201772020113李清华《面向对象程序设计（java）》第十周学习总结

1、实验目的与要求

(1) 理解泛型概念；

(2) 掌握泛型类的定义与使用；

(3) 掌握泛型方法的声明与使用；

(4) 掌握泛型接口的定义与实现；

(5)了解泛型程序设计，理解其用途。

2、实验内容和步骤

实验1：导入第8章示例程序，测试程序并进行代码注释。

测试程序1：

l 编辑、调试、运行教材311、312页 代码，结合程序运行结果理解程序；

l 在泛型类定义及使用代码处添加注释；

l 掌握泛型类的定义及使用。

 1 package pair1;
 2 
 3 /**
 4  * @version 1.00 2004-05-10
 5  * @author Cay Horstmann
 6  */
 7 public class Pair<T>//Pair类引入了一个类型变量T，用尖括号括起来
 8  
 9 {
10    private T first;
11    private T second;
12    //指方法的返回类型以及域和局部变量的类型
13    public Pair() { first = null; second = null; }
14    public Pair(T first, T second) { this.first = first;  this.second = second; }
15 
16    public T getFirst() { return first; }
17    public T getSecond() { return second; }
18 
19    public void setFirst(T newValue) { first = newValue; }
20    public void setSecond(T newValue) { second = newValue; }
21 }

 1 package pair1;
 2 
 3 /**
 4  * @version 1.01 2012-01-26
 5  * @author Cay Horstmann
 6  */
 7 public class PairTest1
 8 {
 9    public static void main(String[] args)
10    {
11       String[] words = { "Mary", "had", "a", "little", "lamb" };
12       Pair<String> mm = ArrayAlg.minmax(words);
13       System.out.println("min = " + mm.getFirst());
14       System.out.println("max = " + mm.getSecond());
15    }
16 }
17 
18 class ArrayAlg
19 {
20    /**
21     * Gets the minimum and maximum of an array of strings.
22     * @param a an array of strings
23     * @return a pair with the min and max value, or null if a is null or empty
24     */
25    public static Pair<String> minmax(String[] a)//使用静态方法来用泛型方法
26    {
27       if (a == null || a.length == 0) return null;
28       String min = a[0];
29       String max = a[0];
30       for (int i = 1; i < a.length; i++)
31       {
32          if (min.compareTo(a[i]) > 0) min = a[i];
33          if (max.compareTo(a[i]) < 0) max = a[i];
34       }
35       return new Pair<>(min, max);
36    }
37 }

测试程序2：

l 编辑、调试运行教材315页 PairTest2，结合程序运行结果理解程序；

l 在泛型程序设计代码处添加相关注释；

l 掌握泛型方法、泛型变量限定的定义及用途。

 1 package pair2;
 2 
 3 import java.time.*;
 4 
 5 /**
 6  * @version 1.02 2015-06-21
 7  * @author Cay Horstmann
 8  */
 9 public class PairTest2
10 {
11    public static void main(String[] args)
12    {
13       LocalDate[] birthdays = 
14          { 
15             LocalDate.of(1906, 12, 9), // G. Hopper
16             LocalDate.of(1815, 12, 10), // A. Lovelace
17             LocalDate.of(1903, 12, 3), // J. von Neumann
18             LocalDate.of(1910, 6, 22), // K. Zuse
19          };
20       Pair<LocalDate> mm = ArrayAlg.minmax(birthdays);
21       System.out.println("min = " + mm.getFirst());
22       System.out.println("max = " + mm.getSecond());
23    }
24 }
25 
26 class ArrayAlg
27 {
28    /**
29       Gets the minimum and maximum of an array of objects of type T.
30       @param a an array of objects of type T
31       @return a pair with the min and max value, or null if a is 
32       null or empty
33    */
34    public static <T extends Comparable> Pair<T> minmax(T[] a) 
35    {
36       if (a == null || a.length == 0) return null;
37       T min = a[0];
38       T max = a[0];
39       for (int i = 1; i < a.length; i++)
40       {
41          if (min.compareTo(a[i]) > 0) min = a[i];
42          if (max.compareTo(a[i]) < 0) max = a[i];
43       }
44       return new Pair<>(min, max);
45    }
46 }

package pair2;

/**
 * @version 1.00 2004-05-10
 * @author Cay Horstmann
 */
public class Pair<T> 
{
   private T first;
   private T second;

   public Pair() { first = null; second = null; }
   public Pair(T first, T second) { this.first = first;  this.second = second; }

   public T getFirst() { return first; }
   public T getSecond() { return second; }

   public void setFirst(T newValue) { first = newValue; }
   public void setSecond(T newValue) { second = newValue; }
}

测试程序3：

l 用调试运行教材335页 PairTest3，结合程序运行结果理解程序；

l 了解通配符类型的定义及用途。

package pair3;

/**
 * @version 1.01 2012-01-26
 * @author Cay Horstmann
 */
public class PairTest3
{
   public static void main(String[] args)
   {
      Manager ceo = new Manager("Gus Greedy", 800000, 2003, 12, 15);
      Manager cfo = new Manager("Sid Sneaky", 600000, 2003, 12, 15);
      Pair<Manager> buddies = new Pair<>(ceo, cfo);      
      printBuddies(buddies);

      ceo.setBonus(1000000);
      cfo.setBonus(500000);
      Manager[] managers = { ceo, cfo };

      Pair<Employee> result = new Pair<>();
      minmaxBonus(managers, result);
      System.out.println("first: " + result.getFirst().getName() 
         + ", second: " + result.getSecond().getName());
      maxminBonus(managers, result);
      System.out.println("first: " + result.getFirst().getName() 
         + ", second: " + result.getSecond().getName());
   }

   public static void printBuddies(Pair<? extends Employee> p)
   {
      Employee first = p.getFirst();
      Employee second = p.getSecond();
      System.out.println(first.getName() + " and " + second.getName() + " are buddies.");
   }

   public static void minmaxBonus(Manager[] a, Pair<? super Manager> result)
   {
      if (a.length == 0) return;
      Manager min = a[0];
      Manager max = a[0];
      for (int i = 1; i < a.length; i++)
      {
         if (min.getBonus() > a[i].getBonus()) min = a[i];
         if (max.getBonus() < a[i].getBonus()) max = a[i];
      }
      result.setFirst(min);
      result.setSecond(max);
   }

   public static void maxminBonus(Manager[] a, Pair<? super Manager> result)
   {
      minmaxBonus(a, result);
      PairAlg.swapHelper(result); // OK--swapHelper captures wildcard type
   }
   // Can't write public static <T super manager> ...
}

class PairAlg
{
   public static boolean hasNulls(Pair<?> p)
   {
      return p.getFirst() == null || p.getSecond() == null;
   }

   public static void swap(Pair<?> p) { swapHelper(p); }

   public static <T> void swapHelper(Pair<T> p)
   {
      T t = p.getFirst();
      p.setFirst(p.getSecond());
      p.setSecond(t);
   }
}

package pair3;

/**
 * @version 1.00 2004-05-10
 * @author Cay Horstmann
 */
public class Pair<T> 
{
   private T first;
   private T second;

   public Pair() { first = null; second = null; }
   public Pair(T first, T second) { this.first = first;  this.second = second; }

   public T getFirst() { return first; }
   public T getSecond() { return second; }

   public void setFirst(T newValue) { first = newValue; }
   public void setSecond(T newValue) { second = newValue; }
}

package pair3;

import java.time.*;

public class Employee
{  
   private String name;
   private double salary;
   private LocalDate hireDay;

   public Employee(String name, double salary, int year, int month, int day)
   {
      this.name = name;
      this.salary = salary;
      hireDay = LocalDate.of(year, month, day);
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {  
      return salary;
   }

   public LocalDate getHireDay()
   {  
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {  
      double raise = salary * byPercent / 100;
      salary += raise;
   }
}

package pair3;

public class Manager extends Employee
{  
   private double bonus;

   /**
      @param name the employee's name
      @param salary the salary
      @param year the hire year
      @param month the hire month
      @param day the hire day
   */
   public Manager(String name, double salary, int year, int month, int day)
   {  
      super(name, salary, year, month, day);
      bonus = 0;
   }

   public double getSalary()
   { 
      double baseSalary = super.getSalary();
      return baseSalary + bonus;
   }

   public void setBonus(double b)
   {  
      bonus = b;
   }

   public double getBonus()
   {  
      return bonus;
   }
}

实验2：编程练习：

编程练习1：实验九编程题总结

l 实验九编程练习1总结（从程序总体结构说明、模块说明，目前程序设计存在的困难与问题三个方面阐述）。

  1 package test1;
  2 
  3 import java.io.BufferedReader;
  4 import java.io.File;
  5 import java.io.FileInputStream;
  6 import java.io.FileNotFoundException;
  7 import java.io.IOException;
  8 import java.io.InputStreamReader;
  9 import java.util.ArrayList;
 10 import java.util.Collections;
 11 import java.util.Scanner;
 12 
 13 public class Main{
 14     private static ArrayList<Student> studentlist;
 15     public static void main(String[] args) {
 16         studentlist = new ArrayList<>();
 17         Scanner scanner = new Scanner(System.in);
 18         File file = new File("F:\身份证号.txt");
 19         try {
 20             FileInputStream fis = new FileInputStream(file);
 21             BufferedReader in = new BufferedReader(new InputStreamReader(fis));
 22             String temp = null;
 23             while ((temp = in.readLine()) != null) {
 24                 
 25                 Scanner linescanner = new Scanner(temp);
 26                 
 27                 linescanner.useDelimiter(" ");    
 28                 String name = linescanner.next();
 29                 String number = linescanner.next();
 30                 String sex = linescanner.next();
 31                 String age = linescanner.next();
 32                 String province =linescanner.nextLine();
 33                 Student student = new Student();
 34                 student.setName(name);
 35                 student.setnumber(number);
 36                 student.setsex(sex);
 37                 int a = Integer.parseInt(age);
 38                 student.setage(a);
 39                 student.setprovince(province);
 40                 studentlist.add(student);
 41 
 42             }
 43         } catch (FileNotFoundException e) {
 44             System.out.println("学生信息文件找不到");
 45             e.printStackTrace();
 46         } catch (IOException e) {
 47             System.out.println("学生信息文件读取错误");
 48             e.printStackTrace();
 49         }
 50         boolean isTrue = true;
 51         while (isTrue) {
 52             System.out.println("选择你的操作，输入正确格式的选项");
 53             System.out.println("A.按姓名字典排序");
 54             System.out.println("B.输出年龄最大和年龄最小的人");
 55             System.out.println("C.寻找老乡");
 56             System.out.println("D.寻找年龄相近的人");
 57             System.out.println("F.退出");
 58             String m = scanner.next();
 59             switch (m) {
 60             case "A":
 61                 Collections.sort(studentlist);              
 62                 System.out.println(studentlist.toString());
 63                 break;
 64             case "B":
 65                  int max=0,min=100;
 66                  int j,k1 = 0,k2=0;
 67                  for(int i=1;i<studentlist.size();i++)
 68                  {
 69                      j=studentlist.get(i).getage();
 70                  if(j>max)
 71                  {
 72                      max=j; 
 73                      k1=i;
 74                  }
 75                  if(j<min)
 76                  {
 77                    min=j; 
 78                    k2=i;
 79                  }
 80                  
 81                  }  
 82                  System.out.println("年龄最大："+studentlist.get(k1));
 83                  System.out.println("年龄最小："+studentlist.get(k2));
 84                 break;
 85             case "C":
 86                  System.out.println("老家?");
 87                  String find = scanner.next();        
 88                  String place=find.substring(0,3);
 89                  for (int i = 0; i <studentlist.size(); i++) 
 90                  {
 91                      if(studentlist.get(i).getprovince().substring(1,4).equals(place)) 
 92                          System.out.println("老乡"+studentlist.get(i));
 93                  }             
 94                  break;
 95                  
 96             case "D":
 97                 System.out.println("年龄：");
 98                 int yourage = scanner.nextInt();
 99                 int near=agenear(yourage);
100                 int value=yourage-studentlist.get(near).getage();
101                 System.out.println(""+studentlist.get(near));
102                 break;
103             case "F":
104                 isTrue = false;
105                 System.out.println("退出程序!");
106                 break;
107                 default:
108                 System.out.println("输入有误");
109 
110             }
111         }
112     }
113         public static int agenear(int age) {      
114         int j=0,min=53,value=0,k=0;
115          for (int i = 0; i < studentlist.size(); i++)
116          {
117              value=studentlist.get(i).getage()-age;
118              if(value<0) value=-value; 
119              if (value<min) 
120              {
121                 min=value;
122                 k=i;
123              } 
124           }    
125          return k;         
126       }
127 
128 }

 1 package test1;
 2 
 3 public class Student implements Comparable<Student> {
 4 
 5     private String name;
 6     private String number ;
 7     private String sex ;
 8     private int age;
 9     private String province;
10    
11     public String getName() {
12         return name;
13     }
14     public void setName(String name) {
15         this.name = name;
16     }
17     public String getnumber() {
18         return number;
19     }
20     public void setnumber(String number) {
21         this.number = number;
22     }
23     public String getsex() {
24         return sex ;
25     }
26     public void setsex(String sex ) {
27         this.sex =sex ;
28     }
29     public int getage() {
30 
31         return age;
32         }
33         public void setage(int age) {
34             // int a = Integer.parseInt(age);
35         this.age= age;
36         }
37 
38     public String getprovince() {
39         return province;
40     }
41     public void setprovince(String province) {
42         this.province=province ;
43     }
44 
45     public int compareTo(Student o) {
46        return this.name.compareTo(o.getName());
47     }
48 
49     public String toString() {
50         return  name+"	"+sex+"	"+age+"	"+number+"	"+province+"
";
51     }    
52 }

总体结构：

程序有一个主类和一个子类。

模块说明：

主类涉及到对文件的读入操作，所以要用try...catch语句进行异常处理。还有选择语句。

子类是对接口Comparable的实现。主要用来返回学生的信息。

目前程序设计的困难：

对文件的读写操作不熟悉，不知道如何进行排序以及查找。

l 实验九编程练习2总结（从程序总体结构说明、模块说明，目前程序设计存在的困难与问题三个方面阐述）。

 1 package shiyan;
 2 import java.util.Scanner;
 3 import java.io.PrintWriter;
 4 
 5 public class Main {
 6     public static void main(String[] args) throws Exception{
 7         Scanner in=new Scanner(System.in);
 8         PrintWriter output=new PrintWriter("E:/test.txt");
 9         int sum=0;
10         jisuanji js=new jisuanji();
11         for (int i = 0; i < 10; i++) {
12             int a = (int) Math.round(Math.random() * 100);
13             int b = (int) Math.round(Math.random() * 100);
14             int n = (int) Math.round(Math.random() * 3);
15             
16             switch(n)
17                {
18                case 1:
19                    System.out.println(a+"/"+b+"=");
20                    while(b==0){  
21                        b = (int) Math.round(Math.random() * 100); 
22                        }
23                    double c = in.nextDouble();
24                    output.println(a+"/"+b+"="+c);
25                    if (c == js.chu(a,b)) {
26                        sum += 10;
27                        System.out.println("答案正确");
28                    }
29                    else {
30                        System.out.println("答案错误");
31                    }
32                 
33                    break;
34                 
35                case 2:
36                    System.out.println(a+"*"+b+"=");
37                    int c1 = in.nextInt();
38                    output.println(a+"*"+b+"="+c1);
39                    if (c1 == js.chen(a, b)) {
40                        sum += 10;
41                        System.out.println("答案正确");
42                    }
43                    else {
44                        System.out.println("答案错误");
45                    }
46                    break;
47                case 3:
48                    System.out.println(a+"+"+b+"=");
49                    int c2 = in.nextInt();
50                    output.println(a+"+"+b+"="+c2);
51                    if (c2 == js.jia(a, b)) {
52                        sum += 10;
53                        System.out.println("答案正确");
54                    }
55                    else {
56                        System.out.println("答案错误");
57                    }
58                    
59                    break ;
60                case 4:
61                    System.out.println(a+"-"+b+"=");
62                    int c3 = in.nextInt();
63                    output.println(a+"-"+b+"="+c3);
64                    if (c3 == js.jian(a,b)) {
65                        sum += 10;
66                        System.out.println("答案正确");
67                    }
68                    else {
69                        System.out.println("答案错误");
70                    }
71                    break ;
72 
73                    } 
74         
75               }
76             System.out.println("成绩"+sum);
77             output.println("成绩:"+sum);
78             output.close();
79         }
80     }

View Code

 1 package shiyan;
 2 
 3 public class jisuanji {
 4     private int a;
 5     private int b;
 6     public int jia(int a,int b)
 7     {
 8         return a+b;
 9     }
10     public int jian(int a,int b)
11     {
12         return a-b;
13     }
14     public int chen(int a,int b)
15     {
16         return a*b;
17     }
18     public int chu(int a,int b)
19     {
20         if(b==0) 
21         {
22             return 0;
23         }
24         else 
25             return a/b;
26     }
27 }

View Code

总体结构：有一个主类和一个子类。

模块说明：主类里涉及文件的输出和异常处理，子类是实现计算器功能的算法。

困难：不熟悉写出到文件的操作，导致程序编写困难。生成的减法和除法运算题不适应小学生的能力。

编程练习2：采用泛型程序设计技术改进实验九编程练习2，使之可处理实数四则运算，其他要求不变。

 1 package shiyan;
 2 import java.util.Scanner;
 3 import java.io.FileNotFoundException;
 4 import java.io.PrintWriter;
 5 
 6 public class Main {
 7     public static void main(String[] args) {
 8         Scanner in=new Scanner(System.in);
 9         PrintWriter output = null;
10         try {
11             output = new PrintWriter("E:/test.txt");
12         } catch (FileNotFoundException e) {
13             // TODO 自动生成的 catch 块
14             System.out.println("文件输出失败");
15             e.printStackTrace();
16         }
17         int sum=0;
18         jisuanji js=new jisuanji();
19         for (int i = 0; i < 10; i++) {
20             int a = (int) Math.round(Math.random() * 100);
21             int b = (int) Math.round(Math.random() * 100);
22             int n = (int) Math.round(Math.random() * 4 );
23             
24             switch(n)
25                {
26                case 1:
27                    System.out.println(a+"/"+b+"=");
28                    while(b==0){  
29                        b = (int) Math.round(Math.random() * 100); 
30                        }
31                    while(a%b!=0) {
32                        a = (int) Math.round(Math.random() * 100);
33                        b = (int) Math.round(Math.random() * 100);
34                    }
35                    double c = in.nextDouble();
36                    output.println(a+"/"+b+"="+c);
37                    if (c == js.chu(a,b)) {
38                        sum += 10;
39                        System.out.println("答案正确");
40                    }
41                    else {
42                        System.out.println("答案错误");
43                    }
44                 
45                    break;
46                 
47                case 2:
48                    System.out.println(a+"*"+b+"=");
49                    int c1 = in.nextInt();
50                    output.println(a+"*"+b+"="+c1);
51                    if (c1 == js.chen(a, b)) {
52                        sum += 10;
53                        System.out.println("答案正确");
54                    }
55                    else {
56                        System.out.println("答案错误");
57                    }
58                    break;
59                case 3:
60                    System.out.println(a+"+"+b+"=");
61                    int c2 = in.nextInt();
62                    output.println(a+"+"+b+"="+c2);
63                    if (c2 == js.jia(a, b)) {
64                        sum += 10;
65                        System.out.println("答案正确");
66                    }
67                    else {
68                        System.out.println("答案错误");
69                    }
70                    
71                    break ;
72                case 4:
73                    System.out.println(a+"-"+b+"=");
74                    while(a<b) {
75                        a = (int) Math.round(Math.random() * 100);
76                        b = (int) Math.round(Math.random() * 100);
77                    }
78                    int c3 = in.nextInt();
79                    output.println(a+"-"+b+"="+c3);
80                    if (c3 == js.jian(a,b)) {
81                        sum += 10;
82                        System.out.println("答案正确");
83                    }
84                    else {
85                        System.out.println("答案错误");
86                    }
87                    break ;
88 
89                    } 
90         
91               }
92             System.out.println("成绩"+sum);
93             output.println("成绩:"+sum);
94             output.close();
95         }
96     }

View Code

 1 package shiyan;
 2 
 3 public class jisuanji<T> {
 4     private T a;
 5     private T b;
 6     public jisuanji() {
 7         a=null;
 8         b=null;
 9     }
10     public jisuanji(T a,T b) {
11         this.a=a;
12         this.b=b;
13     }
14     public int jia(int a,int b)
15     {
16         return a+b;
17     }
18     public int jian(int a,int b)
19     {
20         return a-b;
21     }
22     public int chen(int a,int b)
23     {
24         return a*b;
25     }
26     public int chu(int a,int b)
27     {
28         if(b!=0&&a%b==0) 
29             return a/b;
30         else 
31             return 0;
32     }
33 }

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实验总结：

这次实验加深了对实验9编程题的理解，改进了其中的错误。学会了泛型类的设计，但是通配符还是有些不理解的地方。