Java Functions Tutorial

Functions in Java, often referred to as methods, are blocks of code that perform a specific task. They help in organizing code, improving reusability, and making programs easier to read and maintain. This tutorial will guide you through the basics of defining, calling, and using functions in Java, including parameter passing, return values, and function overloading.

By the end of this tutorial, you'll understand how to create and use functions effectively in Java, enabling you to write modular and efficient code.

What is a Function?

A function is a reusable block of code that performs a specific task. It has a name, a return type, and optionally, a list of parameters.

Function Signature: The combination of the function name and its parameter list.
Return Type: The data type of the value the function returns. Use void if the function does not return a value.
Parameters: Variables passed to the function for processing.

// Function definition
public int add(int a, int b) {
    return a + b;
}

Defining and Calling Functions

Defining a Function:

Syntax:

returnType functionName(parameterList) {
    // Function body
}

Example:

public void greet() {
    System.out.println("Hello, World!");
}

Calling a Function:
- Use the function name followed by parentheses.
- Example:
```
greet(); // Calls the greet function
```

Function Parameters and Return Values

Parameters:
- Functions can accept input values through parameters.
- Example:
```
public void printMessage(String message) {
    System.out.println(message);
}
```
Return Values:
- Functions can return a value using the return keyword.
- Example:
```
public int multiply(int a, int b) {
    return a * b;
}
```

Function Overloading

Function overloading allows you to define multiple functions with the same name but different parameter lists.

Rules for Overloading:
- Functions must have the same name but different parameter lists (different number or types of parameters).
- Return type alone is not sufficient to differentiate overloaded functions.

Example:

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

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

Example: Using Functions

public class Main {
    // Function to add two integers
    public static int add(int a, int b) {
        return a + b;
    }

    // Function to print a message
    public static void printMessage(String message) {
        System.out.println(message);
    }

    // Function to calculate factorial
    public static int factorial(int n) {
        if (n == 0) {
            return 1;
        }
        return n * factorial(n - 1);
    }

    public static void main(String[] args) {
        // Calling functions
        int sum = add(5, 3);
        printMessage("Sum: " + sum);

        int fact = factorial(5);
        printMessage("Factorial of 5: " + fact);
    }
}

This example demonstrates how to define and use functions in Java. You can modify and experiment with the code to deepen your understanding.

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