Design Patterns

Composite

In World class addObject(Actor object, int x, int y)
Each class extending Actor implements its own act method

Observer

1. In class LevelCounter: Keep watching the changes in level, and update it

public void act() {
    if (Space.level != level) {
        level = Space.level;
        updateImage();
    }
}

2. In Class Counter:

public void act() {
    updateImage();
    ...
}

#### Workflow
Bullet:
private void checkAsteroidHit() {
  ...
  asteroid.hit(damage);
}

Asteroid:
public void hit(int damage) {
    Counter.add(damage * Space.level);
    ...
}

Counter:
public static void add(int score) {
    value += score;
}

private void updateImage() {
    ...
    image.drawString(text + ...);
}

Chain of Responsibility

1. In class Bullet:

private void checkAsteroidHit() {
    Asteroid asteroid = (Asteroid) getOneIntersectingObject(Asteroid.class);
    ...
}

// Behind the scene
Traverse through the array of asteroids and check
if one of them is intersected by asking every asteroid
if it is closed enough to the object

2. In class ProtonWave:

private void checkCollision() {
    int range = getImage().getWidth() / 2;
    List<Asteroid> asteroids = getObjectsInRange(range, Asteroid.class);

    for (Asteroid a : asteroids) {
        a.hit (DAMAGE);
    }
}

// Behind the scene
Traverse through the array of asteroids and check
if some of them are in the given range. Return the asteroids
in the range for take further action.

State

Rocket will have additional equipment after level 3
Note) to be equipped, must ignit engine first
IRocketState, NormalState, AdvancedState

@Class: NormalState
public void ignite() {
    // check the level here
    if(Space.level >= 3) {
        rocket.setState(rocket.getAdvancedState());
    }
    ...
}

Strategy

Different level of play modes; Easy, Normal, Hard

@Class: Counter
public Counter(String prefix, int playMode) {
    switch(playMode) {
        case 1: strategy = new EasyMode(); break;
        case 2: strategy = new NormalMode(); break;
        case 3: strategy = new HardMode(); break;
    }
    ...
}

public void add(int score) {
    strategy.updateScore(score);
}