1.10 Lesson Homework

Popcorn Hack 1

• Good lines
  • sayCatchphrase(); — static method, can be called directly in main()
  • alex.sayHi(); — instance method called on an object
  • alex.sayCatchphrase(); — works (static called from object, though not recommended)
• Bad lines (cause error)
  • sayHi(); — instance method called from static context without an object

class Bro {
    String name;
    static String catchphrase = "Sup bro?";

    // Constructor
    public Bro(String name) {
        this.name = name;
    }

    // Instance method — requires an object to call it
    public void sayHi() {
        System.out.println("Hey, I'm " + name);
    }

    // Static method — belongs to the class
    public static void sayCatchphrase() {
        System.out.println(catchphrase);
    }

    public static void main(String[] args) {
        // Fixed: Call static method using the class name (best practice)
        Bro.sayCatchphrase();

        // Orignal Error: sayHi() is an instance method, cannot call from static context
        // sayHi();

        // Fix: Create an object to call instance method
        Bro alex = new Bro("Alex");

        // Correct: calling instance method on the object
        alex.sayHi();

        // Works but not recommended: calling static method through object
        alex.sayCatchphrase();

        // Fix: better way to call static method
        Bro.sayCatchphrase();
    }
}
Bro.main(new String[]{});

Sup bro?
Hey, I'm Alex
Sup bro?
Sup bro?

Homework

import java.util.Random;

class Warrior {
    // Instance variables
    String name;
    int power;
    int health;

    // Static variable
    static double fightDuration = 0.0; // in seconds

    // Constructor
    public Warrior(String name, int power, int health) {
        this.name = name;
        this.power = power;
        this.health = health;
    }

    // Instance method: attack another warrior
    public void attack(Warrior opponent) {
        System.out.println(this.name + " attacks " + opponent.name + " for " + this.power + " damage!");
        opponent.health -= this.power;

        // Increase fight duration
        fightDuration += 0.5; // half a second per attack
    }

    // Instance method: print warrior status
    public void printStatus() {
        System.out.println(name + " | Health: " + health + " | Power: " + power);
    }

    // Class method: compare which fighter is stronger
    public static Warrior strongerFighter(Warrior w1, Warrior w2) {
        return (w1.power > w2.power) ? w1 : w2;
    }

    // Class method: begin the battle
    public static void beginBattle(Warrior w1, Warrior w2) {
        System.out.println("The battle begins between " + w1.name + " and " + w2.name + "!");
        Random rand = new Random();

        // Battle loop
        while (w1.health > 0 && w2.health > 0) {
            if (rand.nextBoolean()) {
                w1.attack(w2);
            } else {
                w2.attack(w1);
            }
            w1.printStatus();
            w2.printStatus();
            System.out.println("-------------------------");

            try {
                Thread.sleep(500); // delay for readability
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        // Declare winner
        if (w1.health > 0) {
            System.out.println(w1.name + " wins the battle!");
        } else if (w2.health > 0) {
            System.out.println(w2.name + " wins the battle!");
        } else {
            System.out.println("It's a tie!");
        }

        System.out.printf("Fight duration: %.1f seconds%n", fightDuration);
    }
}

public class UltimateBattle {
    public static void main(String[] args) {
        // Create two objects (instance of Warrior)
        Warrior robot = new Warrior("SteelBot", 8, 40);
        Warrior dinosaur = new Warrior("Rexosaurus", 10, 35);

        // Use instance methods
        robot.printStatus();
        dinosaur.printStatus();

        System.out.println("\nStronger fighter is: " + Warrior.strongerFighter(robot, dinosaur).name);

        // Begin battle
        Warrior.beginBattle(robot, dinosaur);
    }
}

UltimateBattle.main(new String[]{});

SteelBot | Health: 40 | Power: 8
Rexosaurus | Health: 35 | Power: 10

Stronger fighter is: Rexosaurus
The battle begins between SteelBot and Rexosaurus!
Rexosaurus attacks SteelBot for 10 damage!
SteelBot | Health: 30 | Power: 8
Rexosaurus | Health: 35 | Power: 10
-------------------------
Rexosaurus attacks SteelBot for 10 damage!
SteelBot | Health: 20 | Power: 8
Rexosaurus | Health: 35 | Power: 10
-------------------------
Rexosaurus attacks SteelBot for 10 damage!
SteelBot | Health: 10 | Power: 8
Rexosaurus | Health: 35 | Power: 10
-------------------------
Rexosaurus attacks SteelBot for 10 damage!
SteelBot | Health: 0 | Power: 8
Rexosaurus | Health: 35 | Power: 10
-------------------------
Rexosaurus wins the battle!
Fight duration: 5.5 seconds