
students.
Q4. Define a class triangle with a member data a, b and c as integer as sides
of the
Triangle.
void readdata() input sides of the triangle.
int ispossible() retruns
1 if triangle is possible with the given sides.
void area() calculates
and displays the area of the triangle.
Use above class definition to input three sides of the triangle and
display area of the triangle if triangle is possible.
Q5.
Define a class shape with
member data as area ( as double ), perimeter( as double)
with member function shape()
which initialize area and perimeter as zero.
void square(int s) calculate area and perimeter of
square.
void rectangle(int l,int b)
calculate area and perimeter of rectangle.
void equilateral( int a)
calculate area and perimeter of equilateral
triangle.
void rightanglet(int h, int b) calculate area and perimeter of
right angle triangle.
void circle(int r) calculate area and perimeter of circle.
void display() display the area and perimeter.
Write as menu driven program to use above
class to find area and perimeter of the
given shapes.
QUES 6.There is a class Taxpayer whose class description is
given below: Class name: TaXpayer
Data members/instance variables: pan to store the personal
account number, name to store the name of a person ,.taxableinc to store the
total annual taxable income, tax to store the tax that is
calculated
Member functions/methods:Taxpayer( )
//constructor, void inputdata( ) //to enter the data for a taxpayer, void
displaydata( ) //to display the data for a taxpayer, void
computetax( ) //to compute tax for a taxpayer The tax is calculated according to the
following rules:
TOTAL ANNUAL TAXABLE INCOME RATE OF TAXATION
Up to 60000 - 0%
,
Any amount above
60000 but up to 150000 - 5%,
Any amount above
150000 but up to 500000 - 10%
Any amount above 500000 - 15%
Ques 7 Class
telcall calculates the monthly phone bill of a consumer. Some of the members of
the class are given below:
Class name: telcall
Data members/ instance variables:
phno :
phone number
name :
name of consumer
n :
number of calls made (integer)
amt :
bill amount
Member functions/ methods:
telcall(int x, char y[20], int k) :
parameterised constructor to assign values to data members
void
compute() : to calculate the phone bill amount based on the slabs given
below
void
display() : to display the details in the specified format
number of calls: rate
1 -100 : Rs. 500/- +rental charge only
101 -200 : Rs. 1.00/-
per call + rental charge
201 -300 : Rs. 1.20/-
per call + rental charge
above 300 : Rs. 1.50/- per call + rental charge
the calculations need to be done as per the slabs.
QUESTION 8:-
Class employee contains the following member:
Class name: employee
Data members/instance variables:
empname . : to
store the name of employee int empcode
: to store the employee code.
basicpay : to
store the basic pay of the employee Member functions/methods:
employee() :
constructor to initialize all data members/instance variables to null or 0
employee( char n, int p, double q) : parameterised constructor to assign name, employee code and basic salary to data members /
instance variables.
double salarycal() : to
compute and return the total salary of the employee The salary is calculated according
to the following rules:
Salary = basic Pay +
HRA + DA,
HRA = 30% of basic pay,
DA = 40% of basic
pay.
special allowance= if salary is >=10000 then 20% of
salary otherwise 15% of salary.
Total salary = salary +special allowance. Specify the
employee class giving the details of the two constructors and the function
double
salarycal( ) only. You do not need to write the main
function
Question 9:-
Create a class salary calculation as given:
Class name:- SalaryCalculation
Data member name(String type), basic pay, specialalw,
coveyanceAlw, gross, pf, netsalary, annualsal
Member function of
class:
SalaryCalculation() - a constructor to assign name of
employee name, Basic salary of your choice and conveyance allowance as Rs. 1000
void Salarycal() - to calculate other
allowance and salaries as given:
Specialalw=25%
of basic salary
Gross=basic+specialalw+conveyanceAlw.
netSalary=gross-pf
annualsal=12
month net salary.
void display() -
to print name and other data member of class with suitable heading.
Write a main program
to create the object of the class. Calculate allowances, salary and print all
the data of an employee.
Question 10:
A class dataprocess
is defined as follows:
Data members:- N(long
integer variable, ch( character variable)
Member function:
Dataprocess(long x,
char st)- parameterized constructor to store value of variable x to N,
character stored in st to ch.
long FindProduct() - to find and return product of even digits
present in N. do not use (%) operator) for extracting digits. Make suitable use
of do-while loop.
void change()- to
convert the character stored in ‘ch’ into the opposite cas. Print the original
and the new character.
Write a main program to input a number and a character . create
the suitable object that activates the parameterized constructor and by invoking suitable function
print the required result.
Question 11;-
Create a class series
whose members are as given:
Data members:- F,S,limit,sum
Member function:-
Series(int n)- a parameterized constructor to assign 0 to F and 1 to
S as the first two terms of Fibonacci series, n to limit as total number of
terms to be printed
void printseris() - to print Fibonacci
series[0,1,1,2,3,5,8,13……….limit]
