Method overloading in Java - Mini Project: Build & Apply

Method overloading

📖 Scenario: You are creating a simple calculator program that can add numbers. Sometimes you want to add two numbers, and other times you want to add three numbers.

🎯 Goal: Build a Java program that uses method overloading to add two or three numbers using the same method name add.

📋 What You'll Learn

Create a class called Calculator

Create two add methods in the Calculator class: one that adds two integers, and one that adds three integers

Create a main method to test both add methods

Print the results of adding two numbers and three numbers

💡 Why This Matters

🌍 Real World

Method overloading is used in many programs to perform similar actions with different inputs, like calculators, printers, or data processors.

💼 Career

Understanding method overloading is important for writing clean, reusable code and is a common skill asked in programming interviews.

1

Create the Calculator class with the main method

Create a public class called Calculator and add a public static void main(String[] args) method inside it.

Java

public class Calculator {
    public static void main(String[] args) {
        // Your code here
    }
}

Hint

Start by writing the class and main method exactly as shown.

2

Add the first add method for two integers

Inside the Calculator class but outside the main method, create a public static method called add that takes two int parameters named a and b and returns their sum as an int.

Java

public class Calculator {
    public static void main(String[] args) {
        
    }

    // Your code here
}

Hint

Write a method named add that returns the sum of two integers.

3

Add the second add method for three integers

Inside the Calculator class but outside the main method, create another public static method called add that takes three int parameters named a, b, and c and returns their sum as an int.

Java

public class Calculator {
    public static void main(String[] args) {
        
    }

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

    // Your code here
}

Hint

Create another add method with three parameters to add three numbers.

4

Call both add methods and print the results

Inside the main method, call add(5, 10) and store the result in an int variable named sumTwo. Then call add(3, 7, 2) and store the result in an int variable named sumThree. Finally, print both sumTwo and sumThree using System.out.println.

Java

public class Calculator {
    public static void main(String[] args) {
        // Your code here
    }

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

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

Hint

Call both add methods with the given numbers and print the results.

Practice

1.

What is method overloading in Java?

easy

A. Changing the return type of a method only

B. Having multiple classes with the same name

C. Using inheritance to override methods

D. Having multiple methods with the same name but different parameters

Solution

1. Step 1: Understand method naming

   Method overloading means methods share the same name.

2. Step 2: Check parameter differences

   They differ by number or type of parameters, not just return type.

3. Final Answer:

   Having multiple methods with the same name but different parameters -> Option D

4. Quick Check:

   Same name + different parameters = method overloading [OK]

Hint: Same method name, different parameters means overloading [OK]

Common Mistakes:

• Confusing overloading with overriding
• Thinking return type alone overloads method
• Mixing class names with method names

2.

Which of the following is a correct method overloading example in Java?

class Test {
  void show(int a) {}
  void show(int a, int b) {}
  void show(int a) {}
}

easy

A. This code compiles without errors

B. Duplicate method show(int a) causes a compile error

C. Method names must be different to overload

D. Return types must differ for overloading

Solution

1. Step 1: Check method signatures

   Two methods have the same name and same parameter list: show(int a).

2. Step 2: Understand overloading rules

   Overloading requires different parameter lists; duplicate signatures cause errors.

3. Final Answer:

   Duplicate method show(int a) causes a compile error -> Option B

4. Quick Check:

   Same parameters = error, not overloading [OK]

Hint: Parameters must differ; identical signatures cause errors [OK]

Common Mistakes:

• Assuming return type difference overloads method
• Ignoring duplicate parameter lists
• Thinking method names must differ

3.

What is the output of this Java code?

class Demo {
  void print(int a) {
    System.out.println("int: " + a);
  }
  void print(String s) {
    System.out.println("String: " + s);
  }
}
public class Main {
  public static void main(String[] args) {
    Demo d = new Demo();
    d.print(5);
    d.print("hello");
  }
}

medium

A. int: 5\nString: hello

B. String: 5\nint: hello

C. int: 5\nint: hello

D. Compilation error

Solution

1. Step 1: Identify method calls and parameters

   First call passes int 5, second call passes String "hello".

2. Step 2: Match calls to overloaded methods

   print(int) prints "int: 5", print(String) prints "String: hello".

3. Final Answer:

   int: 5 String: hello -> Option A

4. Quick Check:

   Correct method chosen by parameter type [OK]

Hint: Method chosen by argument type matches parameter [OK]

Common Mistakes:

• Mixing output order
• Assuming wrong method called
• Expecting compile error

4.

Find the error in this code snippet:

class Calculator {
  int add(int a, int b) { return a + b; }
  double add(double a, double b) { return a + b; }
  int add(int a, int b, int c) { return a + b + c; }
  int add(int a, int b) { return a - b; }
}

medium

A. Duplicate method add(int a, int b) with different body causes error

B. Overloading requires different method names

C. Return type difference causes error

D. No error, code compiles fine

Solution

1. Step 1: Check method signatures

   Two methods have signature add(int a, int b) but different bodies.

2. Step 2: Understand overloading rules

   Overloading requires unique parameter lists; duplicate signatures cause errors regardless of body.

3. Final Answer:

   Duplicate method add(int a, int b) with different body causes error -> Option A

4. Quick Check:

   Same parameters = duplicate method error [OK]

Hint: Same parameters, different body = error, not overloading [OK]

Common Mistakes:

• Thinking different return types fix duplicates
• Ignoring duplicate parameter lists
• Confusing overloading with overriding

5.

Consider this class:

class Converter {
  int convert(String s) { return Integer.parseInt(s); }
  int convert(int i) { return i * 2; }
  int convert(String s, int base) { return Integer.parseInt(s, base); }
}
public class Main {
  public static void main(String[] args) {
    Converter c = new Converter();
    System.out.println(c.convert("10"));
    System.out.println(c.convert(10));
    System.out.println(c.convert("10", 16));
  }
}

What is the output when this code runs?

hard

A. Runtime error parsing string

B. 10\n20\n10

C. 10\n20\n16

D. Compilation error due to ambiguous methods

Solution

1. Step 1: Analyze each method call

   convert("10") parses string "10" as decimal 10; convert(10) doubles 10 to 20; convert("10", 16) parses hex "10" as decimal 16.

2. Step 2: Determine output values

   Outputs are 10, 20, and 16 respectively.

3. Final Answer:

   10 20 16 -> Option C

4. Quick Check:

   Overloaded methods handle inputs correctly [OK]

Hint: Match method by parameters; parseInt with base converts hex [OK]

Common Mistakes:

• Confusing hex parsing result
• Expecting compile or runtime errors
• Mixing method outputs