Static methods in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of static method call

What is the output of the following Java program?

Java

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

A 2

B 0

C 1

D Compilation error

💡 Hint

Static methods can access static variables directly.

The static method increment() increases the static variable count by 1 each time it is called. It is called twice, so count becomes 2.

🧠 Conceptual

intermediate

Static method access to instance variables

Which statement about static methods in Java is true?

A Static methods can only access static variables directly.

B Static methods can directly access instance variables without an object.

C Static methods can access instance variables if they are declared final.

D Static methods can access instance variables only if the class is final.

💡 Hint

Think about what static means in relation to objects.

Static methods belong to the class, not to any object instance, so they cannot access instance variables directly. They can only access static variables directly.

🔧 Debug

advanced

Identify the error in static method usage

What error will this code produce?

Java

public class Example {
    int number = 5;
    public static void printNumber() {
        System.out.println(number);
    }
    public static void main(String[] args) {
        printNumber();
    }
}

A Output: 5

B Runtime error: NullPointerException

C Compilation error: non-static variable number cannot be referenced from a static context

D Compilation error: missing return statement

💡 Hint

Static methods cannot access instance variables directly.

The static method printNumber() tries to access the instance variable number without an object reference, which causes a compilation error.

❓ Predict Output

advanced

Output of static method with parameters

What is the output of this Java program?

Java

public class Calculator {
    public static int multiply(int a, int b) {
        return a * b;
    }
    public static void main(String[] args) {
        int result = multiply(3, 4);
        System.out.println(result);
    }
}

A Compilation error

B 7

C 34

D 12

💡 Hint

Static methods can take parameters and return values.

The static method multiply returns the product of 3 and 4, which is 12.

🚀 Application

expert

Static method call from instance method

Consider this Java class. What will be the output when main runs?

Java

public class Counter {
    private static int count = 0;
    public void increment() {
        count++;
    }
    public static void printCount() {
        System.out.println(count);
    }
    public static void main(String[] args) {
        Counter c1 = new Counter();
        Counter c2 = new Counter();
        c1.increment();
        c2.increment();
        printCount();
    }
}

A Compilation error

B 2

C 1

D 0

💡 Hint

Static variables are shared across all instances.

Both c1 and c2 increment the same static variable count, so after two increments, count is 2.

Practice

1. Which statement about static methods in Java is true?

easy

A. Static methods belong to the class and can be called without creating an object.

B. Static methods can only be called on objects of the class.

C. Static methods can access instance variables directly.

D. Static methods must always return void.

Solution

1. Step 1: Understand what static means

   Static methods belong to the class itself, not to any object instance.

2. Step 2: Check method calling rules

   Static methods can be called using the class name without creating an object.

3. Final Answer:

   Static methods belong to the class and can be called without creating an object. -> Option A

4. Quick Check:

   Static method = class method call [OK]

Hint: Static methods use class name, no object needed [OK]

Common Mistakes:

• Thinking static methods need an object to call
• Assuming static methods access instance variables
• Believing static methods must return void

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

easy

A. public void static myMethod() {}

B. static void public myMethod() {}

C. public static void myMethod() {}

D. void static public myMethod() {}

Solution

1. Step 1: Recall Java method declaration order

   In Java, the correct order is access modifier, then static keyword, then return type, then method name.

2. Step 2: Match the correct syntax

   public static void myMethod() {} follows this order: public static void myMethod() {}.

3. Final Answer:

   public static void myMethod() {} -> Option C

4. Quick Check:

   Access + static + return type = correct order [OK]

Hint: Remember: access modifier before static keyword [OK]

Common Mistakes:

• Placing static after return type
• Omitting access modifier
• Mixing order of keywords

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

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

medium

A. 2

B. 1

C. Compilation error

D. 0

Solution

1. Step 1: Understand static variable and method behavior

   The static variable count starts at 0 and is shared by all calls.

2. Step 2: Trace method calls

   Each call to increment() increases count by 1. Called twice, count becomes 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Two increments = count 2 [OK]

Hint: Static variables keep value across static method calls [OK]

Common Mistakes:

• Thinking count resets each call
• Confusing static and instance variables
• Expecting compilation error due to static usage

4. Identify the error in the following code snippet:

public class Example {
    int x = 5;
    static void printX() {
        System.out.println(x);
    }
}

medium

A. Missing return type for printX method.

B. Cannot use instance variable x inside static method printX.

C. Static methods cannot have print statements.

D. Class Example must be declared static.

Solution

1. Step 1: Check static method access rules

   Static methods cannot access instance variables directly because they belong to the class, not an object.

2. Step 2: Identify the error in code

   Method printX() tries to print instance variable x without an object, causing an error.

3. Final Answer:

   Cannot use instance variable x inside static method printX. -> Option B

4. Quick Check:

   Static method can't access instance variables directly [OK]

Hint: Static methods can't use instance variables directly [OK]

Common Mistakes:

• Assuming static methods can access instance variables
• Thinking static methods need return type fix
• Believing classes must be static

5. You want to create a utility class MathUtils with a static method square(int n) that returns the square of a number. Which implementation is correct?

hard

A. public class MathUtils { public int square(int n) { return n * n; } }

B. public class MathUtils { static void square(int n) { return n * n; } }

C. public static class MathUtils { public int square(int n) { return n * n; } }

D. public class MathUtils { public static int square(int n) { return n * n; } }

Solution

1. Step 1: Identify static method requirements

   The method should be static to call without creating an object.

2. Step 2: Check method signature and return type

   Method must return int and be declared static with proper access modifier.

3. Step 3: Validate options

   public class MathUtils { public static int square(int n) { return n * n; } } correctly declares a public static method returning int.

4. Final Answer:

   public class MathUtils { public static int square(int n) { return n * n; } } -> Option D

5. Quick Check:

   Static method with return type and public access [OK]

Hint: Utility methods should be static with correct return type [OK]

Common Mistakes:

• Omitting static keyword
• Using void return type when returning value
• Declaring class static incorrectly