201771010106东文财《面向对象程序设计（java）》实验10

实验十  泛型程序设计技术

实验时间 2018-11-4

一、理论知识

1、JDK 5.0 中增加的泛型类型，是Java 语言中类型安全的一次重要改进。

2、 泛型：也称参数化类型(parameterized type)，就是在定义类、接口和方法时，通过类型参数指示将要处理的对象类型。（如ArrayList类）

3、泛型程序设计（Generic programming）：编写代码可以被很多不同类型的对象所重用。

4、一个泛型类（generic class）就是具有一个或多个类型变量的类，即创建用类型作为参数的类。如一个泛型类定义格式如下：class Generics＜K,V＞其中的K和V是类中的可变类型参数。

5、Pair类引入了一个类型变量T，用尖括号（<>）括起来，并放在类名的后面。

6、 泛型类可以有多个类型变量。例如:public class Pair<T, U> { … }

7、 类定义中的类型变量用于指定方法的返回类型以及域、局部变量的类型。

8、 泛型方法

（1） 除了泛型类外，还可以只单独定义一个方法作为泛型方法，用于指定方法参数或者返回值为泛型类型，留待方法调用时确定。

（2） 泛型方法可以声明在泛型类中，也可以声明在普通类中。

二、实验部分

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> //定义公共类，Pair类引入了一个类型变量T，用于指定方法的返回类型以及域、局部变量的类型。
{
   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 pair1;

/**
 * @version 1.01 2012-01-26
 * @author Cay Horstmann
 */
public class PairTest1//定义公共类
{
   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//另一个类
{
   /**
    * 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)
   {
      if (a == null || a.length == 0) return null;//条件判断语句
      String min = a[0];
      String max = a[0];
      for (int i = 1; i < a.length; i++)//for循环语句
      {
         if (min.compareTo(a[i]) > 0) min = a[i];
         if (max.compareTo(a[i]) < 0) max = a[i];
      }
      return new Pair<>(min, max);
   }
}

实验结果：

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;

/**
 * @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 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);
   }
}

实验结果：

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;

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;
   }
}

 

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;

/**
 * @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);
   }
}

实验结果：

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）。

 总体结构：

类people

1、读入文件等

2、定义了查找人员信息的方法

3、分5个case来分别说年龄大小、等。

出现问题：

过程中出现了很多问题，主要原因还是在于自己的粗心和对一些知识的掌握不够，不过在和同学们的交流和学习中得以解决，以后我会接续努力的。

package gh;
    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.Scanner;
    import java.util.Collections;

    public class tt {

        public static People findPeopleByname(String name) {
            People flag = null;
            for (People people : peoplelist) {
                if(people.getName().equals(name)) {
                    flag = people;
                }
            }
            return flag;

        }

        public static People findPeopleByid(String id) {
            People flag = null;
            for (People people : peoplelist) {
                if(people.getnumber().equals(id)) {
                    flag = people;
                }
            }
            return flag;

        }
         
        private static ArrayList<People> agenear(int yourage) {
            // TODO Auto-generated method stub
            int j=0,min=53,d_value=0,k = 0;
            ArrayList<People> plist = new ArrayList<People>();
            for (int i = 0; i < peoplelist.size(); i++) {
                d_value = peoplelist.get(i).getage() > yourage ? 
                        peoplelist.get(i).getage() - yourage : yourage - peoplelist.get(i).getage() ;
                k = d_value < min ? i : k;
                min = d_value < min ? d_value : min;
            }
            for(People people : peoplelist) {
                if(people.getage() == peoplelist.get(k).getage()) {
                    plist.add(people);
                }
            }
            return plist;
        }

        private static ArrayList<People> peoplelist; 
        
        public static void main(String[] args) //throws  IOException
        {
            peoplelist = new ArrayList<People>();
            Scanner scanner = new Scanner(System.in);
            File file = new File("D:\\身份证号.txt");
            try {
                FileInputStream files = new FileInputStream(file);
                BufferedReader in = new BufferedReader(new InputStreamReader(files));
                String temp = null;
                while ((temp = in.readLine()) != null) {
                    
                    String[] information = temp.split("[ ]+");
                    People people = new People();
                    people.setName(information[0]);
                    people.setnumber(information[1]);
                    int A = Integer.parseInt(information[3]);
                    people.setage(A);
                    people.setsex(information[2]);
                    for(int j = 4; j<information.length;j++) {
                        people.setplace(information[j]);
                    }
                    peoplelist.add(people);

                }
            } catch (FileNotFoundException e) {
                System.out.println("文件未找到");
                e.printStackTrace();
            } catch (IOException e) {
                System.out.println("文件读取错误");
                e.printStackTrace();
            }
            boolean isTrue = true;
            while (isTrue) {

                System.out.println("******************************************");
                System.out.println("   1.按姓名典序输出人员信息");
                System.out.println("   2.查询最大年龄人员信息");
                System.out.println("   3.查询最小年龄人员信息");
                System.out.println("   4.输入你的年龄，查询身份证号.txt中年龄与你最近的人");
                System.out.println("   5.查询人员中是否有你的同乡");
                System.out.println("   6.退出");
                System.out.println("******************************************");
                int nextInt = scanner.nextInt();
                switch (nextInt) {
                case 1:
                    Collections.sort(peoplelist);
                    System.out.println(peoplelist.toString());
                    break;
                case 2:
                    int max=0;
                    int j,k1 = 0;
                    for(int i=1;i<peoplelist.size();i++)
                    {
                        j = peoplelist.get(i).getage();
                       if(j>max)
                       {
                           max = j; 
                           k1 = i;
                       }
                      
                    }  
                    System.out.println("年龄最大："+peoplelist.get(k1));
                    break;
                case 3:
                    int min = 100;
                    int j1,k2 = 0;
                    for(int i=1;i<peoplelist.size();i++)
                    {
                        j1 = peoplelist.get(i).getage();
                        if(j1<min)
                        {
                            min = j1; 
                            k2 = i;
                        }

                     } 
                    System.out.println("年龄最小："+peoplelist.get(k2));
                    break;
                case 4:
                    System.out.println("年龄：");
                    int input_age = scanner.nextInt();
                    ArrayList<People> plist = new ArrayList<People>();
                    plist = agenear(input_age);
                    for(People people : plist) {
                        System.out.println(people.toString());
                    }
                    break;
                case 5:
                    System.out.println("请输入省份");
                    String find = scanner.next();        
                    for (int i = 0; i <peoplelist.size(); i++) 
                    {
                        String [] place = peoplelist.get(i).getplace().split("\t");
                        for(String temp : place) {
                            if(find.equals(temp)) {
                                System.out.println("你的同乡是    "+peoplelist.get(i));
                                break;
                            }
                        }
                        
                    } 
                    break;
                case 6:
                    isTrue = false;
                    System.out.println("byebye!");
                    break;
                default:
                    System.out.println("输入有误");
                }
            }
        }

    }
}

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）。

 

总体结构：

类main

1、程序中的文件读取等

出现问题：

1.没有定义文件输出的路径，找输出文件不简单。

解决方法：只需定义路径即可如：

("E:\\壁纸\\海贼王\\text.txt");

 

 

package rt;


    import java.io.FileNotFoundException;
    import java.io.PrintWriter;
    import java.util.Scanner;
    public class tt {
        public static void main(String[] args) {
            Scanner in = new Scanner(System.in);
            tt1 computing=new tt1();
            PrintWriter output = null;
            try {
                output = new PrintWriter("tt.txt");
            } catch (Exception e) {
            }
            int sum = 0;

            for (int i = 1; i < 11; i++) {
                int a = (int) Math.round(Math.random() * 100);
                int b = (int) Math.round(Math.random() * 100);
                int s = (int) Math.round(Math.random() * 3);
            switch(s)
            {
               case 1:
                   System.out.println(i+": "+a+"/"+b+"=");
                   while(b==0){  
                       b = (int) Math.round(Math.random() * 100); 
                       }
                   double c = in.nextDouble();
                   output.println(a+"/"+b+"="+c);
                   if (c == (double)computing.division(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   }
                   else {
                       System.out.println("错误");
                   }
                
                   break;
                
               case 2:
                   System.out.println(i+": "+a+"*"+b+"=");
                   int c1 = in.nextInt();
                   output.println(a+"*"+b+"="+c1);
                   if (c1 == computing.multiplication(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   }
                   else {
                       System.out.println("错误");
                   }
                   break;
               case 3:
                   System.out.println(i+": "+a+"+"+b+"=");
                   int c2 = in.nextInt();
                   output.println(a+"+"+b+"="+c2);
                   if (c2 == computing.addition(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   }
                   else {
                       System.out.println("错误");
                   }
                   
                   break ;
               case 4:
                   System.out.println(i+": "+a+"-"+b+"=");
                   int c3 = in.nextInt();
                   output.println(a+"-"+b+"="+c3);
                   if (c3 == computing.subtraction(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   }
                   else {
                       System.out.println("错误");
                   }
                   break ;

                   } 
        
              }
            System.out.println("成绩："+sum+"分");
            output.println("成绩："+sum+"分");
            output.close();
             
        }
    }
    class tt1
    {
           private int a;
           private int b;
            public int  addition(int a,int b)
            {
                return a+b;
            }
            public int  subtraction(int a,int b)
            {
                if((a-b)<0)
                    return 0;
                else
                return a-b;
            }
            public int   multiplication(int a,int b)
            {
                return a*b;
            }
            public int   division(int a,int b)
            {
                if(b!=0)
                return a/b;    
                else
            return 0;
            }

            
    }

 

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 hh;

public class jj<T> {
private T a;
private T b;
public jj() {
a = null;
b = null;
}

public jj(T a, T b) {
this.a = a;
this.b = b;
}
public int jj1(int a,int b)
{
return a+b;
}
public int jj2(int a,int b)
{
return a-b;
}
public int jj3(int a,int b)
{
return a*b;
}
public int jj4(int a,int b)
{
if(b!=0)
return a/b;
else return 0;
}

}

 

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


    public class kk {
        public static void main(String[] args) {

            Scanner in = new Scanner(System.in);
            jj counter=new jj();
            PrintWriter out = null;
            try {
                out = new PrintWriter("E:\\壁纸\\海贼王\\text.txt");
            } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            int sum = 0;

            
            
            for (int i = 0; i <10; i++) {
                int a = (int) Math.round(Math.random() * 100);
                int b = (int) Math.round(Math.random() * 100);
                int m= (int) Math.round(Math.random() * 3);

                
               switch(m)
               {
               case 0:
                   System.out.println(a + "+" + b + "=");
                   int d0 = in.nextInt();
                   out.println(a + "+" + b + "=" + d0);
                   if (d0 == counter.jj1(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   } else {
                       System.out.println("错误");
                   }
                   break;
               case 1:
                   while (a < b) {
                       int x = a;
                       a = b;
                       b = x;
                   }
                   System.out.println(a + "-" + b + "=");
                   int c1 = in.nextInt();
                   out.println(a + "-" + b + "=" + c1);
                   if (c1 == counter.jj2(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   } else {
                       System.out.println("错误");
                   }
                   break;
               case 2:
                   System.out.println(a + "*" + b + "=");
                   int c2 = in.nextInt();
                   out.println(a + "*" + b + "=" + c2);
                   if (c2 ==counter.jj3(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   } else {
                       System.out.println("错误");
                   }
                   break;
               case 3:
                   while (b == 0 || a % b != 0) {
                       a = (int) Math.round(Math.random() * 100);
                       b = (int) Math.round(Math.random() * 100);
                   }
                   System.out.println(a + "/" + b + "=");
                   int c3 = in.nextInt();
                   out.println(a + "/" + b + "=" + c3);
                   if (c3 == counter.jj4(a, b)) {
                       sum += 10;
                       System.out.println("正确");
                   } else {
                       System.out.println("错误");
                   }
                   break;

               }

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

             
        }
        }

实验结果：

实验总结：

   本章我们主要学习了泛型程序设计，使用泛型机制编写的程序代码要比那些杂乱地使用Object变量，然后再进行强行类型转换的代码具有更好的安全性和可读性。反省对于集合类尤其有用。通过课后一些简单程序的编译，运行，知道了如何定义简单的泛型类，和他的一些用法。希望在以后的编程中我会多多的用到这些学过的知识。