OOD 面向对象设计有很大的几率出现在小公司的面试上，在youtube上找了一个很好的教程来和大家分享一下。

问题： OOD 思想设计两人投掷硬币的游戏。

步骤一： 准备documentation

游戏介绍：随机选择一个玩家，令该玩家预测硬币的正反面，另一个玩家获得和第一个玩家相反的选项。开始投掷硬币，预测正确的赢。

Actors： 1. 玩家A 2. 玩家B 3. 硬币 4. 掷硬币游戏

根据以上信息我们可以画出object model. 这个决定我们要创建多少个实体类。

根据游戏规则以及流程，我们可以画出类图。

步骤二：代码实现

Player class.

public class Player {
	private String Name;
	private String CoinOption;
	public String[] coinValue = {"Heads","Tails"};
 	Player(String name){
		this.Name = name;
	}
	
	public String getCoinOption(){
		return this.CoinOption;
	}
	
	public void setCoinOption(String opponentFlip){
		this.CoinOption = (opponentFlip.equals("Heads"))?"Tails":"Heads";
	}
	
	public String getRandCoinOption(){
		int randNum = (Math.random()<0.5)?0:1;
		this.CoinOption = this.coinValue[randNum];
		return this.CoinOption;
	}
	
	public void didPlayerWin(String winningFlip){
		
		if(this.CoinOption.equals(winningFlip)){
			System.out.println(this.Name + " won with flip of " + this.CoinOption);
		}
		else
			System.out.println(this.Name + " lost " + this.CoinOption);
	}

}

public class Coin {
	private String coinOption = "";
	public String[] coinValue = {"Heads","Tails"};
	
	Coin(){
		int randNum = (Math.random() < 0.5)?0:1;
		this.coinOption = this.coinValue[randNum];
	}
	
	public String getCoinOption(){
		return this.coinOption;
	}

}

CoinGame Class

public class CoinGame {
	 Player[] players = new Player[2];
	 Coin theCoin = new Coin();
	 
	 CoinGame(String p1Name,String p2Name){
		 
		 players[0] = new Player(p1Name);
		 players[1] = new Player(p2Name);
	 }
	 
	 public void startGame(){
		 
		 int randNum = Math.random()<0.5?0:1;
		 String playersPick = players[randNum].getRandCoinOption();
		 
		 int opponentsIndex = (randNum == 1)?0:1;
		 players[opponentsIndex].setCoinOption(playersPick);
		 
		 String winningFlip = theCoin.getCoinOption();
		 
		 players[0].didPlayerWin(winningFlip);
		 players[1].didPlayerWin(winningFlip);
	 }

}

public class main {
	
	public static void main(String[] args){
		
		CoinGame theCoinGame = new CoinGame("Huazhe","meigtong");
		
		String userAnswer;
		
		do{
			
			theCoinGame.startGame();
			
			System.out.println("Play again?y/n");	
			Scanner input = new Scanner(System.in);
			userAnswer = input.nextLine();
		}while(userAnswer.equals("y"));
		
	}

}

学习心得：个人感觉 OOD 体现的更多的是对问题由大到小进行分割的思想，将大的问题进行简化成一部分模块( object )， 然后对各个模块之间的交流进行组合已达到解决问题的最终目的。