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Laboratory 3:
Course Code: CPCS-202
Course Name: Programming I
Introduction: The purpose of this Lab. is to familiarize you how to solve
practical problems programmatically; you will practice on elementary
programming using primitive data types, variables, constants, operators,
expressions, and input and output. Also, you will learn how to diagnose errors
that may occur when a program is compiled or executed.
Objective: This lab teaches you the following topics.
■To write Java programs to perform simple calculations (§2.2).
■ To obtain input from the console using the Scanner class (§2.3).
■ To use identifiers to name variables, constants, methods, and classes (§2.4).
■ To use variables to store data (§§2.5–2.6).
■ To program with assignment statements and assignment expressions (§2.6).
■ To use constants to store permanent data (§2.7).
■ To declare Java primitive data types: byte, short, int, long, float, double,
and char (§2.8.1).
■ To use Java operators to write numeric expressions (§§2.8.2–2.8.3).
■ To use shorthand operators (§2.10).
■ To cast the value of one type to another type (§2.11).
■ To represent a string using the String type (§2.15).
■ To distinguish syntax errors, runtime errors, and logic errors and debug
errors (§2.17).
■ (GUI) To obtain input using the JOptionPane input dialog boxes (§2.18).
Activity 1: write a program in java to interchange (swap) values of two
variables with a use of 3rd variable.
Input: value num1 and num2
Processing: swapping values of num1 to num2 and num2 to num1 using a
third variable num3.
Output: Display value of num1 and num2 after swap operation.
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Solution1:
A. File -> New project-> Project Name: Lab3Activities , Main Class
Name  Swap2Nos  click Finish Button
B. Write Code inside the main method and test it by compiling (F9)
and running (Shift + F6) your code.
/* Swap Two Numbers Using Third Vairable*/
public class Swap2Nos {
public static void main(String[] args) {
// declare variables num1, num2, num3 of the type int
int num1, num2, num3;
// assign values to num1 and num2
num1=50;
num2=100;
// display Number before swap
System.out.println("Before Swap Number 1 =" + num1 + " Number 2=
"+ num2);
// swap logic starts from here
num3=num1;
num1=num2;
num2=num3;
// swap logic ends here
// display Number After Swap
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System.out.println("After Swap Number 1 =" + num1 + " Number 2=
"+ num2);
}
}
Activity 2: Write a program in java that obtains minutes and remaining
seconds from an amount of time in seconds. For example, 500 seconds
contains 8 minutes and 20 seconds.
Output of the program can be:
A. File -> New File-> File Type : java main class  next
B. Class Name  ConverSecMin click Finish Button
C. Write Code inside the main method and test it by compiling (F9)
and running (Shift + F6) your code.
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Reading Data from keyboard using Scanner Class
Step 1: import java.util.Scanner; /*before your class statement*/
Step 2: create Scanner object to obtain input from command window
Scanner input = new Scanner ( System.in );
/* input is object name of Scanner Class you may write any object name like
in , read etc. */
Step 3: input.nextInt(); // read number
Activity 3 // let's look at a simple program that computes the area of a
circle.
A. File -> New ->Java Main Class-> named it ComputeCircleArea
B. Write Code inside the main method and test it by running the
application.
The program can be expanded as follows:
// Step 1 : import java.util.Scanner;
public class ComputeCircleArea
{
public static void main(String[] args) {
// Step 2: declare variables
// Step 3: Read in radius
// Step 4: Compute area
// Step 5: Display the area
} }
// Example a simple program that computes area of a circle.
import java.util.Scanner;
public class ComputeArea {
// Declare a constant PI
static final double PI =3.1414;
public static void main(String[] args) {
double radius, area; // variable declaration
Scanner in = new Scanner (System.in);
System.out.println("Enter Raduis");
// read radius from the system
radius = in.nextDouble();
area=PI*radius*radius;
System.out.println("Area of Circle\t"+ area);
}}
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Arithmetic Expressions:
Writing numeric expressions in Java involves a straightforward translation of
an arithmetic expression using Java operators. For example, the arithmetic
expression
Can be translated into a Java expression as:
(3 + 4 * x) / 5 – 10 * (y - 5) * (a + b + c) / x + 9 * (4 / x + (9 + x) / y)
Activity 4: The problem is to write a program that computes loan payments.
The loan can be a car loan, a student loan, or a home mortgage loan. The
program lets the user enter the interest rate, number of years, and loan amount,
and displays the monthly and total payments. The formula to compute the
monthly payment is as follows:
Given the monthly interest rate, number of years, and loan amount, you can
use it to compute the monthly payment.
Here are the steps in developing the program:
1. Prompt the user to enter the annual interest rate, number of years, and loan
amount.
2. Obtain the monthly interest rate from the annual interest rate.
3. Compute the monthly payment using the preceding formula.
4. Compute the total payment, which is the monthly payment multiplied by 12
and multiplied by the number of years.
5. Display the monthly payment and total payment.
// Following is complete program for activity 4.
// File / class name ComputeLoan.java
import java.util.Scanner;
public class ComputeLoan {
public static void main(String[] args) {
// Create a Scanner
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Scanner input = new Scanner(System.in);
// Enter yearly interest rate
System.out.print("Enter yearly interest rate, for example 8.25: ");
double annualInterestRate = input.nextDouble();
// Obtain monthly interest rate
double monthlyInterestRate = annualInterestRate / 1200;
// Enter number of years
System.out.print( "Enter number of years as an integer, for example 5: ");
int numberOfYears = input.nextInt();
// Enter loan amount
System.out.print("Enter loan amount, for example 120000.95: ");
double loanAmount = input.nextDouble();
// Calculate payment
double monthlyPayment= loanAmount * monthlyInterestRate / (1 - 1 /
Math.pow(1 + monthlyInterestRate, numberOfYears * 12));
double totalPayment= monthlyPayment * numberOfYears * 12;
// Display results
System.out.println("The monthly payment is " + (int)(monthlyPayment
* 100) / 100.0);
System.out.println("The total payment is " + (int)(totalPayment * 100) /
100.0);
}
}
Increment and Decrement operators:
Aside from the basic arithmetic operators, Java also includes a unary
increment operator (++) and unary decrement operator (--). Increment and
decrement operators increase and decrease a value stored in a number variable
by 1. For example, the expression, count = count + 1; //increment the value of
count by 1 is equivalent to, count++;
The increment and decrement operators can be placed before or after an
operand.
When used before an operand, it causes the variable to be incremented or
decremented by 1, and then the new value is used in the expression in which it
appears.
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For example,
int i = 10,
int j = 3;
int k = 0;
k = ++j + i; //will result to k = 4+10 = 14
When the increment and decrement operators are placed after the operand, the
old value of the variable will be used in the expression where it appears. For
example,
int i = 10,
int j = 3;
int k = 0;
k = j++ + i; //will result to k = 3+10 = 13
Conversion between Data Types:
We can convert the value of a variable to the format of another variable of
different type and make an assignment between them, conversion is different
from another operation called casting, Following discussion shows the
difference between them.
int i; float f; double d;
i = 1;
f = 4.4f;
d = 5.5;
d = i;
i = (int)f;
f = (float)d;
System.out.println("i = " + i + " f = " + f + " d = " + d);
The above code does the following:
● Converts the value of i to double and stores it in d. This conversion is done
automatically by the compiler, because double data type is normally wider
than int, there is absolutely no risk storing int in double.
● In the following two statements, notice that we but a large value into a
smaller data type, in this case, a possible loss of data occurs in which we have
to be aware of. Because that, compiler (by default) refuses to store float value
in int, or double in float. Because of that, we use casting to tell to compiler
that we know what we are doing!
Another way to convert between variables is using some defined methods that
converts between variables.
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One of them is a well known method that converts a String to integer which is
Integer.parseInt() method, the following example shows how to use it.
String s = "115";
int x = Integer.parseInt(s);
x++;
System.out.println(x); //prints 116
Similarly, we can also use Double.parseDouble(), Float.parseFloat() and
Long.parseLong().
A common method among all objects in Java is toString() method which
converts the object to a string, toString() method will be covered in more
details later. Types of conversion mentioned above are called explicit
conversion, because we request that.
Activity 5: gives a program that displays the sales tax with two digits after
the decimal point.
Program: SalesTax.java
import java.util.Scanner;
public class SalesTax {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter purchase amount: ");
double purchaseAmount = input.nextDouble();
double tax = purchaseAmount * 0.06;
System.out.println("Sales tax is " + (int)tax*100/100.0) ;
}
}
Using JOptionPane to get input
Another way to get input from the user is by using the JOptionPane class
which is found in the javax.swing package. JOptionPane makes it easy to pop
up a standard dialog box that prompts users for a value or informs them of
something.
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Given the following code,
Activity 6:
import javax.swing.JOptionPane;
public class GetInputFromKeyboard
{
public static void main( String[] args ){
String name = "";
name = JoptionPane.showInputDialog("Please enter your name");
String msg = "Hello " + name + "!";
JOptionPane.showMessageDialog(null, msg);
}
}
Home Activities: (One week to submit)
1. Which of the following identifiers are valid? Which are Java keywords?
applet, Applet, a++, ––a, 4#R, $4, #44,
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apps, class, public, int, x, y, radius
2. Translate the following algorithm into Java code:
Step 1: Declare double variable named miles with initial value 100;
Step 2: Declare a double constant named MILES_PER_KILOMETER
with value 1.609;
Step 3: Declare a double variable named kilometers, multiply miles and
MILES_PER_KILOMETER, and assign the result to kilometers.
Step 4: Display kilometers to the console. What is a kilometer after Step
4?
4. Identify and fix the errors in the following code:
public class Test {
public void Main(string[] args) {
int i;
int k = 100.0;
int j = i + 1;
System.out.println("j is " + j + " and k is " + k);
}
5. Write a class called TimeConvert, which when executed, prompts the
user for to enter a Number of seconds, and then it prints out the
equivalent number of days, hours, and minutes. You do not have to
worry about excess seconds.
A sample run is given below.
Enter total number of Seconds:
84939
84939 second is equal to:
0 day
23 Hours
35 minutes
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[Hint: Use the Scanner class to read input from the command console]
6. Write a program in Java to interchange values of two variables without
using the third variable. If A=10 , B=20 after interchange A=20,
B=10
7. Write a program that reads an integer between 0 and 1000 and adds all
the digits in the integer. For example, if an integer is 932, the sum of all
its digits is 14. [Use the % operator to extract digits, and use the /
operator to remove the extracted digit. For instance, 932 % 10 = 2
and 932 / 10 = 93]
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9. Using JOptionPane, ask for three words from the user and output those
three words on the screen. For example,
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Lab Report:
The laboratory report of this lab (and also all the following labs in
this manual) should include the following items/sections:
- A cover page with your name, course information, lab number and
title, and date of submission.
- A summary of the addressed topic and objectives of the lab.
- Implementation: a brief description of the process you followed in
conducting the implementation of the lab scenarios.
- Results obtained throughout the lab implementation, the analysis
of these results, and a comparison of these results with your
expectations.
- Answers to the given exercises at the end of the lab. If an answer
incorporates new graphs, analysis of these graphs should be
included here.
- A conclusion that includes what you learned, difficulties you
faced, and any suggested extensions/improvements to the lab.
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