Primitive data types in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable of type int.

Java

int number = [1];

Drag options to blanks, or click blank then click option'

Atrue

B"10"

C10.5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers, which makes them strings.

Assigning decimal numbers to int variables.

The variable number is declared as an int, so it must be assigned an integer value like 10.

2fill in blank

medium

Complete the code to declare a variable of type boolean.

Java

boolean isJavaFun = [1];

Drag options to blanks, or click blank then click option'

A"true"

B1

Ctrue

Dyes

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around true or false, making them strings.

Using numbers like 1 or 0 instead of boolean literals.

The boolean type accepts only true or false without quotes.

3fill in blank

hard

Fix the error in the code to correctly declare a double variable.

Java

double price = [1];

Drag options to blanks, or click blank then click option'

A15.0

B15,0

C15

D"15.0"

Attempts:

3 left

💡 Hint

Common Mistakes

Using commas instead of dots for decimals.

Putting the number inside quotes, making it a string.

The double type requires a decimal number without quotes and with a dot as decimal separator.

4fill in blank

hard

Fill both blanks to declare a char variable and assign a letter.

Java

char letter = [1][2];

Drag options to blanks, or click blank then click option'

A"A"

B'A'

C'B'

D"B"

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes instead of single quotes for chars.

Leaving the character unquoted.

The char type holds a single character enclosed in single quotes. The second blank is empty because the character literal is complete.

5fill in blank

hard

Fill all three blanks to declare variables of types int, float, and boolean.

Java

int count = [1];
float temperature = [2]f;
boolean isActive = [3];

Drag options to blanks, or click blank then click option'

A100

B36.6

Ctrue

D"true"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around boolean values.

Omitting the 'f' suffix for float literals.

Assigning decimal numbers to int variables.

The int variable count needs an integer like 100.
The float variable temperature needs a decimal number with an 'f' suffix.
The boolean variable isActive needs the literal true or false without quotes.

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