Method parameters in Java - Mini Project: Build & Apply

Method parameters

📖 Scenario: You are creating a simple calculator program that can add two numbers. You will learn how to use method parameters to pass values into a method.

🎯 Goal: Build a Java program with a method called add that takes two numbers as parameters and returns their sum. Then, call this method and print the result.

📋 What You'll Learn

Create a method named add with two int parameters named a and b

The add method should return the sum of a and b

Call the add method with the numbers 5 and 7

Print the result of the add method call

💡 Why This Matters

🌍 Real World

Methods with parameters are used everywhere in programming to perform tasks with different inputs, like calculators, games, and apps.

💼 Career

Understanding method parameters is essential for writing reusable and organized code, a key skill for any software developer.

1

Create the main class and main method

Create a public class named Calculator and add the main method inside it.

Java

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

Hint

Start by typing public class Calculator { and then add the main method inside.

2

Create the add method with parameters

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

Java

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

Hint

Define the method with public static int add(int a, int b) and return the sum using return a + b;.

3

Call the add method in main

Inside the main method, call the add method with the numbers 5 and 7 and store the result in an int variable named result.

Java

public class Calculator {
    public static void main(String[] args) {
        // Your code here
    }
    public static int add(int a, int b) {
        return a + b;
    }
}

Hint

Use int result = add(5, 7); inside the main method to call the add method.

4

Print the result

Add a line inside the main method to print the value of the result variable using System.out.println.

Java

public class Calculator {
    public static void main(String[] args) {
        int result = add(5, 7);
        // Your code here
    }
    public static int add(int a, int b) {
        return a + b;
    }
}

Hint

Print the result using System.out.println(result);.

Practice

1. What is the purpose of method parameters in Java?
public void greet(String name) { ... }

easy

A. To declare variables inside the method

B. To define the method's return type

C. To send data into methods so they can use it inside

D. To specify the method's access level

Solution

1. Step 1: Understand method parameters

   Method parameters are variables listed in the method definition that accept values when the method is called.

2. Step 2: Identify their purpose

   They allow sending data into the method so it can perform actions using that data.

3. Final Answer:

   To send data into methods so they can use it inside -> Option C

4. Quick Check:

   Parameters pass data into methods [OK]

Hint: Parameters pass info into methods for flexible use [OK]

Common Mistakes:

• Confusing parameters with return types
• Thinking parameters declare variables inside method body
• Mixing parameters with access modifiers

2. Which of the following is the correct syntax to declare a method with two parameters in Java?

easy

A. public void add(int a; int b) { }

B. public void add(int a, int b) { }

C. public void add(int a int b) { }

D. public void add(int a & int b) { }

Solution

1. Step 1: Recall parameter syntax

   Parameters are listed inside parentheses separated by commas, each with a type and name.

2. Step 2: Check each option

   public void add(int a, int b) { } uses commas correctly; others use semicolon, missing comma, or invalid symbol.

3. Final Answer:

   public void add(int a, int b) { } -> Option B

4. Quick Check:

   Parameters separated by commas [OK]

Hint: Parameters must be comma-separated with type and name [OK]

Common Mistakes:

• Using semicolons instead of commas
• Omitting commas between parameters
• Using invalid symbols like &

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

public class Test {
  public static void printSum(int x, int y) {
    System.out.println(x + y);
  }
  public static void main(String[] args) {
    printSum(5, 3);
  }
}

medium

A. 8

B. 53

C. x + y

D. Compile error

Solution

1. Step 1: Understand method call with parameters

   The method printSum is called with 5 and 3 as arguments, assigned to x and y.

2. Step 2: Calculate the sum inside the method

   Inside printSum, it prints x + y which is 5 + 3 = 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Sum parameters values to get output [OK]

Common Mistakes:

• Concatenating numbers as strings
• Expecting variable names printed
• Thinking code won't compile

4. Identify the error in this method declaration:

public void displayMessage(String message, int) {
  System.out.println(message);
}

medium

A. Parameter list missing variable name for int type

B. Method must return a value

C. Cannot use String as parameter type

D. System.out.println is invalid here

Solution

1. Step 1: Check parameter list syntax

   Each parameter must have a type and a variable name. Here, int has no name.

2. Step 2: Identify the error

   Missing variable name after int causes a syntax error.

3. Final Answer:

   Parameter list missing variable name for int type -> Option A

4. Quick Check:

   Parameters need type and name [OK]

Hint: Every parameter needs a name after its type [OK]

Common Mistakes:

• Omitting parameter names
• Thinking return type is missing
• Misunderstanding print statement usage

5. You want to create a method that calculates the area of a rectangle. Which method signature correctly uses parameters to accept the rectangle's width and height as doubles?

hard

A. public void area(double width; double height)

B. public double area(width, height)

C. public double area(int width, int height)

D. public double area(double width, double height)

Solution

1. Step 1: Identify correct parameter types and syntax

   The method should accept two double parameters named width and height, separated by commas.

2. Step 2: Evaluate each option

   public double area(double width, double height) correctly declares two double parameters with names and commas; public double area(width, height) misses types; public double area(int width, int height) uses int instead of double; public void area(double width; double height) uses semicolon instead of comma and void return type.

3. Final Answer:

   public double area(double width, double height) -> Option D

4. Quick Check:

   Parameters need type, name, comma-separated [OK]

Hint: Use type and name with commas for parameters [OK]

Common Mistakes:

• Omitting parameter types
• Using wrong separators like semicolons
• Using wrong data types for precision