MOOC 浙江大学 面向对象程序设计-Java笔记（5）

------------翁恺老师授课
第五次课程 设计原则
课程核心部分体现在程序的优化中，从繁琐到简洁！！！

1. 避免大量的代码复制
2. 避免大量的if-else
3. 类中成员变量请设置成私有访问属性

消除代码复制：

1.函数封装

  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 void showPrompt(Room cRoom) {
    	System.out.println("现在你在" + cRoom);
    	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();
    	}
    }

2.父类
代码的耦合与聚合
耦合：类与类之间应该保持距离，越远越好。
聚合：针对类与方法，与程序中一个单独的单元所承担的任务的数量和种类相对应有关。一个方法只负责一件定义明确的事情。

可扩展性

问题： 在程序中进行硬编码，很多类的硬编码是基于字符界面，通过终端进行输入输出。
解决方案： 从程序中识别出框架和数据，以代码实现框架，将部分功能以数据的方式加载（容器）。擅于使用容器来解决问题，实现灵活性。

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;
    }
}

    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();
        }
    }

改造后

public class Room {
    private String description;
    private HashMap<String, Room> exits = new HashMap<String, Room>();

Public String getExits () {
    	StringBuffer sb = new StringBuffer();
    	for(String dir: exits.keySet()) {
    		sb.append(dir);
    		sb.append(' ');
    	}
    	return sb.toString();
    }

public void showPrompt(Room cRoom) {
    System.out.println("现在你在" + cRoom);
    System.out.print("出口有: ");
    ------
    String exits = cRoom.getExits();
    System.out.println(exits);
    -------
    System.out.println();
 }