Static methods in Java - Mini Project: Build & Apply

Using Static Methods in Java

📖 Scenario: You are creating a simple calculator program that can add and multiply numbers. To keep things organized, you want to use static methods inside a class so you can call them without creating an object.

🎯 Goal: Build a Java class called Calculator with two static methods: add and multiply. Then call these methods from the main method to show the results.

📋 What You'll Learn

Create a class named Calculator

Add a static method add that takes two int parameters and returns their sum

Add a static method multiply that takes two int parameters and returns their product

In the main method, call Calculator.add and Calculator.multiply with the numbers 5 and 7

Print the results of both method calls

💡 Why This Matters

🌍 Real World

Static methods are used for utility functions like math calculations, formatting, or helper methods that don't need object data.

💼 Career

Understanding static methods is important for writing clean, reusable code and is commonly used in Java programming jobs.

1

Create the Calculator class

Create a public class called Calculator with an empty body.

Java

public class Calculator {
    // Your code here
}

Hint

Use the class keyword followed by the class name Calculator.

2

Add static methods add and multiply

Inside the Calculator class, add two public static methods: add and multiply. Both take two int parameters named a and b. add returns the sum of a and b. multiply returns the product of a and b.

Java

public class Calculator {
    // Add public static int add(int a, int b) method
    // Add public static int multiply(int a, int b) method
    // Your code here
}

Hint

Static methods use the static keyword and can be called without creating an object.

3

Add the main method to call static methods

Add a public static void main(String[] args) method inside the Calculator class. Inside it, call Calculator.add(5, 7) and store the result in an int variable named sum. Also call Calculator.multiply(5, 7) and store the result in an int variable named product.

Java

public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static int multiply(int a, int b) {
        return a * b;
    }

    // Add main method below
    // Your code here
}

Hint

The main method is the program's entry point. Use the class name to call static methods.

4

Print the results

Inside the main method, add two System.out.println statements to print the values of sum and product. The first line should print exactly Sum: 12 and the second line should print exactly Product: 35.

Java

public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static int multiply(int a, int b) {
        return a * b;
    }

    public static void main(String[] args) {
        int sum = Calculator.add(5, 7);
        int product = Calculator.multiply(5, 7);
        // Print sum and product below
        // Your code here
    }
}

Hint

Use System.out.println to print text and variables. Use + to join strings and variables.

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