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。

 package pair1;

 /**
  * @version 1.00 2004-05-10
  * @author Cay Horstmann
  */
 public class Pair<T>//Pair类引入了一个类型变量T，用尖括号括起来

 {
    private T first;
    private T second;
    //指方法的返回类型以及域和局部变量的类型
    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 pair1;

 /**
  * @version 1.01 2012-01-26
  * @author Cay Horstmann
  */
 public class PairTest1
 {
    public static void main(String[] args)
    {
       String[] words = { "Mary", "had", "a", "little", "lamb" };
       Pair<String> mm = ArrayAlg.minmax(words);
       System.out.println("min = " + mm.getFirst());
       System.out.println("max = " + mm.getSecond());
    }
 }

 class ArrayAlg
 {
    /**
     * Gets the minimum and maximum of an array of strings.
     * @param a an array of strings
     * @return a pair with the min and max value, or null if a is null or empty
     */
    public static Pair<String> minmax(String[] a)//使用静态方法来用泛型方法
    {
       if (a == null || a.length == 0) return null;
       String min = a[0];
       String max = a[0];
       for (int i = 1; i < a.length; i++)
       {
          if (min.compareTo(a[i]) > 0) min = a[i];
          if (max.compareTo(a[i]) < 0) max = a[i];
       }
       return new Pair<>(min, max);
    }
 }

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。

 package pair2;

 import java.time.*;

 /**
  * @version 1.02 2015-06-21
  * @author Cay Horstmann
  */
 public class PairTest2
 {
    public static void main(String[] args)
    {
       LocalDate[] birthdays =
          {
             LocalDate.of(1906, 12, 9), // G. Hopper
             LocalDate.of(1815, 12, 10), // A. Lovelace
             LocalDate.of(1903, 12, 3), // J. von Neumann
             LocalDate.of(1910, 6, 22), // K. Zuse
          };
       Pair<LocalDate> mm = ArrayAlg.minmax(birthdays);
       System.out.println("min = " + mm.getFirst());
       System.out.println("max = " + mm.getSecond());
    }
 }

 class ArrayAlg
 {
    /**
       Gets the minimum and maximum of an array of objects of type T.
       @param a an array of objects of type T
       @return a pair with the min and max value, or null if a is
       null or empty
    */
    public static <T extends Comparable> Pair<T> minmax(T[] a)
    {
       if (a == null || a.length == 0) return null;
       T min = a[0];
       T max = a[0];
       for (int i = 1; i < a.length; i++)
       {
          if (min.compareTo(a[i]) > 0) min = a[i];
          if (max.compareTo(a[i]) < 0) max = a[i];
       }
       return new Pair<>(min, max);
    }
 }

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）。

 package test1;

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Scanner;

 public class Main{
     private static ArrayList<Student> studentlist;
     public static void main(String[] args) {
         studentlist = new ArrayList<>();
         Scanner scanner = new Scanner(System.in);
         File file = new File("F:\\身份证号.txt");
         try {
             FileInputStream fis = new FileInputStream(file);
             BufferedReader in = new BufferedReader(new InputStreamReader(fis));
             String temp = null;
             while ((temp = in.readLine()) != null) {

                 Scanner linescanner = new Scanner(temp);

                 linescanner.useDelimiter(" ");
                 String name = linescanner.next();
                 String number = linescanner.next();
                 String sex = linescanner.next();
                 String age = linescanner.next();
                 String province =linescanner.nextLine();
                 Student student = new Student();
                 student.setName(name);
                 student.setnumber(number);
                 student.setsex(sex);
                 int a = Integer.parseInt(age);
                 student.setage(a);
                 student.setprovince(province);
                 studentlist.add(student);

             }
         } catch (FileNotFoundException e) {
             System.out.println("学生信息文件找不到");
             e.printStackTrace();
         } catch (IOException e) {
             System.out.println("学生信息文件读取错误");
             e.printStackTrace();
         }
         boolean isTrue = true;
         while (isTrue) {
             System.out.println("选择你的操作，输入正确格式的选项");
             System.out.println("A.按姓名字典排序");
             System.out.println("B.输出年龄最大和年龄最小的人");
             System.out.println("C.寻找老乡");
             System.out.println("D.寻找年龄相近的人");
             System.out.println("F.退出");
             String m = scanner.next();
             switch (m) {
             case "A":
                 Collections.sort(studentlist);
                 System.out.println(studentlist.toString());
                 break;
             case "B":
                  int max=0,min=100;
                  int j,k1 = 0,k2=0;
                  for(int i=1;i<studentlist.size();i++)
                  {
                      j=studentlist.get(i).getage();
                  if(j>max)
                  {
                      max=j;
                      k1=i;
                  }
                  if(j<min)
                  {
                    min=j;
                    k2=i;
                  }

                  }
                  System.out.println("年龄最大："+studentlist.get(k1));
                  System.out.println("年龄最小："+studentlist.get(k2));
                 break;
             case "C":
                  System.out.println("老家?");
                  String find = scanner.next();
                  String place=find.substring(0,3);
                  for (int i = 0; i <studentlist.size(); i++)
                  {
                      if(studentlist.get(i).getprovince().substring(1,4).equals(place))
                          System.out.println("老乡"+studentlist.get(i));
                  }
                  break;

             case "D":
                 System.out.println("年龄：");
                 int yourage = scanner.nextInt();
                 int near=agenear(yourage);
                 int value=yourage-studentlist.get(near).getage();
                 System.out.println(""+studentlist.get(near));
                 break;
             case "F":
                 isTrue = false;
                 System.out.println("退出程序!");
                 break;
                 default:
                 System.out.println("输入有误");

             }
         }
     }
         public static int agenear(int age) {
         int j=0,min=53,value=0,k=0;
          for (int i = 0; i < studentlist.size(); i++)
          {
              value=studentlist.get(i).getage()-age;
              if(value<0) value=-value;
              if (value<min)
              {
                 min=value;
                 k=i;
              }
           }
          return k;
       }

 }

 package test1;

 public class Student implements Comparable<Student> {

     private String name;
     private String number ;
     private String sex ;
     private int age;
     private String province;

     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public String getnumber() {
         return number;
     }
     public void setnumber(String number) {
         this.number = number;
     }
     public String getsex() {
         return sex ;
     }
     public void setsex(String sex ) {
         this.sex =sex ;
     }
     public int getage() {

         return age;
         }
         public void setage(int age) {
             // int a = Integer.parseInt(age);
         this.age= age;
         }

     public String getprovince() {
         return province;
     }
     public void setprovince(String province) {
         this.province=province ;
     }

     public int compareTo(Student o) {
        return this.name.compareTo(o.getName());
     }

     public String toString() {
         return  name+"\t"+sex+"\t"+age+"\t"+number+"\t"+province+"\n";
     }
 }

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）。

 package shiyan;
 import java.util.Scanner;
 import java.io.PrintWriter;

 public class Main {
     public static void main(String[] args) throws Exception{
         Scanner in=new Scanner(System.in);
         PrintWriter output=new PrintWriter("E:/test.txt");
         int sum=0;
         jisuanji js=new jisuanji();
         for (int i = 0; i < 10; i++) {
             int a = (int) Math.round(Math.random() * 100);
             int b = (int) Math.round(Math.random() * 100);
             int n = (int) Math.round(Math.random() * 3);

             switch(n)
                {
                case 1:
                    System.out.println(a+"/"+b+"=");
                    while(b==0){
                        b = (int) Math.round(Math.random() * 100);
                        }
                    double c = in.nextDouble();
                    output.println(a+"/"+b+"="+c);
                    if (c == js.chu(a,b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }

                    break;

                case 2:
                    System.out.println(a+"*"+b+"=");
                    int c1 = in.nextInt();
                    output.println(a+"*"+b+"="+c1);
                    if (c1 == js.chen(a, b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }
                    break;
                case 3:
                    System.out.println(a+"+"+b+"=");
                    int c2 = in.nextInt();
                    output.println(a+"+"+b+"="+c2);
                    if (c2 == js.jia(a, b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }

                    break ;
                case 4:
                    System.out.println(a+"-"+b+"=");
                    int c3 = in.nextInt();
                    output.println(a+"-"+b+"="+c3);
                    if (c3 == js.jian(a,b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }
                    break ;

                    } 

               }
             System.out.println("成绩"+sum);
             output.println("成绩:"+sum);
             output.close();
         }
     }

 package shiyan;

 public class jisuanji {
     private int a;
     private int b;
     public int jia(int a,int b)
     {
         return a+b;
     }
     public int jian(int a,int b)
     {
         return a-b;
     }
     public int chen(int a,int b)
     {
         return a*b;
     }
     public int chu(int a,int b)
     {
         if(b==0)
         {
             return 0;
         }
         else
             return a/b;
     }
 }

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。

 package shiyan;
 import java.util.Scanner;
 import java.io.FileNotFoundException;
 import java.io.PrintWriter;

 public class Main {
     public static void main(String[] args) {
         Scanner in=new Scanner(System.in);
         PrintWriter output = null;
         try {
             output = new PrintWriter("E:/test.txt");
         } catch (FileNotFoundException e) {
             // TODO 自动生成的 catch 块
             System.out.println("文件输出失败");
             e.printStackTrace();
         }
         int sum=0;
         jisuanji js=new jisuanji();
         for (int i = 0; i < 10; i++) {
             int a = (int) Math.round(Math.random() * 100);
             int b = (int) Math.round(Math.random() * 100);
             int n = (int) Math.round(Math.random() * 4 );

             switch(n)
                {
                case 1:
                    System.out.println(a+"/"+b+"=");
                    while(b==0){
                        b = (int) Math.round(Math.random() * 100);
                        }
                    while(a%b!=0) {
                        a = (int) Math.round(Math.random() * 100);
                        b = (int) Math.round(Math.random() * 100);
                    }
                    double c = in.nextDouble();
                    output.println(a+"/"+b+"="+c);
                    if (c == js.chu(a,b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }

                    break;

                case 2:
                    System.out.println(a+"*"+b+"=");
                    int c1 = in.nextInt();
                    output.println(a+"*"+b+"="+c1);
                    if (c1 == js.chen(a, b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }
                    break;
                case 3:
                    System.out.println(a+"+"+b+"=");
                    int c2 = in.nextInt();
                    output.println(a+"+"+b+"="+c2);
                    if (c2 == js.jia(a, b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }

                    break ;
                case 4:
                    System.out.println(a+"-"+b+"=");
                    while(a<b) {
                        a = (int) Math.round(Math.random() * 100);
                        b = (int) Math.round(Math.random() * 100);
                    }
                    int c3 = in.nextInt();
                    output.println(a+"-"+b+"="+c3);
                    if (c3 == js.jian(a,b)) {
                        sum += 10;
                        System.out.println("答案正确");
                    }
                    else {
                        System.out.println("答案错误");
                    }
                    break ;

                    } 

               }
             System.out.println("成绩"+sum);
             output.println("成绩:"+sum);
             output.close();
         }
     }

 package shiyan;

 public class jisuanji<T> {
     private T a;
     private T b;
     public jisuanji() {
         a=null;
         b=null;
     }
     public jisuanji(T a,T b) {
         this.a=a;
         this.b=b;
     }
     public int jia(int a,int b)
     {
         return a+b;
     }
     public int jian(int a,int b)
     {
         return a-b;
     }
     public int chen(int a,int b)
     {
         return a*b;
     }
     public int chu(int a,int b)
     {
         if(b!=0&&a%b==0)
             return a/b;
         else
             return 0;
     }
 }

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。