Design and Implementation of a Simple Plants vs Zombies Game in Java

This article describes the creation of a simplified Plants vs Zombies clone using Java, extracting the mini‑level with a rolling machine that randomly generates plant cards and zombies, and explaining the overall game flow and visual layout.

Game objects are modeled with an abstract class Zombie that defines common attributes (width, height, live, x, y) and state constants (LIFE, ATTACK, DEAD). Similar abstract classes exist for plants and bullets, while shared behaviors such as shooting are extracted into an interface Shoot with a method Bullet[] shoot() .

Pause functionality is implemented by adding a mouse listener: when the mouse moves outside the game window, the mouseMoved(MouseEvent e) method sets the game status to pause . A keyboard listener could provide a more user‑friendly alternative.

Objects are managed with Java collections. Zombies are stored in a List<Zombie> zombies and generated randomly by the public Zombie nextOneZombie() method, which selects one of four zombie subclasses based on a random number. Entrance timing is controlled by an integer counter ( zombieEnterTime ) and modulo logic to add new zombies at regular intervals.

Plant placement uses two lists: List<Plant> plants for cards on the rolling machine and List<Plant> plantsLife for plants already on the lawn. The plantBangAction() method iterates over the rolling‑machine list, updates states (stop, wait) based on Y‑coordinate checks, and moves plants to the lawn when appropriate.

Complex boolean conditions for collision detection were refactored for readability. The original combined condition was split into separate if statements that break early, improving maintainability and reducing nesting.

Movement actions are defined for bullets and zombies. public void BulletStepAction() iterates over a bullets list and calls b.step() for each bullet. public void zombieStepAction() uses a step counter ( zombieStepTime ) and moves only living zombies at a fixed interval.

Attack logic is encapsulated in public boolean zombieHit(Plant p) , which computes the overlapping rectangle between a zombie and a plant. The zombieHitAction() method iterates over all zombies and plants on the lawn, changes zombie state to ATTACK when a collision is detected, and reduces plant health via p.loseLive() . A bug note mentions that selected plants should be excluded from attack checks.

A reward system is introduced with an interface Award that defines constants CLEAR and STOP and an abstract method int getAwardType() . In checkZombieAction() , dead zombies that implement Award trigger either a full‑screen clear or a pause effect based on the award type.

Background music is added by creating a Runnable implementation ( class zombieAubio implements Runnable ) that loads and plays a WAV file on a separate thread, demonstrating how to integrate audio playback into the game loop.

The article concludes with suggested future improvements: expanding plant varieties, adding special zombies with unique behaviors (e.g., pole‑vaulting zombies), refining plant attack cessation when no zombies are in range, and improving configuration management for easier parameter tuning.