Method declaration in Java - Mini Project: Build & Apply

Method declaration

📖 Scenario: You are creating a simple Java program to greet users by name. This program will help you understand how to declare and use methods in Java.

🎯 Goal: Build a Java program that declares a method called greetUser which takes a String parameter called name and prints a greeting message including that name.

📋 What You'll Learn

Declare a method named greetUser that takes one String parameter called name

The method should print the message: Hello, <name>! where <name> is the parameter value

Call the greetUser method from the main method with the argument "Alice"

Print the greeting message to the console

💡 Why This Matters

🌍 Real World

Methods are used in all Java programs to organize code into small, reusable pieces that perform specific tasks.

💼 Career

Understanding method declaration is essential for any Java developer, as it is the foundation for writing clean, maintainable, and reusable code.

1

Create the main class and main method

Create a public class named Greeting and inside it, write the main method with the exact signature public static void main(String[] args).

Java

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

Hint

The main method is the entry point of a Java program. Use the exact signature public static void main(String[] args).

2

Declare the greetUser method

Inside the Greeting class but outside the main method, declare a public static method named greetUser that takes a String parameter called name and returns nothing (void).

Java

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

    // Your code here
}

Hint

Method declaration syntax: public static void greetUser(String name) means the method is public, static, returns nothing, and takes one String parameter.

3

Add print statement inside greetUser method

Inside the greetUser method, write a System.out.println statement that prints the message Hello, <name>! using the parameter name with string concatenation.

Java

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

    public static void greetUser(String name) {
        // Your code here
    }
}

Hint

Use System.out.println("Hello, " + name + "!") to print the greeting message.

4

Call greetUser method from main

Inside the main method, call the greetUser method with the argument "Alice" to display the greeting message.

Java

public class Greeting {
    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 writing greetUser("Alice"); inside the main method.

Practice

1. What is the correct way to declare a method in Java that returns an integer and takes no parameters?

easy

A. int getNumber { return 5; }

B. public int getNumber() { return 5; }

C. public getNumber() int { return 5; }

D. public int getNumber[] { return 5; }

Solution

1. Step 1: Check method signature format

   The correct method declaration includes access modifier, return type, method name, and parentheses for parameters.

2. Step 2: Validate syntax correctness

   public int getNumber() { return 5; } correctly uses 'public int getNumber()' with parentheses and a return statement.

3. Final Answer:

   public int getNumber() { return 5; } -> Option B

4. Quick Check:

   Method declaration = public int getNumber() { ... } [OK]

Hint: Method declaration needs return type, name, and parentheses [OK]

Common Mistakes:

• Omitting parentheses after method name
• Missing return type before method name
• Using brackets [] instead of parentheses for parameters

2. Which of the following is a correct method declaration syntax in Java?

easy

A. void printMessage(String message) { System.out.println(message); }

B. void printMessage(String message); { System.out.println(message); }

C. void printMessage String message { System.out.println(message); }

D. void printMessage(String message) System.out.println(message);

Solution

1. Step 1: Identify correct method header and body syntax

   Method header must have parentheses around parameters and body enclosed in braces.

2. Step 2: Check for syntax errors

   void printMessage(String message) { System.out.println(message); } correctly declares method with parameters in parentheses and body in braces.

3. Final Answer:

   void printMessage(String message) { System.out.println(message); } -> Option A

4. Quick Check:

   Method syntax = returnType name(params) { body } [OK]

Hint: Method parameters must be inside parentheses and body inside braces [OK]

Common Mistakes:

• Adding semicolon after method header
• Missing parentheses around parameters
• Omitting braces for method body

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

public class Test {
  public static int add(int a, int b) {
    return a + b;
  }
  public static void main(String[] args) {
    System.out.println(add(3, 4));
  }
}

medium

A. 0

B. 34

C. 7

D. Error

Solution

1. Step 1: Understand method call and parameters

   The method add takes two integers and returns their sum.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 3 + 4 = 7, which is printed.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Method add returns sum; 3 + 4 = 7 [OK]

Common Mistakes:

• Confusing concatenation with addition
• Expecting compile error due to static method
• Ignoring return value and expecting no output

4. Identify the error in the following method declaration:

public int multiply(int x, int y)
  return x * y;
}

medium

A. Extra semicolon after return statement

B. Missing return type

C. Incorrect parameter types

D. Missing opening brace '{' after method header

Solution

1. Step 1: Check method header and body braces

   The method header must be followed by an opening brace '{' to start the method body.

2. Step 2: Identify missing brace

   The code lacks '{' after the method header, causing a syntax error.

3. Final Answer:

   Missing opening brace '{' after method header -> Option D

4. Quick Check:

   Method body must start with '{' [OK]

Hint: Method body always starts with '{' after header [OK]

Common Mistakes:

• Forgetting opening brace '{'
• Placing return statement outside method body
• Confusing semicolon placement

5. You want to declare a method named filterPositive that takes an array of integers and returns a new array containing only the positive numbers. Which method declaration is correct?

hard

A. public int[] filterPositive(int[] numbers) { /* implementation */ }

B. public int filterPositive(int numbers[]) { /* implementation */ }

C. public void filterPositive(int[] numbers) { /* implementation */ }

D. public int filterPositive(int[] numbers[]) { /* implementation */ }

Solution

1. Step 1: Determine return type and parameter type

   The method returns an array of integers, so return type must be int[]. The parameter is an int array.

2. Step 2: Check syntax correctness

   public int[] filterPositive(int[] numbers) { /* implementation */ } correctly declares return type as int[] and parameter as int[]. Other options have wrong return types or parameter syntax.

3. Final Answer:

   public int[] filterPositive(int[] numbers) { /* implementation */ } -> Option A

4. Quick Check:

   Return type matches output array type [OK]

Hint: Return type must match method output type (int[] for array) [OK]

Common Mistakes:

• Using int instead of int[] as return type
• Incorrect parameter array syntax
• Using void when method returns data