Lab Manual I · CSE 202

Java Syntax, Data Types & Control Flow

Set up the JDK and an IDE, then write a first Java program that uses variables, primitive types, type casting, if/switch decisions and the three loops.

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Before we start

Why this lab

Every Java program you write this semester — bank systems, threads, GUIs — is built from the same few pieces. Which ones?

Variables hold data, types say what kind of data, decisions choose a path and loops repeat work. This lab puts all of them in one program, Lab1Demo.

Lab 1 of 10

Lab at a glance

After this lab you can

Set up and verify a JDK (11+) with NetBeans, Eclipse or IntelliJ IDEA
Explain how source code becomes bytecode that the JVM runs
Declare variables of the eight primitive types and String
Apply widening and narrowing casts
Use if / else if / else and switch
Repeat work with for, while and do-while; control loops with break and continue

Before you start

Create folders and save files
Basic idea of variables, expressions, input and output
JDK 11+ and an IDE installed

Plan for the session

Theory recap
Walk through the program, section by section, and run it
In-lab tasks, shown to the instructor
Report exercises at home

Lab 1 of 10

Select a part to jump to it.

Install Java and NetBeans
Theory recap
Program design
Code walkthrough
Step-through traces: stack, heap and output
Expected output
Interactive demos
In-lab tasks
Lab report exercises
Viva questions and quiz

Setting up · 1 of 4

Which Java do you need?

A JDK (Java Development Kit): it contains the compiler javac and the runtime java. A JRE alone cannot compile.
Use the current LTS release, JDK 25, from the official Java site oracle.com/java. The manual needs JDK 11 or later.
Install the JDK first, then the IDE: this course uses Apache NetBeans.
On the next slides, pick your operating system: each slide has direct download links, the steps and a YouTube video link.

Setting up · 2 of 4

Install the JDK

Setting up · 3 of 4

Install Apache NetBeans

Setting up · 4 of 4

Your first project in NetBeans

Theory 1 of 6

From .java to a running program

You write Lab1Demo.java; javac compiles it to bytecode in Lab1Demo.class.
The JVM loads the bytecode and starts at main: “write once, run anywhere”.
A public class must live in a file with the same name.

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Theory 2 of 6

Structure of a Java program

public class Lab1Demo {
    public static void main(String[] args) {
        System.out.println("Hello, Java!");
    }
}

Every statement lives inside a class; execution begins in main.
System.out.println() prints a line to the console.
Check your setup: compile and run this before starting the tasks.

Theory 3 of 6

Variables and the eight primitive types

Type	Holds	Example
byte / short	small integers	`byte b = 100;`
int	common integers	`int age = 21;`
long	large integers (suffix L)	`long pop = 9876543210L;`
float	single-precision (suffix f)	`float gpa = 3.75f;`
double	double-precision decimals	`double h = 5.91;`
char	one character	`char grade = 'A';`
boolean	true / false	`boolean ok = true;`

Java is statically typed: every variable has a declared type. String is a reference type for text.

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Theory 4 of 6

Type casting

Widening (small → large) is automatic and safe.
Narrowing needs a cast and may lose data: the fraction is cut off, not rounded.

Type casting

double d = 25;            // widening: automatic -> 25.0
int price = (int) 99.99;  // narrowing: explicit -> 99

Theory 5 of 6

Decisions: if-else and switch

Use if / else if / else for ranges and conditions.
Use switch to compare one value against fixed cases; forget break and execution falls through.

Decisions: if-else and switch

switch (score / 10) {
    case 10: case 9: grade = 'A'; break;
    case 8:          grade = 'B'; break;
    default:         grade = 'F';
}

Theory 6 of 6

Loops, break and continue

Theory 6 of 6

Loops, break and continue (cont.)

for: number of iterations known in advance (summation).
while: repeat while a condition holds (reverse digits).
do-while: body runs at least once (Collatz sequence).
break leaves the loop; continue skips to the next iteration.

Implementation design

Execution flow

Declare and print the eight primitive variables and a String
Widen an int to double, narrow a double to int, convert char ↔ int
Classify a number (positive/zero/negative) and a BMI with if-else
Assign a letter grade with switch
Sum 1..10 with for; print even numbers using continue and break
Reverse digits with while
Print the Collatz sequence of 27 with do-while

Single class, everything inside main: the focus is syntax, not objects.

Code walkthrough 1 of 10 · Lab1Demo.java

Variables of every primitive type

// 1. Primitive Data Types and String
byte byteVal = 100;
short shortVal = 30000;
int age = 21;
long bigNum = 9876543210L;
float gpa = 3.75f;
double height = 5.91;
char initial = 'A';
boolean isStudent = true;
String name = "Mozdaher Abdul Quader";

One variable per primitive type, plus a String.
Note the suffixes: L for long, f for float.

Code walkthrough 2 of 10 · Lab1Demo.java

Printing with labels

System.out.println("=== Primitive Data Types and String ===");
System.out.println("byte    : " + byteVal);
System.out.println("short   : " + shortVal);
System.out.println("int     : " + age);
System.out.println("long    : " + bigNum);
System.out.println("float   : " + gpa);
System.out.println("double  : " + height);
System.out.println("char    : " + initial + " (Unicode = " + (int) initial + ")");
System.out.println("boolean : " + isStudent);
System.out.println("String  : " + name);

+ joins text and values into one String.
(int) initial shows the Unicode number of a char.

Code walkthrough 3 of 10 · Lab1Demo.java

Widening and narrowing casts

// 2. Type Casting
System.out.println("\n=== Type Casting ===");
double ageAsDouble = age;
System.out.println("int " + age + " widened to double: " + ageAsDouble);

double pi = 3.14159;
int piTruncated = (int) pi;
System.out.println("double " + pi + " narrowed to int: " + piTruncated);

Code walkthrough 3 of 10 · Lab1Demo.java

Widening and narrowing casts (cont.)

char letter = 'Z';
int code = letter;
char nextChar = (char) (code + 1);
System.out.println("char 'Z' as int: " + code + " | next char: " + nextChar);

int → double happens automatically (widening).
double → int needs (int) and drops the fraction.
A char is a number: 90 + 1 is the char after Z.

Code walkthrough 4 of 10 · Lab1Demo.java

if / else if / else

// 3. Conditional Statement
System.out.println("\n=== Conditional Statement ===");
int n = 42;
if (n > 0) {
    System.out.println(n + " is Positive");
} else if (n == 0) {
    System.out.println(n + " is Zero");
} else {
    System.out.println(n + " is Negative");
}

Only the first true branch runs.

Code walkthrough 5 of 10 · Lab1Demo.java

Ranges with an if-else chain

double weightKg = 70.0;
double heightM = 1.75;
double bmi = weightKg / (heightM * heightM);
System.out.printf("BMI = %.2f => ", bmi);
if (bmi < 18.5) {
    System.out.println("Underweight");
} else if (bmi < 25.0) {
    System.out.println("Normal weight");
} else if (bmi < 30.0) {
    System.out.println("Overweight");
} else {
    System.out.println("Obese");
}

Each test only needs the upper bound: earlier branches already ruled out smaller values.
printf("%.2f") prints two decimals.

Code walkthrough 6 of 10 · Lab1Demo.java

switch with fall-through

int score = 85;
char grade;
switch (score / 10) {
    case 10:
    case 9:
        grade = 'A';
        break;
    case 8:
        grade = 'B';
        break;
    case 7:
        grade = 'C';
        break;
    case 6:
        grade = 'D';
        break;
    default:
        grade = 'F';
}

score / 10 is integer division: 85 → 8.
case 10: has no break, so it falls through to case 9.
default catches everything else.

Code walkthrough 7 of 10 · Lab1Demo.java

for loop: summation

// 5. For Loop
System.out.println("\n=== For Loop: Summation 1 to n ===");
int upperBound = 10;
int sum = 0;
for (int i = 1; i <= upperBound; i++) {
    sum = sum + i;
}
System.out.println("Sum of 1 to " + upperBound + " = " + sum);

Initialise, test, update — all in the loop header.

Code walkthrough 8 of 10 · Lab1Demo.java

continue and break

System.out.print("Even numbers from 1 to 20, skipping multiples of 6: ");
for (int i = 1; i <= 20; i++) {
    if (i % 6 == 0) {
        continue;
    }
    if (i > 18) {
        break;
    }
    if (i % 2 == 0) {
        System.out.print(i + " ");
    }
}
System.out.println();

continue skips multiples of 6.
break stops the loop once i passes 18.

Code walkthrough 9 of 10 · Lab1Demo.java

while loop: reverse the digits

// 6. While Loop
System.out.println("\n=== While Loop: Reverse Digits ===");
int number = 12345;
int temp = number;
int reversed = 0;
while (temp != 0) {
    int digit = temp % 10;
    reversed = reversed * 10 + digit;
    temp = temp / 10;
}
System.out.println("Original number: " + number);
System.out.println("Reversed number: " + reversed);

% 10 takes the last digit; / 10 removes it.
The loop runs until no digits are left.

Code walkthrough 10 of 10 · Lab1Demo.java

do-while: the Collatz sequence

// 7. Do-While Loop
System.out.println("\n=== Do-While Loop: Collatz Sequence ===");
long collatz = 27;
int steps = 0;
System.out.print("Sequence: ");
do {
    System.out.print(collatz + " ");
    if (collatz % 2 == 0) {
        collatz = collatz / 2;
    } else {

Code walkthrough 10 of 10 · Lab1Demo.java

do-while: the Collatz sequence (cont.)

        collatz = 3 * collatz + 1;
    }
    steps++;
} while (collatz != 1);
System.out.println("1");
System.out.println("Steps to reach 1: " + steps);

The body runs before the test, so 27 is printed first.
Even → halve; odd → 3n + 1; stop at 1.

Step through the code · 1 of 3

Trace: widening and narrowing

Watch each variable appear in main’s stack frame and see exactly what a cast keeps.

Step through the code · 1 of 3

Trace: widening and narrowing (cont.)

Step through the code · 2 of 3

Trace: reversing the digits

Follow temp, digit and reversed through every pass of the while loop.

Step through the code · 2 of 3

Trace: reversing the digits (cont.)

Step through the code · 3 of 3

Trace: switch, case by case

Pick a score. See which case the switch jumps to, how 100 falls through into case 9, and what break does.

Step through the code · 3 of 3

Trace: switch, case by case (cont.)

For reference · 1 file

The complete program

public class Lab1Demo {
    public static void main(String[] args) {

        // 1. Primitive Data Types and String
        byte byteVal = 100;
        short shortVal = 30000;
        int age = 21;
        long bigNum = 9876543210L;
        float gpa = 3.75f;
        double height = 5.91;
        char initial = 'A';
        boolean isStudent = true;
        String name = "Mozdaher Abdul Quader";

        System.out.println("=== Primitive Data Types and String ===");
        System.out.println("byte    : " + byteVal);
        System.out.println("short   : " + shortVal);
        System.out.println("int     : " + age);
        System.out.println("long    : " + bigNum);
        System.out.println("float   : " + gpa);
        System.out.println("double  : " + height);
        System.out.println("char    : " + initial + " (Unicode = " + (int) initial + ")");
        System.out.println("boolean : " + isStudent);
        System.out.println("String  : " + name);

        // 2. Type Casting
        System.out.println("\n=== Type Casting ===");
        double ageAsDouble = age;
        System.out.println("int " + age + " widened to double: " + ageAsDouble);

        double pi = 3.14159;
        int piTruncated = (int) pi;
        System.out.println("double " + pi + " narrowed to int: " + piTruncated);

        char letter = 'Z';
        int code = letter;
        char nextChar = (char) (code + 1);
        System.out.println("char 'Z' as int: " + code + " | next char: " + nextChar);

        // 3. Conditional Statement
        System.out.println("\n=== Conditional Statement ===");
        int n = 42;
        if (n > 0) {
            System.out.println(n + " is Positive");
        } else if (n == 0) {
            System.out.println(n + " is Zero");
        } else {
            System.out.println(n + " is Negative");
        }

        double weightKg = 70.0;
        double heightM = 1.75;
        double bmi = weightKg / (heightM * heightM);
        System.out.printf("BMI = %.2f => ", bmi);
        if (bmi < 18.5) {
            System.out.println("Underweight");
        } else if (bmi < 25.0) {
            System.out.println("Normal weight");
        } else if (bmi < 30.0) {
            System.out.println("Overweight");
        } else {
            System.out.println("Obese");
        }

        // 4. Switch Statement
        System.out.println("\n=== Switch Statement: Grade Classifier ===");
        int score = 85;
        char grade;
        switch (score / 10) {
            case 10:
            case 9:
                grade = 'A';
                break;
            case 8:
                grade = 'B';
                break;
            case 7:
                grade = 'C';
                break;
            case 6:
                grade = 'D';
                break;
            default:
                grade = 'F';
        }
        System.out.println("Score: " + score + " => Grade: " + grade);

        // 5. For Loop
        System.out.println("\n=== For Loop: Summation 1 to n ===");
        int upperBound = 10;
        int sum = 0;
        for (int i = 1; i <= upperBound; i++) {
            sum = sum + i;
        }
        System.out.println("Sum of 1 to " + upperBound + " = " + sum);

        System.out.print("Even numbers from 1 to 20, skipping multiples of 6: ");
        for (int i = 1; i <= 20; i++) {
            if (i % 6 == 0) {
                continue;
            }
            if (i > 18) {
                break;
            }
            if (i % 2 == 0) {
                System.out.print(i + " ");
            }
        }
        System.out.println();

        // 6. While Loop
        System.out.println("\n=== While Loop: Reverse Digits ===");
        int number = 12345;
        int temp = number;
        int reversed = 0;
        while (temp != 0) {
            int digit = temp % 10;
            reversed = reversed * 10 + digit;
            temp = temp / 10;
        }
        System.out.println("Original number: " + number);
        System.out.println("Reversed number: " + reversed);

        // 7. Do-While Loop
        System.out.println("\n=== Do-While Loop: Collatz Sequence ===");
        long collatz = 27;
        int steps = 0;
        System.out.print("Sequence: ");
        do {
            System.out.print(collatz + " ");
            if (collatz % 2 == 0) {
                collatz = collatz / 2;
            } else {
                collatz = 3 * collatz + 1;
            }
            steps++;
        } while (collatz != 1);
        System.out.println("1");
        System.out.println("Steps to reach 1: " + steps);
    }
}

Copy or download each file, save it under the same name, then compile and run: javac *.java → java Lab1Demo

Implementation

Expected output

=== Primitive Data Types and String ===
byte    : 100
short   : 30000
int     : 21
long    : 9876543210
float   : 3.75
double  : 5.91
char    : A (Unicode = 65)
boolean : true
String  : Mozdaher Abdul Quader

=== Type Casting ===
int 21 widened to double: 21.0
double 3.14159 narrowed to int: 3
char 'Z' as int: 90 | next char: [

=== Conditional Statement ===
42 is Positive
BMI = 22.86 => Normal weight

=== Switch Statement: Grade Classifier ===
Score: 85 => Grade: B

=== For Loop: Summation 1 to n ===
Sum of 1 to 10 = 55
Even numbers from 1 to 20, skipping multiples of 6: 2 4 8 10 14 16 18

=== While Loop: Reverse Digits ===
Original number: 12345
Reversed number: 54321

=== Do-While Loop: Collatz Sequence ===
Sequence: 27 82 41 124 62 31 94 47 142 71 214 107 322 161 484 242 121 364 182 91 274 137 412 206 103 310 155 466 233 700 350 175 526 263 790 395 1186 593 1780 890 445 1336 668 334 167 502 251 754 377 1132 566 283 850 425 1276 638 319 958 479 1438 719 2158 1079 3238 1619 4858 2429 7288 3644 1822 911 2734 1367 4102 2051 6154 3077 9232 4616 2308 1154 577 1732 866 433 1300 650 325 976 488 244 122 61 184 92 46 23 70 35 106 53 160 80 40 20 10 5 16 8 4 2 1
Steps to reach 1: 111

Why is the next char after Z a “[”? Characters are numbers: 'Z' is 90, and 91 is '['.

Interactive 1 of 5

Try widening and narrowing

Interactive 2 of 5

Evaluate operators step by step

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Interactive 3 of 5

Follow an if-else ladder

Interactive 4 of 5

Watch switch and fall-through

Interactive 5 of 5

Compare the three loops

In-lab task 1 of 4

Task 1: Temperature converter

Read a temperature in Celsius and convert it to Fahrenheit, Kelvin and Rankine: F = C × 1.8 + 32, K = C + 273.15, R = F + 459.67.

Requirements

Use double variables for all temperatures
Print every converted value with a clear label
Use meaningful variable names

Show a hint

Read with Scanner sc = new Scanner(System.in); double c = sc.nextDouble(); and compute F first, because R depends on it.

In-lab task 2 of 4

Task 2: FizzBuzz extended

Print 1 to 50: FizzBuzz if divisible by 3 and 5, Fizz for 3, Buzz for 5, Boom for 7, otherwise the number.

Requirements

Use a for loop
Use if / else if / else
Test “3 and 5” before 3 or 5 alone

Show a hint

Order matters: once one branch of an if-else chain matches, the rest are skipped. Use i % 15 == 0 or i % 3 == 0 && i % 5 == 0 first.

In-lab task 3 of 4

Task 3: Number system classifier

Read an integer and classify it by the remainder when divided by 4: 0 → Divisible by 4, 1 or 3 → Odd, 2 → Even, not divisible by 4.

Requirements

Read input with Scanner
Use a traditional switch
Print the number and its classification

Show a hint

case 1: case 3: can share one body. Careful with negative numbers: -3 % 4 is -3 in Java.

In-lab task 4 of 4

Task 4: Digit frequency counter

Read a positive integer and count how often each digit 0–9 appears.

Requirements

Repeat input with do-while until the number is positive
Store counts in an int[10]
Extract digits with a while loop
Print the frequency of each digit

Show a hint

Inside the loop: freq[n % 10]++; n /= 10;. Use long if you want very large inputs.

In-lab tasks

Show your work during the lab

For each task, show the instructor:

the source code
a successful compilation
the running output
a short explanation of the logic you used

Lab report · exercise 1 of 2

Student grade management system

Manage the marks of five students in Mathematics, Physics and Chemistry.

Requirements

Store the marks of 5 students × 3 subjects in arrays
Compute each student’s average with loops
Assign grades with if-else: ≥80 A, ≥70 B, ≥60 C, ≥50 D, else F
Find and print the highest and lowest scorer
Print a motivational message per grade using switch
Display the results in a clear table

Lab report · exercise 2 of 2

Pattern & sequence explorer

A menu-driven program: 1. Pascal’s triangle, 2. Primes by the Sieve of Eratosthenes, 3. Perfect numbers up to 10000, 4. Exit.

Requirements

Lab report

Writing the lab report

Problem statement and your design (classes, fields, methods)
Complete source code, formatted and commented
Sample output or screenshots for normal and edge cases
A short discussion: what each OOP concept did in your program

Academic integrity

Copying from the internet, classmates, seniors or any other unauthorized source is strictly prohibited. Full marks may be deducted if plagiarism, copied work or academic dishonesty is detected. Complete the tasks, implementation, output analysis and report yourself.

Discussion and analysis

Viva questions (1 of 2)

Why is Java called statically typed, and how does that help?

Show the answer

Every variable must be declared with a type before use, so the compiler catches type errors (for example assigning 3.7 to an int without a cast) before the program runs.

What does (int) 99.99 give, and why must the cast be written?

Show the answer

99. Narrowing can lose data (the fraction is truncated), so Java makes you state it explicitly.

Discussion and analysis

Viva questions (2 of 2)

When would you choose do-while over while?

Show the answer

When the body must run at least once, such as showing a menu or the first value of the Collatz sequence.

What happens if you remove a break from a switch case?

Show the answer

Execution falls through into the next case and runs its statements too, until a break or the end of the switch.

Check yourself

Quiz

Summary

javac turns .java source into .class bytecode; the JVM runs it starting from main.
Eight primitive types plus String; Java checks types at compile time.
Widening is automatic; narrowing needs a cast and can lose data.
if-else for conditions and ranges, switch for fixed values (remember break).
for when the count is known, while for conditions, do-while to run at least once.

Next: Lab 2 · Classes and objects All labs

Java Syntax, Data Types & Control Flow

Why this lab

Lab at a glance

After this lab you can

Before you start

Plan for the session

Contents

Which Java do you need?

Install the JDK

Install Apache NetBeans

Your first project in NetBeans

From .java to a running program

Structure of a Java program

Variables and the eight primitive types

Type casting

Type casting

Decisions: if-else and switch

Decisions: if-else and switch

Loops, break and continue

Loops, break and continue (cont.)

Execution flow

Variables of every primitive type

Printing with labels

Widening and narrowing casts

Widening and narrowing casts (cont.)

if / else if / else

Ranges with an if-else chain

switch with fall-through

for loop: summation

continue and break

while loop: reverse the digits

do-while: the Collatz sequence

do-while: the Collatz sequence (cont.)

Trace: widening and narrowing

Trace: widening and narrowing (cont.)

Trace: reversing the digits

Trace: reversing the digits (cont.)

Trace: switch, case by case

Trace: switch, case by case (cont.)

The complete program

Expected output

Try widening and narrowing

Evaluate operators step by step

Follow an if-else ladder

Watch switch and fall-through

Compare the three loops

Task 1: Temperature converter

Task 2: FizzBuzz extended

Task 3: Number system classifier

Task 4: Digit frequency counter

Show your work during the lab

Student grade management system

Pattern & sequence explorer

Writing the lab report

Academic integrity

Viva questions (1 of 2)

Viva questions (2 of 2)

Quiz

Summary