Primitive data types in Java - Mini Project: Build & Apply

Primitive Data Types in Java

📖 Scenario: You are creating a simple Java program to store and display basic information about a product using primitive data types.

🎯 Goal: Build a Java program that declares variables with primitive data types, assigns values, and prints them.

📋 What You'll Learn

Declare variables using Java primitive data types: int, double, char, and boolean

Assign specific values to each variable

Print the values to the console

💡 Why This Matters

🌍 Real World

Primitive data types are used to store simple data like numbers, letters, and true/false values in many programs.

💼 Career

Understanding primitive data types is essential for any Java developer to handle data efficiently and write clear code.

1

Declare primitive variables

Declare a variable called productId of type int and set it to 101.

Java

// Declare an int variable named productId and assign 101
// Your code here

Hint

Use int for whole numbers like IDs.

2

Add more primitive variables

Declare a variable called price of type double and set it to 29.99. Also declare a variable called inStock of type boolean and set it to true.

Java

int productId = 101;
// Declare a double variable named price and assign 29.99
// Declare a boolean variable named inStock and assign true
// Your code here

Hint

Use double for decimal numbers and boolean for true/false values.

3

Add a character variable

Declare a variable called category of type char and set it to the letter 'E'.

Java

int productId = 101;
double price = 29.99;
boolean inStock = true;
// Declare a char variable named category and assign 'E'
// Your code here

Hint

Use single quotes ' ' for char values.

4

Print all variables

Use System.out.println to print the values of productId, price, inStock, and category each on a new line.

Java

int productId = 101;
double price = 29.99;
boolean inStock = true;
char category = 'E';
// Print productId, price, inStock, and category each on a new line
// Your code here

Hint

Use separate System.out.println statements for each variable.

Practice

1. Which of the following is NOT a primitive data type in Java?

easy

A. char

B. boolean

C. int

D. String

Solution

1. Step 1: Recall Java primitive types

   Java primitive types include int, boolean, char, byte, short, long, float, and double.

2. Step 2: Identify non-primitive type

   String is a class in Java, not a primitive type.

3. Final Answer:

   String -> Option D

4. Quick Check:

   Primitive types exclude classes like String [OK]

Hint: Remember primitives are simple types, not objects like String [OK]

Common Mistakes:

• Confusing String as primitive
• Thinking boolean is not primitive
• Mixing wrapper classes with primitives

2. Which of the following is the correct way to declare a variable of type byte in Java?

easy

A. byte b = 127;

B. byte b = 128;

C. byte b = 'a';

D. byte b = 128L;

Solution

1. Step 1: Understand byte range

   byte stores values from -128 to 127 inclusive.

2. Step 2: Check each option

   byte b = 128; uses 128 which is out of range; byte b = 127; uses 127 which is valid; byte b = 'a'; assigns a char which is not directly compatible; byte b = 128L; uses long literal 128L which is invalid for byte.

3. Final Answer:

   byte b = 127; -> Option A

4. Quick Check:

   byte max value = 127 [OK]

Hint: byte max is 127, so use values within -128 to 127 [OK]

Common Mistakes:

• Assigning values outside byte range
• Using char or long literals directly
• Not knowing byte limits

3. What is the output of the following Java code?

int x = 5;
float y = 2.0f;
System.out.println(x + y);

medium

A. 7.0

B. 7.0f

C. 7

D. 7.0d

Solution

1. Step 1: Understand type promotion in expression

   int x is promoted to float when added to float y.

2. Step 2: Calculate the sum and output type

   5 + 2.0f = 7.0 (float), but println prints float as decimal number without suffix.

3. Final Answer:

   7.0 -> Option A

4. Quick Check:

   int + float = float output 7.0 [OK]

Hint: int + float results in float decimal output [OK]

Common Mistakes:

• Expecting integer output
• Confusing float suffix in output
• Ignoring type promotion rules

4. Identify the error in the following Java code snippet:

char c = 'AB';

medium

A. char cannot be assigned a value directly

B. Missing semicolon at end

C. char can only hold a single character

D. char must be initialized with a number

Solution

1. Step 1: Check char assignment rules

   char stores a single 16-bit Unicode character, so it must be assigned a single character in single quotes.

2. Step 2: Analyze the given code

   'AB' is two characters, which is invalid for char type.

3. Final Answer:

   char can only hold a single character -> Option C

4. Quick Check:

   char = single character only [OK]

Hint: char holds exactly one character in single quotes [OK]

Common Mistakes:

• Assigning multiple characters to char
• Confusing char with String
• Forgetting single quotes for char

5. You want to store a large whole number that is bigger than int can hold. Which primitive type should you use in Java?

hard

A. short

B. long

C. float

D. double

Solution

1. Step 1: Recall int and long ranges

   int holds up to about 2 billion (2^31-1), long holds much larger values (2^63-1).

2. Step 2: Choose type for large whole number

   long is the correct primitive type for large integers beyond int range; float and double are for decimals, short is smaller than int.

3. Final Answer:

   long -> Option B

4. Quick Check:

   Use long for large integers beyond int [OK]

Hint: Use long for big whole numbers beyond int range [OK]

Common Mistakes:

• Using float/double for whole numbers
• Choosing short which is smaller
• Not knowing long size