Methods and Functions Lesson

Building Reusable Code Blocks

Methods, or functions, are the building blocks of organized code. They allow you to bundle a specific task into a reusable, named block, making your programs more modular, readable, and easier to debug.

Why Use Methods?

As programs grow, you'll find yourself performing the same tasks repeatedly. Instead of copying and pasting code, you can define a method. This approach is essential for writing professional-quality code.

The Core Benefits

Modularity: Break down complex problems into smaller, manageable pieces.
Reusability: Write code once and call it from anywhere, as many times as you need.
Readability: Give a descriptive name to a block of code, making its purpose clear.
Maintainability: If you need to fix a bug or make a change, you only need to update the code in one place: the method itself.

The Anatomy of a Method

Every method in Java has a "signature" that defines its properties. This signature tells the compiler what the method is called, what kind of data it needs, and what kind of data it will return.

public static int calculateScore(int currentScore, int pointsToAdd) {
    int newScore = currentScore + pointsToAdd;
    return newScore;
}

Breaking Down the Signature: `public static int calculateScore(...)`

`public`: The access modifier. `public` means this method can be called from anywhere in your code.
`static`: A keyword meaning the method belongs to the class itself, not a specific object. For now, most of our methods will be `static`.
`int`: The return type. This method must return a value of type `int`. If a method returns nothing, this is set to `void`.
`calculateScore`: The method name. By convention, method names in Java use `camelCase`.
`(int currentScore, int pointsToAdd)`: The parameter list. These are the input values the method needs to do its job.

Parameters vs. Arguments

These terms are often used interchangeably, but they have distinct meanings:

Parameters: The variables listed in the method's definition (e.g., `currentScore`, `pointsToAdd`). They are placeholders for the data.
Arguments: The actual values you provide when you call the method (e.g., `100`, `50`).

Returning Values

A method can perform a calculation and send a result back to the code that called it. This is called a "return value." The `return` keyword is used to send this value back and immediately exit the method.

If a method is not meant to return any value, its return type is declared as `void`.

// A method that returns a value
public static double getAverage(double a, double b) {
    return (a + b) / 2.0;
}

// A method that performs an action but returns nothing (void)
public static void printWarning(String message) {
    System.out.println("WARNING: " + message);
}

// Calling the methods
double avg = getAverage(10.0, 20.0); // avg is now 15.0
printWarning("Sensor offline!");      // Prints a message to the console

Test Your Knowledge

Question: Given the method signature `public boolean isMotorAtLimit()`, what type of value does this method return?