# Lab Assignment 9-10 Local Variables

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Lab Assignment 9-10
1 Background
This document contains assignments to be completed as part of the hands on for the subject
Inroduction to Java programming and JEE framework.
Assignment 1: Local Variables
Objective: Understand the usage of local variables
Problem Description: To create different types of local variables and display them
Step 1: Type the below program in the textpad, save and compile the program
// Program to understand local variables and literals
class Variable {
public static void main (String args[]){
intintVal;
floatfloatVal = 250.5f;
doubledoubleVal = 2500.5;
booleanboolVal = true;
System.out.println(“Integer\t:” + intVal + “\nFloat\t:” +
floatVal+”\nDouble\t:” + doubleVal + “\nBoolean\t:” + boolVal);
}
}
Step 2: Observe that there is a compilation error. Debug the code so that it compiles and executes
successfully.
Note:Accessing an uninitialized local variable will result in a compiletime error. If you cannot initialize your local variable where it is
declared, make sure to assign a value before you attempt to use it.
Summary of this assignment:
In this assignment, you have learnt
• How to use local variables in Java
Assignment 2: Operators
Objective: Understand the various operators in Java
Problem Description: To implement and understand the usage of modulus operator, string
concatenation, equality operator and logical operators in Java.
Step 1: Type the below program in the textpad, save, compile and execute
// Program to understand different types of operators
class Operator{
public static void main(String[] args){
intintVal=10;
floatfloatVal=3.0f;
boolean bool1 = true;
boolean bool2 = false;
boolean bool3 = true;
// Arithmetic : Modulus operator
System.out.println(“Arithmetic”);
System.out.println(intVal + ” % ” + floatVal + “=” +
(intVal % floatVal));
System.out.println();
// String Concatenation : Observe the difference
System.out.println(“String Concatenation”);
System.out.println(“Day ” + 2 + ” Session”);
System.out.println(“\n” + 2 + 3 +”\n” +(2+3));
System.out.println();
// Relational: Equality operator
System.out.println(“Relational”);
System.out.println(intVal + ” == ” + floatVal + ” = ”
+(intVal==floatVal));
floatVal = 10.0f;
System.out.println(intVal + ” == ” + floatVal + ” = ”
+(intVal==floatVal));
System.out.println();
bool2 = false;
if(bool1 || (bool1 && (bool2=false))){
System.out.println(“Success”);
}
else{
System.out.println(“Failure”);
}
System.out.println(“bool2 value : ” + bool2);
}
}
Summary of this assignment:
In this assignment, you have learnt
• Usage of some operators available in Java
Assignment 3: Boolean Data Type
Objective: Understand the Boolean data type
Problem Description: To implement and understand the usage Boolean datatype in Java
Step 1: Type the below program in the textpad and save the file
Step 2: When executed, the output is :
Failure
bool2 value : true
Press any key to continue . . .
Step 3: Make changes to the code so that the output reads :
Success
bool2 value : true
Press any key to continue . . .
Note: The logical operators and the Boolean operators may be changed to achieve this result.
Although the if control structure is used here, the focus is on the operators and Boolean datatype
class Operator{
public static void main(String[] args){
boolean bool1 = false;
boolean bool2 = true;
boolean bool3 = true;
if(bool1 && (bool1 && (bool2=false))){
System.out.println(“Success”);
}
else{
System.out.println(“Failure”);
}
System.out.println(“bool2 value : ” + bool2);
}
}
Summary of this assignment:
In this assignment, you have learnt
• Boolean data type and operators
Assignment 4: Control Statement
Objective: Understand control statements
Problem Description: To implement control flow statements break and continue
Step 1: Type the below programs in the textpad, save, compile and execute
Program 1:
//Program to understand the loop and break
class Control{
public static void main(String args[]){
booleanbool = true;
for(int i= 0; i<5 ; i++){
for(int j = 0; j<10; j++){
System.out.print(j +”\t”);
if(j > 5){
break;
}
}
System.out.println(“Outer Loop”);
}
System.out.println(“End”);
}
}
Program 2:
//Program to understand the loop and continue
classControlContinue{
public static void main(String args[]){
booleanbool = true;
for(int i= 0; i<5 ; i++){
for(int j = 0; j<10; j++){
System.out.print(j +”\t”);
if(j > 5){
System.out.println();
continue;
}
}
System.out.println(“Outer Loop”);
}
System.out.println(“End”);
}
}
Note:
• You can’t use a number or anything that does not evaluate to a Boolean value
as a condition in selection / iteration statement
• You can use break inside a looping statement without including if construct.
Summary of this assignment:
In this assignment, you have learnt
• How to use break and continue with the looping statement.
Assignment 5: Switch case statement
Objective: Understand the concept of conditional case statements using switch cases.
Problem Description: A java program needs to be written to display the range of marks based on the
A 80-100
B 73-79
C 65-72
D 55-64
E <55
Step 1: Create a class called SwitchCase with the main method
Step 2: Create a character variable for storing the grade with a default value of B
Step 3: Write the java code to implement the calculation of grades as given in the table. If any other
grade is provided , the program must display a message “Grade does not exist”,for valid grades it must
display the range of marks as given in the table.
Step 4: Change the values of the grade variable and test the working of the program for all the grades.
Summary of this assignment:
In this assignment, you have learnt
• Switch case statements
Assignment 6: Classes and Objects
Objective: Understand and implement the concept of encapsulation and abstraction.
Problem Description:
Implement the following class diagram using Java.
Note:
• Using a class , you can create any number of objects
• For every instance variable there should be a setter and getter method
associated to it. Setter method is to set the value of the instance variable and
getter method is to return the value of the instance variable
• studentType instance variable can have ‘F’ (fresher) or ‘L’ (lateral)
Step 1: Define a class “Student” and save it in Student.java
Step 2: Define all the member methods of Student Class
Step 3: Define a class “CourseManagement” with main method and save it in
CourseManagement.java
a. In the main method, assign the student details in the corresponding temporary
variables.
b. Create a reference variable with the name student and instantiate the same
c. Invoke the corresponding setter methods to set the instance variable with the given
values stored in temporary variables.
d. Using getter methods, display the student details.
Step 4: Compile the program, fix the errors if any
Step 5: Execute the program and verify the output
Summary of this assignment:
In this assignment, you have learnt
• How to implement getter and setter methods
• How to create reference variables
• How to create an object
Student
-studentId : integer
-studentType:char
+setStudentId(id:int):void
+setStudentType(type:char):void
Assignment 7: Default Constructor
Objective: Understand the concept of Default Constructor.
Problem Description:
Enhance the Assignment 4 and do the necessary modification as mentioned below:
Step 1: Define constructor in Student class
Student (): initialize the instance variables with 10 and ‘F’ (indicated fresher) respectively
Step 2: Define a main method
a. In the main method, create a reference variable with the name student.
b. Create an object of type Student and assign it to reference variable named
student.
c. Using getter methods, display the student details.
Step 3: Compile the program, fix the errors if any
Step 4: Execute the program and verify the output
Student
-studentId : integer
-studentType:char
+Student()
+setStudentId(id:int):void
Estimated time: 15 mins
Summary of this assignment:
In this assignment, you have learnt
• How to implement default constructor
• How to use the constructor for initializing the objects
Assignment 8: Default and Parameterized constructors
Objective: Understand the concept and working of default and parameterized constructor.
Problem Description: Create a class called UserType and create a default and a parameterized
constructor. Invoke these constructors through two different objects of the UserType class.
public class UserType {
String name;
UserType(String parameterVal)
{
name = parameterVal;
}
UserType()
{
name = “Student”;
}
public static void main(String args[]) {
UserType usertype1 = new UserType(“Faculty”);
UserType usertype2 = new UserType();
System.out.println(usertype1.name);
System.out.println(usertype2.name);
}
}
Summary of this assignment:
In this assignment, you have learnt about
• Default and
• Parameterized constructors
Optional Assignment 9: ElectricityBill with getter and setter
methods
Objective: To write a program with getter and setter methods.
Problem Description: Create a class called ElectricityBillwhich has
1. Four data members customerId (int), customerName(String), previousReading(float),
2. Introduce setter and getter methods for assigning and retrieving values for the instance
variables.
3. Write a public method called printDetails with the following prototype
public void printDetails() which prints all the details of the ElectricityBill such as customerId,
customerName, NoOfUnits.
4. Write a main method which creates an object of ElectricityBillinvokes the setter and getter
methods And also prints the electricity bill details by calling printDetails method
Assignment 10: this keyoword
Objective: To write a Java class to understand the concept of this keyword.
Problem Description: Customer class is created such that the name of method arguments and the
name of instance variables are one and the same.
Step 1: Create a folder Assignment1 under your work directory
Step 2: Create a Customer class as given below
FileName: Customer.java
/*
* This java file contains a class having the attributes of a
* Customer and has a parameterized constructor to initialize the
* instance variables
*/
/**
* This class has four attributes customerId, customerName,
* customerTelNo, customerEmail and uses the parameterized
constructor
* to initialize the instance variables
* Date: 16-Mar-2007
*
* @version 1.0
*/
class Customer
{
privateintcustomerId;
private String customerName;
/**
* Parameterized Constructor: Creates a customer Object and
* initializes the instances variables with the supplied values.
* Since the method arguments name and instance variable names
* are similar we have to use this keyword which has a
* reference to the current object
*/
Customer(intcustomerId, String customerName)
{
this.customerId= customerId;
this.customerName= customerName;
}
/**
*This method displays the customer details
*@param void
*@return void
*/
public void displayCustomer()
{
System.out.println(“Customer Id :” + customerId);
System.out.println(“Customer Name :” + customerName);
}
/**
* Creates an object of the Customer class and
* and invokes the method displayCustomer using the object to
* print the customer details
* @paramargs Command line arguments
*/
public static void main(String argv[])
{
Customer c1=new Customer(1001, “John”);
c1.displayCustomer();
}
}
Step4: Compile and execute the above program. The output should come up.
Customer Id: 1001
Customer Name: John
Step 5: Modify the program by eliminating the “this” keyword in all the statements inside the
parameterized constructor. Save the changes and analyze the results after execution.
Summary of this exercise:
You have just learnt
• How to write parameterized constructor in java using this keyword.
Note: this keyword acts as a reference to the current object with which the
parameterized constructor is invoked.
this keyword must be used within a parameterized constructor when the instance
variables’ name and arguments name are same.
Assignment 11: Reference variable as an argument to a method
Objective: Understand the usage of “this” keyword.
Problem Description: Implement the class diagram Using Java
Step 1: Define a class Student ,
• Define two constructors
o Default constructor: Used to increment the value of studentId for each
objects of Student class. studentId should start from 550.
o Parameterized constructor: Constructor with three arguments
StudentType(H/D),firstName and lastName
studentName=firstName+lastName
o displayDetails (Student obj):Should accept the object as an argument and
display the details like studentId, studentType, studentName of that object
Step 2: Define a main method ,
• In the main method
o Create an object of Student(‘D’,”Bony”,”Thomas”) and assign it to reference
variable studentOne;
o Call the displayDetails() method and display the details of studentOne
o Create an object of Student(‘H’,”Dinil”,”Bose”) and assign it to reference
variable studentTwo;
o Call the displayDetails() method and display the details of studentTwo
Step 3: Compile the program, fix the errors if any
Step 4: Execute the program and verify the output
Summary of this assignment:
In this assignment, you have learnt
• How to use this, passing object to an argument, Overloaded constructors
Assignment 12: User Input(Command Line Arguments)
Objective: To work with command line arguments.
Student
-studentId : integer
-studentType:char
-studentName:String
+Student()
+Student(char sType,Stringfname,Stringlname)
+displayDetails(Student):void
Step 1: Create a folder Assignment3 under your work directory
Step 2: Open a text editor, notepad or Dos Editor and type the following:
/* This file is a demo Java program which depicts the concept of
* command line arguments
*/
/**
* This class contains the main method which accepts the
* two integer values as command line arguments and displays the
sum.
* Date: 20-Apr-2007
*
* @version 1.0
*/
public class CommandLineArgs {
/**
* Starting point of the application.
* Expects exactly two command line arguments else
* prints an error message and terminates the program
* otherwise it will parse the arguments to integers and
* displays the sum by adding them
* @paramargs Command line arguments
*/
public static void main(String args[])
{
if (args.length< 2 || args.length> 2)
{
System.out.println(“Invalid no of arguments”+
“Supply exactly two arguments”);
System.exit(0);
}
System.out.println(args[0]+” “+args[1]);
int x=Integer.parseInt(args[0]);
int y=Integer.parseInt(args[1]);
System.out.println(x+y);
}
}
Step 3: Save the file as ‘CommandLineArgs.java’
Step 4:Compiling the program. Close the editor. Now compile your program using the command
line:
javac CommandLineArgs.java
Step 5: Run your program using the command line:
javaCommandLineArgs
Check the output of the program.
Now run the program using the command line:
javaCommandLineArgs 5 6
Now the output will be 5 6 and 11
Hint: Refer to Javadoc for the wrapper classes
Summary of this exercise:
You have just learnt
• How to pass command line arguments into a java program
• The arguments are passed as array of Strings.
• How to convert the String value to its respective integer value in order to perform numerical
operation on it
Assignment 13: Java Doc Exploratory assignment on Strings
Objective: To explore and understand the Java Doc. Create a program with the help of java doc. (hint
use String)
Problem Description: Create classes called which does the following:
1. Takes User name as input
2. Display length of the string
3. Displays output as Hi <username>
4. Convert User name to lower case
5. Convert User name to upper case
6. Check whether the name is starting with ‘a’
Summary of this assignment:
In this assignment, you have learnt
• To use Java Doc to seek help on existing classes
Assignment 14: Static variable, block and method
Objective: To write a Java class to understand the concept of static keyword.
Problem Description: To the Customer class created in Assignment 1 of Day 2, modify the Customer
class so as to help us to keep track of the number of Customer objects created during runtime.
Step 1: Create a folder Assignment5 under your work directory
Step 2: Copy the Customer.java file created in Assignment 1 of Day 2 into this folder.
Step 3: Do the necessary modifications as conveyed below.
Filename: Customer.java
/**
* This java file contains a class having the attributes of a
* Customer and has a parameterized constructor to initialize the
* instance variables.
* Demonstrates the usage of static block, static variables and
static
* methods
*/
/**
* This class has four attributes customerId ,customerName,
* customerTelNo, customerEmail and uses the parameterized
constructor
* to initialize the instance variables
* Also declare a static variable named noOfCustomers which help us
* to keep track of the number of customer objects created during
* runtime.
* Date: 20-Apr-2007
*
* @version 1.0
*/
class Customer
{
/* Static block – A block of statements written to
* initialize static variables
* The statements inside the static block will get
* executed only once when the class is loaded
* by the JVM
*/
static
{
/* Assume that we already have 50 customers. Hence the
* static variable noOfCustomers has to be initialized
* to 50
*/
noOfCustomers = 50;
}
/* declaration of instance variables
* these variables are available for every objects created
*/
privateintcustomerId;
private String customerName;
privateintcustomerTelNo;
private String customerEmail;
/* declaration of static variables (class variables )
* this is common for all the objects created
*/
staticintnoOfCustomers;
/**
* Parameterized Constructor: Creates a customer Object and
* initializes the instances variables with the supplied values.
* Since the method arguments name and instance variable names
* are similar we have to use this keyword which has a
* reference to the current object
*/
Customer(intcustomerId, String customerName, intcustomerTelNo,
String customerEmail)
{
this.customerId= customerId;
this.customerName= customerName;
this.customerTelNo= customerTelNo;
this.customerEmail= customerEmail;
/* increment the static variable by one since
* we have created one customer object */
noOfCustomers++;
}
/**
*This method displays the customer details
*@param void
*@return void
*/
public void displayCustomer()
{
System.out.println(“Customer Id :” + customerId);
System.out.println(“Customer Name :” + customerName);
System.out.println(“Customer TelNo : ” + customerTelNo);
System.out.println(“Customer Email Id : ” + customerEmail);
}
/**
*This method displays the count of
* the number of customer objects created during runtime.
* This is static method (class method) which can access
* only static variables
*@param void
*@return void
*/
public static void customerCount()
{
System.out.println(“No of Customers : “+ noOfCustomers);
}
/**
* Creates an object of the Customer class and
* and invokes the method displayCustomer using the object to
* print the customer details
* @paramargs Command line arguments
*/
public static void main(String argv[])
{
//creating customer object one
Customer c1=new Customer(1001, “John”, 465364,
“John@yahoo.com”);
//creating customer object two
Customer c2=new Customer(1002, “Jack”, 764755,
“Jack@yahoo.com”);
//display the count of customer objects
Customer.customerCount();
// c2.displayCustomer();
}
}
Step 4: Compile and execute the program. Analyze the results.
Step 5: Omit the class name alone and just say customerCount() alone within the code while
invoking the static method. Compile the program and analyze the results.
Step 6: Try invoking the static variable noOfCustomerswithin a non-static method displayCustomer()
and remove the comments in the last statement of the main method.
Compile the program and analyze the results.
Summary of this exercise:
You have just learnt
• When to go for static variables, and how to declare static variables
• When to go for static methods, and how to declare and implement static methods
• When to go for static block, and how to declare the same.
Note:
Static block: Used to initialize static variables. Statements inside the static block are
executed only once when the class loaded by the JVM.
Static variable (Class variables) – A single copy of the variable is retained and is shared
by all objects. Static numeric variables are Initialized to zero.
Static methods (Class methods) can access only static variables.

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