Java面向对象程序设计（五）--设计原则

消除代码复制的两个重要手段就是：父类和函数

评判一个程序是否优秀，主要是看类的设计

程序设计的目标是一系列通过明确的接口通信来协同工作的类。

在类的设计中，有两个重要的术语，耦合和聚合。

耦合：类与类之间的联系

 我们要努力获得低的耦合度，因为在一个紧耦合的结构中，对一个类的修改也需要对其他类的修改，是一件既费时又易出错的事情。

聚合：一个代码单元应该负责一个聚合的任务

 如果一个方法或类只负责一件定义明确的事情，那么就很有可能在另外不同的上下文环境中使用。

当程序某部分的代码需要改变时，在某个代码单元中很可能会找到所有需要改变的相关代码段。

再高层次的设计理念是优秀的代码要有可拓展性，

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可扩展性：代码的某些部分不需要经过修改就能适应将来可能的变化。

 翁恺老师太强辣！设计理念简直不要太棒，虽然看了几遍才懂

旧版本城堡游戏

package castle;

import java.util.Scanner;

public class Game {
    private Room currentRoom;
        
    public Game() 
    {
        createRooms();
    }

    private void createRooms()
    {
        Room outside, lobby, pub, study, bedroom;
      
        //	制造房间
        outside = new Room("城堡外");
        lobby = new Room("大堂");
        pub = new Room("小酒吧");
        study = new Room("书房");
        bedroom = new Room("卧室");
        
        //	初始化房间的出口
        outside.setExits(null, lobby, study, pub);
        lobby.setExits(null, null, null, outside);
        pub.setExits(null, outside, null, null);
        study.setExits(outside, bedroom, null, null);
        bedroom.setExits(null, null, null, study);

        currentRoom = outside;  //	从城堡门外开始
    }

    private void printWelcome() {
        System.out.println();
        System.out.println("欢迎来到城堡！");
        System.out.println("这是一个超级无聊的游戏。");
        System.out.println("如果需要帮助，请输入 'help' 。");
        System.out.println();
        System.out.println("现在你在" + currentRoom);
        System.out.print("出口有：");
        if(currentRoom.northExit != null)
            System.out.print("north ");
        if(currentRoom.eastExit != null)
            System.out.print("east ");
        if(currentRoom.southExit != null)
            System.out.print("south ");
        if(currentRoom.westExit != null)
            System.out.print("west ");
        System.out.println();
    }

    // 以下为用户命令

    private void printHelp() 
    {
        System.out.print("迷路了吗？你可以做的命令有：go bye help");
        System.out.println("如：\tgo east");
    }

    private void goRoom(String direction) 
    {
        Room nextRoom = null;
        if(direction.equals("north")) {
            nextRoom = currentRoom.northExit;
        }
        if(direction.equals("east")) {
            nextRoom = currentRoom.eastExit;
        }
        if(direction.equals("south")) {
            nextRoom = currentRoom.southExit;
        }
        if(direction.equals("west")) {
            nextRoom = currentRoom.westExit;
        }

        if (nextRoom == null) {
            System.out.println("那里没有门！");
        }
        else {
            currentRoom = nextRoom;
            System.out.println("你在" + currentRoom);
            System.out.print("出口有: ");
            if(currentRoom.northExit != null)
                System.out.print("north ");
            if(currentRoom.eastExit != null)
                System.out.print("east ");
            if(currentRoom.southExit != null)
                System.out.print("south ");
            if(currentRoom.westExit != null)
                System.out.print("west ");
            System.out.println();
        }
    }
	
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		Game game = new Game();
		game.printWelcome();

        while ( true ) {
        		String line = in.nextLine();
        		String[] words = line.split(" ");
        		if ( words[0].equals("help") ) {
        			game.printHelp();
        		} else if (words[0].equals("go") ) {
        			game.goRoom(words[1]);
        		} else if ( words[0].equals("bye") ) {
        			break;
        		}
        }
        
        System.out.println("感谢您的光临。再见！");
        in.close();
	}

}

package castle;

public class Room {
    public String description;
    public Room northExit;
    public Room southExit;
    public Room eastExit;
    public Room westExit;

    public Room(String description) 
    {
        this.description = description;
    }

    public void setExits(Room north, Room east, Room south, Room west) 
    {
        if(north != null)
            northExit = north;
        if(east != null)
            eastExit = east;
        if(south != null)
            southExit = south;
        if(west != null)
            westExit = west;
    }

    @Override
    public String toString()
    {
        return description;
    }
}

改良版本，亮瞎你二十年单身的十英寸大狗眼

可拓展性一流

package castle;

import java.util.HashMap;
import java.util.Scanner;

public class Game {
    private Room currentRoom;
    private HashMap<String, Handler> handlers = new HashMap<String, Handler>();//妙
    
    //把硬编码弄成框架    
    public Game() 
    {
    	handlers.put("bye", new HandlerBye(this));
    	handlers.put("help", new HandlerHelp(this));
    	handlers.put("go", new HandlerGo(this));
        createRooms();
    }

    private void createRooms()
    {
        Room outside, lobby, pub, study, bedroom, balcony , wineCeller;
      
        //	制造房间
        outside = new Room("城堡外");
        lobby = new Room("大堂");
        pub = new Room("小酒吧");
        study = new Room("书房");
        bedroom = new Room("卧室");
        balcony = new Room("阳台");
        wineCeller = new Room("酒窖");
        
        //	初始化房间的出口
        outside.setExit("west", pub);
        outside.setExit("east", lobby);
        outside.setExit("south", study);
        pub.setExit("east", outside);
        lobby.setExit("east", outside);
        study.setExit("north", outside);
        study.setExit("east", bedroom);
        bedroom.setExit("east", study);
        lobby.setExit("up", balcony);
        lobby.setExit("down", wineCeller);
        balcony.setExit("down", lobby);
        wineCeller.setExit("up", lobby);//酒窖哈哈
        
        currentRoom = outside;  //	从城堡门外开始
    }

    private void printWelcome() {
        System.out.println();
        System.out.println("欢迎来到城堡！");
        System.out.println("这是一个超级无聊的游戏。");
        System.out.println("如果需要帮助，请输入 'help' 。");
        System.out.println();
        showposition();
    }

    // 以下为用户命令
    
    
    public void showposition()
    {
    	System.out.println("你在" + currentRoom);
        System.out.print("出口有: ");
        System.out.println(currentRoom.getExitInfo());//接口不错，降低耦合
    }
    
    public void goRoom(String direction) 
    {
        Room nextRoom = currentRoom.getExit(direction);//接口降低耦合
        if (nextRoom == null) {
            System.out.println("那里没有门！");
        }
        else {
            currentRoom = nextRoom;
            showposition();
        }
    }
	//游戏运行代码
    public void play()
    {
		Scanner in = new Scanner(System.in);
    	while ( true ) {
     		String line = in.nextLine();
     		String[] words = line.split(" ");//读入方式你学到了吗
     		String value = "";
     		Handler handler = handlers.get(words[0]);
     		if(words.length>1)//如果不是go，那么传进去空字符串并无大碍
     		{
     			value = words[1];
     		}
     		if(handler != null)
     		{
     			handler.docmd(value);
     			if(handler.isBye())
     			{
     				break;
     			}
     		}
    	 }
         in.close();
    }
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		Game game = new Game();
		game.printWelcome();
		game.play();
        System.out.println("感谢您的光临。再见！");
	}

}


package castle;

import java.util.HashMap;

public class Room {
    private String description;
    private HashMap<String, Room> exits = new HashMap<String, Room>();
    
    public Room(String description) 
    {
        this.description = description;
    }
    
    public void setExit(String direction , Room room)//做成框架，不用像以前那样必须弄成参数表
    {
    	exits.put(direction, room);
    }

    @Override
    public String toString()
    {
        return description;
    }
    public String getExitInfo()//接口降低与Game的耦合
    {
    	StringBuffer sb = new StringBuffer();//学到了，Java中StringBuffer是类似于c++中存放String的vector
    	for(String direction : exits.keySet())//for-each 遍历表中可触及到的地方并加入到字符串中（感觉有点像BFS的第一层，但是这个高效多了哇）
    	{
    		sb.append(direction);
    		sb.append(' ');
    	}
    	return sb.toString();
    }
    public Room getExit(String direction)
    {
    	return exits.get(direction);
    }
}


package castle;

public class Handler {
	protected Game game;
	
	public Handler(Game game) {
		this.game = game;
	}
	public void docmd(String word) {}
	public boolean isBye()
	{
		return false;
	}
}


package castle;

public class HandlerBye extends Handler{
	
	public HandlerBye(Game game) {
		super(game);
		this.game = game;
	}
	@Override
	public boolean isBye() {
		return true;
	}
	
}


package castle;

public class HandlerHelp extends Handler {
	
	public HandlerHelp(Game game) {
		super(game);
		this.game = game;
	}
	@Override
	public void docmd(String word) {
		System.out.println("迷路了吗？你可以做的命令有：go bye help");
        System.out.println("如：\tgo east");
	}
	
}


package castle;

public class HandlerGo extends Handler {
	
	public HandlerGo(Game game) {
		super(game);
		this.game = game;
	}
	@Override
	public void docmd(String word) {
		game.goRoom(word);
	}
	
}

 虽然是个无聊的小游戏，不过这个设计理念是很重要的

下面是运行结果

nice！