201771010112罗松《面向对象程序设计（java）》第十周学习总结

Posted 2021-01-17 xuezhiqian

 

 

                                                                                                                                                                                                                     实验十  泛型程序设计技术

                                                                                                                                                                                                                          实验时间 2018-11-4

 

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。 

代码：

package pair1;

/**
 * @version 1.00 2004-05-10
 * @author Cay Horstmann
 */
//泛型类使得类具有通用性
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 pair1;

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);//泛型类对象String Pair类，静态方法用类名调用方法,泛型字符串类型，按字典序排序
      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)//普通方法，返回值是一个实例化的Pair类对象
   {
      if (a == null || a.length == 0) return null;//length是数组的属性值
      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);//用泛型类来返回两个值
   }
}

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。

代码：

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) //泛型方法，有上界约束
   {
      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);
   }
}

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。

代码：

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;
   }
}

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);  //类型变量    
      printBuddies(buddies);

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

      Pair<Employee> result = new Pair<>();//也可以用Manager
      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)//上界约束
   {
      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)//采用通配符来定义第二个类型变量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)//？类型变量的通配符，单独的？表示任何一种类型，T表示一种未知类型
   //将hasNulls转换成泛型方法
   //测试一个pair是否包含一个null引用
   {
      return p.getFirst() == null || p.getSecond() == null;
   }
//编写一个交换成对元素的方法
   public static void swap(Pair<?> p) { swapHelper(p); }

   public static <T> void swapHelper(Pair<T> p)//泛型方法
   {
      T t = p.getFirst();//保存第一个元素
      p.setFirst(p.getSecond());
      p.setSecond(t);
   }
}

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）。

总体结构说明：

主类main，子类card

模块说明：

main

package shen;

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 {
    /**
     * 1.文件读取模块 利用ArrayList构造studentlist存放文件内容2. 创建文件字符流，分类读取文件内容 3.try/catch语句捕获异常
     */
    private static ArrayList<Student> studentlist;

    public static void main(String[] args) {
        studentlist = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        File file = new File("C:\\Users\\ASUS\\Desktop\\新建文件夹\\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();
            // 加入的捕获异常代码
        } catch (IOException e) {
            System.out.println("学生信息文件读取错误");
            e.printStackTrace();
            // 加入的捕获异常代码
        }
        /*
         * 1.根据实验要求，选择具体操作的模块 2.利用switch语句选择具体的操作
         */
        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("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");

            }
        }
    }

    /*
     * 对年龄数据进行相应的处理
     */
    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

card：

package shen;

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 {
    /**
     * 1.文件读取模块 利用ArrayList构造studentlist存放文件内容2. 创建文件字符流，分类读取文件内容 3.try/catch语句捕获异常
     */
    private static ArrayList<Student> studentlist;

    public static void main(String[] args) {
        studentlist = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        File file = new File("C:\\Users\\ASUS\\Desktop\\新建文件夹\\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();
            // 加入的捕获异常代码
        } catch (IOException e) {
            System.out.println("学生信息文件读取错误");
            e.printStackTrace();
            // 加入的捕获异常代码
        }
        /*
         * 1.根据实验要求，选择具体操作的模块 2.利用switch语句选择具体的操作
         */
        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("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");

            }
        }
    }

    /*
     * 对年龄数据进行相应的处理
     */
    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

问题：目前程序设计存在的困难与问题：读文件时，文件路径不正确，无法找到文件。

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）。

总体结构说明：

主类test和子类yunsuan

模块说明：

package demo;

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

public class Test {
    public static void main(String[] args) {
        //文件输出模块，调用构造函数

        @SuppressWarnings("resource")
        Scanner in = new Scanner(System.in);
        Demo demo=new Demo();
        //创建文件字符流，将output中的内容设为空（null）
        PrintWriter output = null;
        try {
            output = new PrintWriter("test.txt");//将out结果输出到test.txt中
        } catch (Exception e) {
            e.printStackTrace();
        }
        int sum = 0; //定义一个sum，计算成绩
        
        //四则运算生成模块，生成10道题目
        for (int i = 0; i < 10; i++) {

            int a = (int) Math.round(Math.random() * 100);
            int b = (int) Math.round(Math.random() * 100);
            int c = (int) Math.round(Math.random() * 3);
            switch (c) {
            case 0:
                System.out.println(a + "+" + b + "=");
                int d0 = in.nextInt();
                output.println(a + "+" + b + "=" + d0);
                if (d0 == demo.demo1(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();
                output.println(a + "-" + b + "=" + d1);
                if (d1 == demo.demo2(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();
                output.println(a + "*" + b + "=" + d2);
                if (d2 == demo.demo3(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();
                output.println(a + "/" + b + "=" + d3);
                if (d3 == demo.demo4(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("你的得分为" + sum);
        output.println("你的得分为" + sum); //将循环结果输出到test.txt中
        output.close();
    }
}

Test

package demo;

public class yunsuan {
       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;            
        }

}

yunsuan

问题：对printwrite不太了解。

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。

代码：

package demo;

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

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

        @SuppressWarnings("resource")
        Scanner in = new Scanner(System.in);
        Demo demo=new Demo();

        PrintWriter output = null;
        try {
            output = new PrintWriter("test.txt");
        } catch (Exception e) {
            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 c = (int) Math.round(Math.random() * 3);
            switch (c) {
            case 0:
                System.out.println(a + "+" + b + "=");
                int d0 = in.nextInt();
                output.println(a + "+" + b + "=" + d0);
                if (d0 == demo.demo1(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();
                output.println(a + "-" + b + "=" + d1);
                if (d1 == demo.demo2(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();
                output.println(a + "*" + b + "=" + d2);
                if (d2 == demo.demo3(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();
                output.println(a + "/" + b + "=" + d3);
                if (d3 == demo.demo4(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("你的得分为" + sum);
        output.println("你的得分为" + sum);
        output.close();
    }
}

Test

package demo;

public class yunsuan {
       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;            
        }

}

yunsuan

结果：

实验总结：通过这周的学习，我了解了泛型设计技术的概念，以及它的好处和限制，基本上会运用泛型技术设计程序，但是在很多知识的运用方面仍然不太懂，在之后的学习中要更加努力，课后要多练习，也希望老师能更加详细的讲解。