Questions and Exercises: Classes问题和练习：类

Questions问题

1. Consider the following class:考虑下面的类：

   public class IdentifyMyParts {
       public static int x = 7; 
       public int y = 3; 
   }

   1. What are the class variables?什么是类变量？x

   2. What are the instance variables?实例变量是什么？y

   3. What is the output from the following code:以下代码的输出是什么：

      IdentifyMyParts a = new IdentifyMyParts();
      IdentifyMyParts b = new IdentifyMyParts();
      a.y = 5;
      b.y = 6;
      a.x = 1;
      b.x = 2;
      System.out.println("a.y = " + a.y);
      System.out.println("b.y = " + b.y);
      System.out.println("a.x = " + a.x);
      System.out.println("b.x = " + b.x);
      System.out.println("IdentifyMyParts.x = " + IdentifyMyParts.x);

Exercises练习

1. Write a class whose instances represent a single playing card from a deck of cards.编写一个类，其实例表示一副牌中的一张扑克牌。Playing cards have two distinguishing properties: rank and suit.扑克牌有两个显著的特性：等级和套装。Be sure to keep your solution as you will be asked to rewrite it in Enum Types.请确保保留您的解决方案，因为您将被要求在枚举类型中重写它。

   ---

   Hint:提示： 

   You can use the assert statement to check your assignments.您可以使用assert语句检查分配。You write:你写道：

   assert (boolean expression to test);

   If the boolean expression is false, you will get an error message.如果布尔表达式为false，则会收到错误消息。For example,例如

   assert toString(ACE) == "Ace";

   should return true, so there will be no error message.应返回true，因此不会出现错误消息。

   If you use the assert statement, you must run your program with the ea flag:如果使用assert语句，则必须使用ea标志运行程序：

   java -ea YourProgram.class

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2. Write a class whose instances represent a full deck of cards.编写一个类，其实例表示一整套卡片。You should also keep this solution.您还应该保留此解决方案。

3. Write a small program to test your deck and card classes.编写一个小程序来测试你的卡片组和卡片类。The program can be as simple as creating a deck of cards and displaying its cards.该程序可以简单到创建一副卡片并显示其卡片。

Check your answers.检查你的答案。