Method Fundamentals

What Is a Method

A method represents the smallest executable unit within a program.

When to Use Methods

Extract repetitive code and logically independent functionality into methods.

Benefits of Methods

• Improves code reusability
• Enhances code maintainability

Method Syntax

public static returnType methodName(parameterList) {
    // method body
    return value;
}

Method Invocation

Direct Call

methodName(arguments);

Assignment Call

dataType variable = methodName(arguments);

Output Call

System.out.println(methodName(arguments));

Arguments vs Parameters

Actual arguments refer to the values passed during method invocation.

Formal parameters refer to the variables defined in the method signature.

When invoking a method, actual arguments and formal parameters must match in order and type, otherwise compilation errors occur.

Method Design Strategy

What does this method need to accomplish? → method body
What inputs are required to complete the task? → parameters

Method Overloading

Method overloading occurs when multiple methods with the same name exist within a single class. These methods perform similar functionality but differ in parameter types or parameter counts.

Key point: Within the same class, methods with identical names but different parameters constitute an overload relationship. Return types are irrelevant.

Parameter differences include:

• Different parameter counts
• Different parameter types
• Different parameter order

Practice Exercises

Array Copying

import java.util.Arrays;

public class ArrayCopyDemo {
    public static void main(String[] args) {
        int[] source = {10, 20, 30, 40, 50, 60, 70};
        
        int[] result = extractPortion(source, 2, 6);
        
        System.out.println("Copied array: " + Arrays.toString(result));
    }
    
    public static int[] extractPortion(int[] data, int startIndex, int endIndex) {
        int[] destination = new int[endIndex - startIndex];
        
        int position = 0;
        for (int i = startIndex; i < endIndex; i++) {
            destination[position] = data[i];
            position++;
        }
        return destination;
    }
}

IDEA Tip: Press Ctrl+Alt+M to quick extract code into a new method.

Prime Number Detection

public class PrimeDetector {
    public static void main(String[] args) {
        int primeCount = 0;
        
        for (int candidate = 101; candidate <= 200; candidate++) {
            boolean isPrime = true;
            
            for (int divisor = 2; divisor < candidate; divisor++) {
                if (candidate % divisor == 0) {
                    isPrime = false;
                    break;
                }
            }
            
            if (isPrime) {
                System.out.println(candidate + " is prime");
                primeCount++;
            }
        }
        
        System.out.println("Total primes found: " + primeCount);
    }
}

Captcha Generation

import java.util.Random;

public class CaptchaGenerator {
    public static void main(String[] args) {
        char[] letters = new char[52];
        
        for (int i = 0; i < letters.length; i++) {
            if (i < 26) {
                letters[i] = (char) ('a' + i);
            } else {
                letters[i] = (char) ('A' + i - 26);
            }
        }
        
        System.out.println("Available characters: ");
        for (char c : letters) {
            System.out.print(c + " ");
        }
        System.out.println();
        
        Random generator = new Random();
        StringBuilder captcha = new StringBuilder();
        
        for (int i = 0; i < 4; i++) {
            int index = generator.nextInt(letters.length);
            char chosen = letters[index];
            captcha.append(chosen);
        }
        
        int digit = generator.nextInt(10);
        captcha.append(digit);
        
        System.out.println("Generated captcha: " + captcha.toString());
    }
}