Static variables in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a static variable named count.

Java

public class Counter {
    public static [1] count = 0;
}

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

Afinal

Bstatic

Cvoid

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' as a variable type.

Forgetting to specify the variable type.

The keyword int declares the variable type. The static keyword is already present.

2fill in blank

medium

Complete the code to access the static variable count from the class Counter.

Java

int currentCount = Counter.[1];

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

Acount

BgetCount()

Cthis.count

DCounter()

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call count as a method.

Using 'this' keyword to access static variables.

Static variables are accessed using the class name followed by a dot and the variable name.

3fill in blank

hard

Fix the error in the code to correctly increment the static variable count.

Java

public class Counter {
    public static int count = 0;
    public void increment() {
        [1]++;
    }
}

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

ACounter.count

Bcount

Cthis.count

Dincrement

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this.count' which is incorrect for static variables.

Trying to increment a method name.

Inside instance methods, static variables should be accessed with the class name to avoid confusion.

4fill in blank

hard

Fill both blanks to create a static method that returns the static variable count.

Java

public class Counter {
    private static int count = 0;
    public static [1] getCount() {
        return [2];
    }
}

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

Aint

Bcount

Cthis.count

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' as return type when a value is returned.

Trying to use 'this.count' inside a static method.

The method must return an integer, so its return type is int. The static variable count is returned directly by name.

5fill in blank

hard

Fill all three blanks to create a class with a static variable, a constructor that increments it, and a static method to get its value.

Java

public class [1] {
    private static int count = 0;
    public [2]() {
        [3]++;
    }
    public static int getCount() {
        return count;
    }
}

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

ACounter

CCounter.count

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for class and constructor.

Incrementing the variable without the class name inside the constructor.

The class name is Counter. The constructor has the same name as the class. The static variable is incremented using Counter.count.

Practice

1. What is a key characteristic of a static variable in Java?

easy

A. It belongs to the class and is shared by all instances.

B. It is unique to each object created from the class.

C. It can only be accessed inside instance methods.

D. It is automatically deleted when an object is destroyed.

Solution

1. Step 1: Understand static variable ownership

   A static variable belongs to the class itself, not to any individual object.

2. Step 2: Recognize sharing behavior

   Because it belongs to the class, all objects share the same static variable value.

3. Final Answer:

   It belongs to the class and is shared by all instances. -> Option A

4. Quick Check:

   Static variable = shared by all objects [OK]

Hint: Static means shared by class, not per object [OK]

Common Mistakes:

• Thinking static variables are unique per object
• Confusing static with instance variables
• Assuming static variables are deleted with objects

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

easy

A. static int count;

B. int static count;

C. int count static;

D. count static int;

Solution

1. Step 1: Recall Java syntax for static variables

   The keyword static comes before the type when declaring a static variable.

2. Step 2: Check each option

   Only static int count; follows the correct syntax.

3. Final Answer:

   static int count; -> Option A

4. Quick Check:

   static keyword before type = correct syntax [OK]

Hint: Put 'static' before the type when declaring [OK]

Common Mistakes:

• Placing static after the variable name
• Mixing order of keywords
• Using invalid syntax order

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

class Test {
    static int count = 0;
    Test() {
        count++;
    }
    public static void main(String[] args) {
        new Test();
        new Test();
        System.out.println(Test.count);
    }
}

medium

A. Compilation error

B. 1

C. 0

D. 2

Solution

1. Step 1: Understand static variable incrementation

   Each time a new Test object is created, the constructor increments count by 1.

2. Step 2: Count the number of objects created

   Two objects are created, so count becomes 2.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Two objects increment count twice = 2 [OK]

Hint: Static count increments with each new object [OK]

Common Mistakes:

• Assuming count resets for each object
• Confusing instance and static variables
• Expecting compilation error due to static usage

4. Identify the error in the following code snippet:

class Counter {
    static int count;
    void increment() {
        count++;
    }
    public static void main(String[] args) {
        Counter c = new Counter();
        c.increment();
        System.out.println(count);
    }
}

medium

A. Cannot access static variable from instance method.

B. No error; code runs and prints 1.

C. Cannot access static variable directly in static method without class name.

D. Static variable count is not initialized.

Solution

1. Step 1: Check static variable initialization

   Static int variables default to 0 if not explicitly initialized.

2. Step 2: Verify method calls and access

   The instance method increment() correctly increments the static variable. The static method main accesses count directly, which is allowed.

3. Final Answer:

   No error; code runs and prints 1. -> Option B

4. Quick Check:

   Static variable accessible and increments correctly [OK]

Hint: Static vars default to 0; accessible in static main [OK]

Common Mistakes:

• Thinking static vars must be explicitly initialized
• Assuming static vars can't be accessed without class name inside same class
• Confusing instance and static method access rules

5. Consider this Java class:

class Employee {
    static int employeeCount = 0;
    String name;
    Employee(String name) {
        this.name = name;
        employeeCount++;
    }
    static void printCount() {
        System.out.println("Total employees: " + employeeCount);
    }
}

public class Main {
    public static void main(String[] args) {
        Employee e1 = new Employee("Alice");
        Employee e2 = new Employee("Bob");
        e1.printCount();
        Employee.printCount();
    }
}

What will be the output when running Main?

hard

A. Total employees: 1
Total employees: 2

B. Total employees: 2
Total employees: 1

C. Total employees: 2
Total employees: 2

D. Compilation error due to calling static method on instance

Solution

1. Step 1: Count employees created

   Two Employee objects are created, so employeeCount becomes 2.

2. Step 2: Understand static method calls

   Calling printCount() on instance e1 or class Employee both print the same static variable value.

3. Final Answer:

   Total employees: 2 Total employees: 2 -> Option C

4. Quick Check:

   Static method prints shared count = 2 [OK]

Hint: Static method prints shared count; instance call allowed [OK]

Common Mistakes:

• Thinking static method can't be called on instance
• Assuming employeeCount resets per object
• Confusing output order or values