Snakes — Concurrent & Distributed Multiplayer Snake Game

A multiplayer Snake game built in Java that demonstrates concurrent and distributed programming concepts. Features AI-controlled snakes, moving obstacles, a local GUI, and a client-server architecture for remote play.

Developed for the Concurrent and Distributed Programming (PCD) course at ISCTE.

Gameplay

• Automatic snakes navigate a 30x30 grid, pathfinding towards a shared goal
• Human players connect remotely via a client and control a snake with arrow keys
• Obstacles move independently across the board (up to 3 moving simultaneously)
• Goals spawn at random positions; capturing one grows the snake and increments the goal's value (max 10)
• Snakes compete for the same goal — the game ends when a completion condition is met

Architecture

The project is split into four packages reflecting its concurrent and distributed design:

src/
├── gui/ # Presentation layer
│ ├── Main.java # Entry point — creates LocalBoard, GUI, and Server
│ ├── SnakeGui.java # Swing GUI (800x800), Observer pattern for board updates
│ └── BoardComponent.java # Custom JComponent for rendering the grid
│
├── environment/ # Shared game state
│ ├── Board.java # Abstract — 30x30 cell grid, snake/obstacle/goal management
│ ├── LocalBoard.java # Concrete board with thread pool for obstacle movers
│ ├── Cell.java # Thread-safe cell with ReentrantLock + Condition
│ ├── BoardPosition.java # Grid coordinate
│ └── GameState.java # Serializable snapshot (cells, snakes, finished flag)
│
├── game/ # Game entities (each runs in its own thread)
│ ├── Snake.java # Abstract — Thread subclass, movement, growth, initial positioning
│ │ ├── AutomaticSnake.java # AI pathfinding towards goal, random fallback when trapped
│ │ └── HumanSnake.java # Remote-controlled via ReentrantLock + Condition (producer-consumer)
│ ├── Goal.java # Capturable target with incrementing value
│ ├── Obstacle.java # Movable barrier (3 moves each, 2s interval)
│ ├── ObstacleMover.java # Thread that drives obstacle movement
│ ├── GameElement.java # Base class for all board elements
│ └── Server.java # Socket server for remote clients
│
└── remote/ # Client-side networking
├── Client.java # Connects to server, receives GameState via ObjectInputStream
├── RemoteBoard.java # Board subclass — renders server state, sends key input
└── Direction.java # Enum: UP, DOWN, LEFT, RIGHT

Concurrency Model

Concept	Implementation
Snake threads	Each Snake extends Thread and runs its own movement loop
Obstacle thread pool	LocalBoard uses an ExecutorService with 3 simultaneous ObstacleMover threads
Cell locking	Cell uses ReentrantLock + Condition — snakes block on request() until a cell is free
Deadlock prevention	Cell.goalCaptureAndMoveHandler() acquires locks in position order to prevent circular waits
Human input sync	HumanSnake uses a ReentrantLock + Condition (producer-consumer) to bridge network input and game loop
Game state broadcast	Server runs a dedicated thread that periodically serializes GameState to all connected clients
Observer pattern	Board extends Observable; SnakeGui observes and repaints on every state change

Client-Server Model

┌─────────────┐ TCP :12345 ┌─────────────────┐
│ Client │ ◄──── GameState (obj) ──── │ Server │
│ RemoteBoard │ ───── Direction (text) ──► │ ConnectionHandler│
│ SnakeGui │ │ LocalBoard │
└─────────────┘ └─────────────────┘

• Server (Main.java): Creates a LocalBoard, launches the GUI, starts accepting client connections
• Client (Client.java): Connects to the server, receives serialized GameState objects, renders them on a RemoteBoard
• Input: Arrow key presses are converted to Direction enums and sent as text over the socket
• State sync: The server broadcasts the full board state at regular intervals (REMOTE_CONNECTION_SETUP_DELAY)

Controls

Key	Action
Arrow keys	Move the human-controlled snake (remote client only)
Reset button	Interrupt and re-randomize automatic snake directions (local GUI only)

Configuration

Key constants defined across the codebase:

Constant	Value	Location
Grid size	30 x 30	Board.java
Snakes	2	LocalBoard.java
Obstacles	25	LocalBoard.java
Simultaneous movers	3	LocalBoard.java
Obstacle moves	3 per obstacle	Obstacle.java
Obstacle interval	2000 ms	Obstacle.java
Player move interval	200 ms	Board.java
Server port	12345	Server.java
Max goal value	10	Goal.java

Prerequisites

• Java 8+
• IntelliJ IDEA or Eclipse (project files included for both)

Running

Local Mode (with server)

Run gui.Main — starts the local board, GUI, and server:

javac -d out src/**/*.java
java -cp out gui.Main

Remote Client Run remote.Client to connect to a running server:

java -cp out remote.Client

Connects to localhost:12345 by default.

Authors

• Joao Marques
• Tiago