Variable declaration and initialization in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an integer variable named age.

Java

int [1];

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

Aage

Bnumber

Ccount

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name different from the one requested.

Forgetting the semicolon at the end (not tested here).

The variable name age is used to declare the integer variable as requested.

2fill in blank

medium

Complete the code to initialize the integer variable score with the value 100.

Java

int score = [1];

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

A10

B1

C100

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different number than 100.

Forgetting the semicolon at the end.

The variable score is initialized with the value 100 as requested.

3fill in blank

hard

Fix the error in the code by completing the variable declaration for a double named price.

Java

double [1] = 9.99;

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

Aprice

Bcost

Camount

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than price.

Misspelling the variable name.

The variable name must be price to match the declaration and initialization.

4fill in blank

hard

Fill both blanks to declare and initialize a boolean variable named isActive with the value true.

Java

[1] [2] = true;

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

Aboolean

Bint

CisActive

Dactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong type like int.

Using a different variable name.

The type is boolean and the variable name is isActive as requested.

5fill in blank

hard

Fill all three blanks to declare and initialize a String variable named name with the value "Alice".

Java

[1] [2] = [3];

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

AString

Bname

C"Alice"

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong type like int.

Forgetting the quotes around the string value.

Using a different variable name.

The type is String, the variable name is name, and the value is the string "Alice".

Practice

1. Which of the following is a correct way to declare and initialize an integer variable named age with the value 25 in Java?

easy

A. int age = 25;

B. int age;

C. age = 25;

D. int 25 = age;

Solution

1. Step 1: Understand variable declaration and initialization

   Declaring a variable means telling the computer the type and name. Initializing means giving it a value.

2. Step 2: Check each option for correct syntax

   int age = 25; declares int age and sets it to 25 correctly. int age; declares but does not initialize. age = 25; tries to assign without declaration. int 25 = age; uses invalid syntax.

3. Final Answer:

   int age = 25; -> Option A

4. Quick Check:

   Declaration + initialization = int age = 25; [OK]

Hint: Declare type, name, then assign value with = [OK]

Common Mistakes:

• Forgetting the data type before the variable name
• Assigning a value without declaring the variable first
• Using numbers as variable names

2. Which of the following lines of code will cause a syntax error in Java?

easy

A. double price = 19.99;

B. String name = "John";

C. int 1stNumber = 10;

D. boolean isActive = true;

Solution

1. Step 1: Review Java variable naming rules

   Variable names cannot start with a digit. They must start with a letter, underscore, or dollar sign.

2. Step 2: Check each option for naming errors

   int 1stNumber = 10; uses 1stNumber which starts with a digit, causing a syntax error. Others are valid declarations.

3. Final Answer:

   int 1stNumber = 10; -> Option C

4. Quick Check:

   Variable names cannot start with digits [OK]

Hint: Variable names cannot start with numbers [OK]

Common Mistakes:

• Starting variable names with digits
• Using spaces in variable names
• Missing semicolon at the end

3. What will be the output of the following Java code?

int x = 5;
int y = x + 10;
System.out.println(y);

medium

A. 15

B. 10

C. 5

D. Syntax Error

Solution

1. Step 1: Understand variable initialization and addition

   Variable x is set to 5. Variable y is set to x + 10, which is 5 + 10 = 15.

2. Step 2: Determine the printed value

   The System.out.println(y); prints the value of y, which is 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add values after initialization to find output [OK]

Common Mistakes:

• Confusing variable names
• Forgetting to initialize variables before use
• Assuming output is the first variable's value

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

int number;
number = "10";
System.out.println(number);

medium

A. Variable number is not declared

B. Print statement syntax is incorrect

C. Missing semicolon after declaration

D. Cannot assign a String to an int variable

Solution

1. Step 1: Check variable declaration and assignment types

   The variable number is declared as int, which means it can only hold integer values.

2. Step 2: Identify type mismatch in assignment

   Assigning "10" (a String) to an int variable causes a type mismatch error.

3. Final Answer:

   Cannot assign a String to an int variable -> Option D

4. Quick Check:

   int variables accept only integers [OK]

Hint: Match variable type with assigned value type [OK]

Common Mistakes:

• Assigning text (String) to number variables
• Forgetting to use quotes for Strings
• Confusing variable declaration and assignment

5. You want to declare and initialize three variables in one line: an integer count with 10, a double price with 5.5, and a boolean available with true. Which of the following is the correct way to do this in Java?

hard

A. int count = 10, double price = 5.5, boolean available = true;

B. int count = 10; double price = 5.5; boolean available = true;

C. int count = 10; double price = 5.5, boolean available = true;

D. int count = 10, price = 5.5, available = true;

Solution

1. Step 1: Understand variable declaration rules for different types

   In Java, variables of different types must be declared separately with their own type keyword.

2. Step 2: Analyze each option's syntax

   int count = 10, double price = 5.5, boolean available = true; tries to declare different types separated by commas in one statement, which is invalid. int count = 10; double price = 5.5; boolean available = true; declares each variable with its type and ends each statement with a semicolon, which is correct. int count = 10; double price = 5.5, boolean available = true; mixes semicolon and comma incorrectly. int count = 10, price = 5.5, available = true; declares all variables with one type keyword, which is invalid for different types.

3. Final Answer:

   int count = 10; double price = 5.5; boolean available = true; -> Option B

4. Quick Check:

   Different types need separate declarations [OK]

Hint: Declare each type separately with semicolons [OK]

Common Mistakes:

• Trying to declare different types in one statement with commas
• Missing semicolons between statements
• Assuming one type keyword covers all variables