实验十 泛型程序设计技术

实验十  泛型程序设计技术

实验时间 2018-11-1

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：

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；

在泛型类定义及使用代码处添加注释；

掌握泛型类的定义及使用。

程序源代码及其注释：

Pair.java

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; }
}

PairTest1.java

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);
   }
}

程序测试结果如下所示：

测试程序2：

编辑、调试运行教材315页 PairTest2，结合程序运行结果理解程序；

在泛型程序设计代码处添加相关注释；

掌握泛型方法、泛型变量限定的定义及用途。

程序源代码及其注释：

Pair.java

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; }
}

PairTest2.java:

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);
   }
}

程序测试结果如下所示：

测试程序3：

用调试运行教材335页 PairTest3，结合程序运行结果理解程序；

了解通配符类型的定义及用途。

程序的源代码及其注释；
PairTest3.java:

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)
  //? extends type，表示带有上界 

   {
      Employee first = p.getFirst();
      Employee second = p.getSecond();
      System.out.println(first.getName() + " and " + second.getName() + " are buddies.");
   }
 //"?"在这儿是通配符，符号表明参数的类型可以是任何一种类型，它和参数T的含义是有区别的
   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);
   }
//T表示一种未知类型，而“？”表示任何一种类型
   public static void maxminBonus(Manager[] a, Pair<? super Manager> result)
   {
      minmaxBonus(a, result);
      PairAlg.swapHelper(result); // swapHelper捕获通配符类型
   }
   // 不能写公共静态<T超级管理器> ...
}

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);
   }
}

Employee.java

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;
   }
}

Manager.java

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;
   }
}

Pair.java

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; }
}

程序测试结果如下所示；

实验2：编程练习：

编程练习1：实验九编程题总结

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）。

程序总体结构：

主要的两个大类，有主类Main和子类Student

模块说明

在这一模块中主要讲txt文件导入到程序，

分别用5个小类case来定义程序索要查找的同乡，年龄相近的人等等

Main

package Test;

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.Arrays;
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("D:\\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.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("e.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 "e":
                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;
      }

}

Main

Student

package Test;

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";
    }
}

Student

实验困惑：分不清在程序运行的过程中这个读取身份证的字节是怎么运行的，还有就是这个程序读取的txt文件的内容不同的名字的字节不会调

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）。

程序总体结构

实验程序主要有两个大类，Demo类和suanfa类

模块说明

在设计四则运算的时候，首先判断代码的正确性，也就是异常处理

然后进行四则运算。判断代码的进一步完善

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

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

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

        for (int i = 1; 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(i+": "+a+"/"+b+"=");

               while(b==0){  b = (int) Math.round(Math.random() * 100); }

            int c0 = in.nextInt();
            out.println(a+"/"+b+"="+c0);
            if (c0 == counter.division(a, b)) {
                sum += 10;
                System.out.println("恭喜答案正确");
            }
            else {
                System.out.println("抱歉，答案错误");
            }

            break;

           case 1:
               System.out.println(i+": "+a+"*"+b+"=");
               int c = in.nextInt();
               out.println(a+"*"+b+"="+c);
               if (c == counter.multiplication(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               }
               else {
                   System.out.println("抱歉，答案错误");
               }
               break;
           case 2:
               System.out.println(i+": "+a+"+"+b+"=");
               int c1 = in.nextInt();
               out.println(a+"+"+b+"="+c1);
               if (c1 == counter.add(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               }
               else {
                   System.out.println("抱歉，答案错误");
               }

               break ;
           case 3:
               System.out.println(i+": "+a+"-"+b+"=");
               int c2 = in.nextInt();
               out.println(a+"-"+b+"="+c2);
               if (c2 == counter.reduce(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               }
               else {
                   System.out.println("抱歉，答案错误");
               }
               break ;

               } 

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

    }
    }

Demo

public class Suanfa {
   private int a;
   private int b;
    public int  add(int a,int b)
    {
        return a+b;
    }
    public int   reduce(int a,int b)
    {
        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;
    }

}

suanfa

实验的困惑：

对四测运算的处理还是不够精确，尤其是对于除法这一块

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。

程序源代码：

suanfa

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

   public Suanfa(T a, T b) {
       this.a = a;
       this.b = b;
   }
    public int   suanfa1(int a,int b)
    {
        return a+b;
    }
    public int   suanfa2(int a,int b)
    {
        return a-b;
    }
    public int   suanfa3(int a,int b)
    {
        return a*b;
    }
    public int   suanfa4(int a,int b)
    {
        if(b!=0)
        return a/b;
        else return 0;
    }

}

Demo:

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

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

        Scanner in = new Scanner(System.in);
        Suanfa counter=new Suanfa();
        PrintWriter out = null;
        try {
            out = new PrintWriter("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.suanfa1(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               } else {
                   System.out.println("抱歉，答案错误");
               }
               break;
           case 1:
               while (a < b) {
                   int x = a;
                   a = b;
                   b = x;
               }
               System.out.println(a + "-" + b + "=");
               int d1 = in.nextInt();
               out.println(a + "-" + b + "=" + d1);
               if (d1 == counter.suanfa2(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               } else {
                   System.out.println("抱歉，答案错误");
               }
               break;
           case 2:
               System.out.println(a + "*" + b + "=");
               int d2 = in.nextInt();
               out.println(a + "*" + b + "=" + d2);
               if (d2 ==counter.suanfa3(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               } else {
                   System.out.println("抱歉，答案错误");
               }
               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 d3 = in.nextInt();
               out.println(a + "/" + b + "=" + d3);
               if (d3 == counter.suanfa4(a, b)) {
                   sum += 10;
                   System.out.println("恭喜答案正确");
               } else {
                   System.out.println("抱歉，答案错误");
               }
               break;

           }

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

    }
    }

程序运行结果

实验总结

本章理论知识点总结

泛型：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

泛型程序设计：编写代码可以被很多不同类型的对象所重用。

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。

泛型类可以有多个类型变量。

泛型方法:

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。

泛型方法可以声明在泛型类中，也可以声明在普通类中。

泛型变量上界的说明

NumberGeneric类所能处理的泛型变量类型需和Number有继承关系；

extends关键字所声明的上界既可以是一个类，也可以是一个接口；

<T extends Bounding Type>表示T应该是绑定类型的子类型。

泛型变量下界的说明

通过使用super关键字可以固定泛型参数的类型为某种类型或者其超类

当程序希望为一个方法的参数限定类型时，通常可以使用下限通配符

通配符：

“？”符号表明参数的类型可以是任何一种类型，它和参数T的含义是有区别的。T表示一种未知类型，而“？”表示任何一种类型。这种通配符一般有以下三种用法：

单独的？，用于表示任何类型。

? extends type，表示带有上界。

? super type，表示带有下界。

通过本周的理论知识以及在实验课的学习，我基本掌握泛型程序设计的“泛型”到底指的是什么，我希望在以后的学习过程当中能够越来越好。

原文地址：https://www.cnblogs.com/791683057mxd/p/9890302.html