Method calling in Java - Mini Project: Build & Apply

Method calling

📖 Scenario: You are creating a simple Java program to greet users by their names. This program will help you understand how to call methods to reuse code.

🎯 Goal: Build a Java program that defines a method to greet a user by name and calls this method to display a greeting message.

📋 What You'll Learn

Create a method named greetUser that takes a String parameter called name and prints a greeting message.

Call the greetUser method from the main method with a specific name.

Print the greeting message to the console.

💡 Why This Matters

🌍 Real World

Calling methods is how programs reuse code to perform tasks multiple times without repeating code.

💼 Career

Understanding method calling is essential for writing clean, organized, and maintainable Java programs in any software development job.

1

Create the main class and main method

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

Java

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

Hint

The main method is the starting point of any Java program.

2

Create the greetUser method

Inside the GreetingApp class but outside the main method, create a public static method named greetUser that takes a String parameter called name and prints "Hello, " + name + "!".

Java

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

Hint

Define the method outside main but inside the class. Use System.out.println to print.

3

Call the greetUser method from main

Inside the main method, call the greetUser method with the argument "Alice".

Java

public class GreetingApp {
    public static void main(String[] args) {
        // Your code here
    }
    public static void greetUser(String name) {
        System.out.println("Hello, " + name + "!");
    }
}

Hint

Call the method by its name and pass the exact string "Alice" as argument.

4

Print the greeting message

Run the program and print the output to the console. The output should be exactly Hello, Alice!

Java

public class GreetingApp {
    public static void main(String[] args) {
        greetUser("Alice");
        // Your code here
    }
    public static void greetUser(String name) {
        System.out.println("Hello, " + name + "!");
    }
}

Hint

Make sure to run the program and check the console output.

Practice

1. What does calling a method in Java do?
myMethod();

easy

A. Runs the instructions inside the method named myMethod.

B. Creates a new method called myMethod.

C. Deletes the method myMethod from the program.

D. Prints the name myMethod on the screen.

Solution

1. Step 1: Understand what a method call does

   Calling a method means running the code inside that method.

2. Step 2: Analyze the example myMethod();

   This runs the instructions saved inside the method named myMethod.

3. Final Answer:

   Runs the instructions inside the method named myMethod. -> Option A

4. Quick Check:

   Method call = run method code [OK]

Hint: Method call runs code inside method name() [OK]

Common Mistakes:

• Thinking method call creates or deletes methods
• Confusing method call with printing text
• Assuming method call changes method definition

2. Which of the following is the correct way to call a method named displayMessage in Java?

easy

A. run displayMessage();

B. call displayMessage();

C. displayMessage;

D. displayMessage();

Solution

1. Step 1: Recall Java method call syntax

   In Java, you call a method by writing its name followed by parentheses.

2. Step 2: Check each option

   Only displayMessage(); matches the correct syntax for calling a method.

3. Final Answer:

   displayMessage(); -> Option D

4. Quick Check:

   Method call syntax = name() [OK]

Hint: Method call needs parentheses after name [OK]

Common Mistakes:

• Omitting parentheses when calling methods
• Adding extra words like 'call' or 'run'
• Using semicolon without parentheses

3. What is the output of this Java code?

public class Test {
  public static void sayHi() {
    System.out.println("Hi there!");
  }
  public static void main(String[] args) {
    sayHi();
  }
}

medium

A. sayHi()

B. No output

C. Hi there!

D. Compilation error

Solution

1. Step 1: Identify the method call in main

   The main method calls sayHi(), which prints "Hi there!".

2. Step 2: Understand what sayHi() does

   It prints the text "Hi there!" to the screen.

3. Final Answer:

   Hi there! -> Option C

4. Quick Check:

   Method prints text = output text [OK]

Hint: Method prints text, so output is printed string [OK]

Common Mistakes:

• Confusing method name with output
• Expecting no output without print statement
• Thinking method call causes error

4. Find the error in this Java code snippet:

public class Demo {
  public static void greet() {
    System.out.println("Hello!");
  }
  public static void main(String[] args) {
    greet;
  }
}

medium

A. Incorrect method name.

B. Missing parentheses when calling method greet.

C. Missing semicolon after greet.

D. Method greet is not defined.

Solution

1. Step 1: Check method call syntax in main

   The code uses greet; which is missing parentheses.

2. Step 2: Understand correct method call

   Method calls require parentheses even if no arguments: greet();.

3. Final Answer:

   Missing parentheses when calling method greet. -> Option B

4. Quick Check:

   Method call needs () [OK]

Hint: Always use () to call methods, even if empty [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking semicolon alone calls method
• Assuming method call without () is valid

5. Given this Java code:

public class Calculator {
  public static int add(int a, int b) {
    return a + b;
  }
  public static void main(String[] args) {
    int result = add(5, 3);
    System.out.println(result);
  }
}

What will be printed when the program runs?

hard

A. 8

B. 53

C. add(5, 3)

D. Compilation error

Solution

1. Step 1: Understand method add parameters and return

   The method add takes two integers and returns their sum.

2. Step 2: Analyze the call add(5, 3)

   It returns 5 + 3 = 8, which is stored in result.

3. Step 3: Check the output statement

   System.out.println(result); prints the value 8.

4. Final Answer:

   8 -> Option A

5. Quick Check:

   Sum of 5 and 3 = 8 [OK]

Hint: Method returns sum; print shows result [OK]

Common Mistakes:

• Concatenating numbers as strings instead of adding
• Expecting method name printed instead of result
• Confusing return value with method call syntax