Methods in Java

public class MethodStructure {
    // Method signature: return_type methodName(parameters)
    
    // Simple method with no parameters and no return value
    public static void sayHello() {
        System.out.println("Hello, World!");
    }
    
    // Method with parameters
    public static void greet(String name) {
        System.out.println("Hello, " + name + "!");
    }
    
    // Method with parameters and return value
    public static int add(int a, int b) {
        return a + b;
    }
    
    // Method with multiple parameters of different types
    public static void printPersonInfo(String name, int age, boolean isStudent) {
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Student: " + isStudent);
    }
    
    public static void main(String[] args) {
        // Calling methods
        sayHello();
        greet("John");
        
        int sum = add(5, 3);
        System.out.println("Sum: " + sum);
        
        printPersonInfo("Alice", 25, true);
    }
}

public class MethodOverloading {
    // Method with int parameter
    public static void display(int number) {
        System.out.println("Integer: " + number);
    }
    
    // Method with double parameter
    public static void display(double number) {
        System.out.println("Double: " + number);
    }
    
    // Method with String parameter
    public static void display(String text) {
        System.out.println("String: " + text);
    }
    
    // Method with multiple parameters
    public static void display(String text, int number) {
        System.out.println(text + ": " + number);
    }
    
    public static void main(String[] args) {
        display(100);
        display(99.99);
        display("Hello");
        display("Age", 25);
    }
}

public class VarargsExample {
    // Method with variable arguments
    public static int sum(int... numbers) {
        int total = 0;
        for (int num : numbers) {
            total += num;
        }
        return total;
    }
    
    // Method with fixed parameters plus varargs
    public static void printDetails(String name, int... scores) {
        System.out.println("Student: " + name);
        System.out.println("Scores: ");
        for (int score : scores) {
            System.out.println("  " + score);
        }
    }
    
    public static void main(String[] args) {
        // Can call with any number of arguments
        System.out.println("Sum of 2 numbers: " + sum(10, 20));
        System.out.println("Sum of 4 numbers: " + sum(10, 20, 30, 40));
        System.out.println("Sum of 1 number: " + sum(100));
        
        printDetails("John", 85, 92, 78);
    }
}

public class RecursiveExample {
    // Factorial calculation using recursion
    public static int factorial(int n) {
        if (n <= 1) {
            return 1;
        }
        return n * factorial(n - 1);
    }
    
    // Fibonacci sequence
    public static int fibonacci(int n) {
        if (n <= 1) {
            return n;
        }
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
    
    public static void main(String[] args) {
        System.out.println("Factorial of 5: " + factorial(5));
        System.out.println("Factorial of 7: " + factorial(7));
        
        System.out.println("Fibonacci of 6: " + fibonacci(6));
        System.out.println("Fibonacci of 8: " + fibonacci(8));
    }
}

public class StaticVsInstance {
    // Static method (belongs to class)
    public static void staticMethod() {
        System.out.println("This is a static method");
    }
    
    // Instance method (belongs to object)
    public void instanceMethod() {
        System.out.println("This is an instance method");
    }
    
    public static void main(String[] args) {
        // Call static method directly
        staticMethod();
        
        // Create object to call instance method
        StaticVsInstance obj = new StaticVsInstance();
        obj.instanceMethod();
    }
}