Connect 4 Game – Object-Oriented Design Project

Team Members

• Trisha Nookala
• Soumya Devulapalli

Development Environment

• Language: Java
• IDE: IntelliJ IDEA
• Build Tool: Gradle

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🎯 Project Description

This project implements a console-based version of the classic Connect 4 game. The game is played on a 6×7 grid where two players take turns dropping pieces into columns. The goal is to connect four of the same colored pieces in a row (horizontally, vertically, or diagonally).

The system is designed using object-oriented principles and multiple design patterns to ensure modularity, flexibility, and maintainability.

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Design Patterns Used

1. Factory Pattern

Where:

• connect4.factory.PieceFactory
• connect4.factory.PlayerFactory Why All piece and player creation goes through factory classes instead of being scattered across the codebase. This centralizes object creation so that adding a new piece color or player type only requires changing the factory.

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2. Strategy Pattern

Where:

• Win Strategy
• connect4.strategy.WinStrategy (interface)
• connect4.strategy.StandardWinStrategy (implementation)
• connect4.strategy.MoveStrategy (interface)
• Move Strategy
• connect4.strategy.HumanStrategy(implementation)
• connect4.strategy.EasyStrategy(implementation)
• connect4.strategy.MediumStrategy(implementation)
• connect4.strategy.HardStrategy(implementation) Why We used the Strategy pattern in two places. For move selection, each player holds a MoveStrategy — HumanStrategy reads input, EasyStrategy picks randomly, MediumStrategy blocks and wins when possible, and HardStrategy looks ahead using minimax. For win checking, Connect4Game delegates to a WinStrategy. Swapping computer difficulty or win condition only requires writing one new class and we don't have to change anything else.

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3. Observer Pattern

Where:

• connect4.observer.GameObserver (interface)
• connect4.observer.ConsoleGameObserver (implementation) Why Connect4Game maintains a list of observers and notifies them when something happens : a move is made, someone wins, the game is a draw. This keeps game logic and display logic completely separate. Connect4Game never prints anything itself, it just announces events and observers decide what to do with them.

3. Builder Pattern

Where:

• connect4.builder.Connect4GameBuilder Why Setting up a game requires a board, two players, pieces, strategies, and a win strategy. The builder lets you configure all of this step by step through chained method calls and then call build() to get a fully assembled game. GameSetupDialog uses it to turn the user's UI selections into a ready-to-play Connect4Game.

3. Command Pattern

Where:

• connect4.command.GameCommand (interface)
• connect4.command.DropPieceCommand (implementation) Why Every move is wrapped in a DropPieceCommand that saves the game state before executing. If undo is called, it restores that saved state. SwingConnect4 keeps a stack of executed commands and clicking Undo pops the last one and reverts the board. This gives us undo support without putting any undo logic inside Connect4Game itself.

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Foundational Classes and Logic

The project contains fully implemented classes with meaningful logic:

Board Logic

• connect4.board.Board (interface)
• connect4.board.GridBoard (implementation)

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Game Logic

• connect4.controller.Connect4Game

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Player & Pieces

• connect4.player.Player (interface)
• connect4.player.HumanPlayer
• connect4.piece.GamePiece (interface)
• connect4.piece.RedPiece, BluePiece

Responsibilities:

• Represent players and their assigned pieces
• Provide piece symbols and color identity

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View

• connect4.view.ConsoleBoardView
• connect4.view.ConsoleBoardView
• connect4.view.SwingConnect4
• connect4.view.GameSetupDialog

Responsibilities:

• Displaying the board in the terminal

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Object-Oriented Principles

1. Coding to Abstractions

• Board
• Player
• GamePiece
• WinStrategy
• GameObserver

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2. Polymorphism

Polymorphism is demonstrated through:

• RedPiece and BluePiece implementing GamePiece
• HumanPlayer implementing Player
• StandardWinStrategy implementing WinStrategy
• ConsoleGameObserver implementing GameObserver

This allows the program to treat different implementations uniformly.

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3. Dependency Injection

Dependencies are passed into classes instead of being created inside them.

Example from Connect4Game:

 new Connect4Game(board, players, strategy);

How to Run

• Run SwingConnect4.main() to launch the GUI. A setup dialog will appear to choose your game mode and difficulty.
• Run Main.main() for the console version.