徐思201771010132《面向对象程序设计（java）》第十周学习总结

Posted 2021-01-17 sisi-713

一、理论知识部分

泛型：也称参数化类型，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）

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。

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。

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

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。

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。

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。一个类型变量或通配符可以有多个限定，限定类型用“&”分割。

泛型变量下界: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。

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> 
{
   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
{
   public static void main(String[] args)
   {
      String[] words = { "Mary", "had", "a", "little", "lamb" };//泛型对象是字符串对象
      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)//用具体的类型替换类型变量可以实例化泛型类型
   {
      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;

/**
 * @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.LocalDate;

/**
 * @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) //通过对类型变量T设置限定，将T限制为实现了Comparable接口的类
   {
      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);
   }
}

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 1.00 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);      
      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());
   }
//打印雇员对的方法
   public static void printBuddies(Pair<? extends Employee> p)//使用通配符类型，表示带有上界。
   {
      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)//表示带有下界。
   {
      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)//无限定的通配符
   {
      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：主类Main   子类Person

模块说明：Main：查找文件，对文件进行读取。

Person：对文件进行具体的处理

package ID;

public class Person implements Comparable<Person> {
    private String name;
    private String ID;
    private int age;
    private String sex;
    private String birthplace;

    public String getname() {
        return name;
    }

    public void setname(String name) {
        this.name = name;
    }

    public String getID() {
        return ID;
    }

    public void setID(String ID) {
        this.ID = ID;
    }

    public int getage() {

        return age;
    }

    public void setage(int age) {

        this.age = age;
    }

    public String getsex() {
        return sex;
    }

    public void setsex(String sex) {
        this.sex = sex;
    }

    public String getbirthplace() {
        return birthplace;
    }

    public void setbirthplace(String birthplace) {
        this.birthplace = birthplace;
    }

    public int compareTo(Person o) {
        return this.name.compareTo(o.getname());
    }

    public String toString() {
        return name + "	" + sex + "	" + age + "	" + ID + "	" + birthplace + "
";
    }
}

package ID;

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<Person> Personlist;

    public static void main(String[] args) {
        Personlist = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        File file = new File("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 ID = linescanner.next();
                String sex = linescanner.next();
                String age = linescanner.next();
                String place = linescanner.nextLine();
                Person Person = new Person();
                Person.setname(name);
                Person.setID(ID);
                Person.setsex(sex);
                int a = Integer.parseInt(age);
                Person.setage(a);
                Person.setbirthplace(place);
                Personlist.add(Person);

            }
        } catch (FileNotFoundException e) {
            System.out.println("查找不到信息");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("信息读取有误");
            e.printStackTrace();
        }
        boolean isTrue = true;
        while (isTrue) {
            System.out.println("1:按姓名字典序输出人员信息");
            System.out.println("2:查询最大年龄与最小年龄人员信息");
            System.out.println("3：按省份找同乡");
            System.out.println("4:输入你的年龄,查询年龄与你最近人的信息");
            System.out.println("5：退出");
            int nextInt = scanner.nextInt();
            switch (nextInt) {
            case 1:
                Collections.sort(Personlist);
                System.out.println(Personlist.toString());
                break;
            case 2:
                int max = 0, min = 100;
                int j, k1 = 0, k2 = 0;
                for (int i = 1; i < Personlist.size(); i++) {
                    j = Personlist.get(i).getage();
                    if (j > max) {
                        max = j;
                        k1 = i;
                    }
                    if (j < min) {
                        min = j;
                        k2 = i;
                    }

                }
                System.out.println("年龄最大：" + Personlist.get(k1));
                System.out.println("年龄最小：" + Personlist.get(k2));
                break;
            case 3:
                System.out.println("省份?");
                String find = scanner.next();
                String place = find.substring(0, 3);
                String place2 = find.substring(0, 3);
                for (int i = 0; i < Personlist.size(); i++) {
                    if (Personlist.get(i).getbirthplace().substring(1, 4).equals(place))
                        System.out.println("同乡 " + Personlist.get(i));

                }

                break;
            case 4:
                System.out.println("年龄：");
                int yourage = scanner.nextInt();
                int near = agenear(yourage);
                int d_value = yourage - Personlist.get(near).getage();
                System.out.println("" + Personlist.get(near));

                break;
            case 5:
                isTrue = false;
                System.out.println("欢迎使用!");
                break;
            default:
                System.out.println("输入有误");
            }
        }
    }

    public static int agenear(int age) {

        int j = 0, min = 53, d_value = 0, k = 0;
        for (int i = 0; i < Personlist.size(); i++) {
            d_value = Personlist.get(i).getage() - age;
            if (d_value < 0)
                d_value = -d_value;
            if (d_value < min) {
                min = d_value;
                k = i;
            }
        }
        return k;
    }
}

问题：查找不到文件，代码编程不是太会

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：主类：Main   子类：math

模块说明：Main：随机生成十道100内的计算题，并判断答案正误

math：对具体计算进行处理

public class math {
    private int a;
    private int b;

    public static int add(int a, int b) {
        return a + b;
    }

    public static int reduce(int a, int b) {
        return a - b;
    }

    public static int multiplication(int a, int b) {
        return a * b;
    }

    public static int division(int a, int b) {
        if (b != 0)
            return a / b;
        else
            return 0;
    }
}

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

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

        Scanner in = new Scanner(System.in);

        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() * 4);
            switch (m) {
            case 1:
                System.out.println(i + ": " + a + "/" + b + "=");
                while (b == 0) {
                    b = (int) Math.round(Math.random() * 100);
                }
                int c1 = in.nextInt();
                if (c1 == a / b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }

                break;

            case 2:
                System.out.println(i + ": " + a + "*" + b + "=");
                int c2 = in.nextInt();
                if (c2 == a * b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }
                break;
            case 3:
                System.out.println(i + ": " + a + "+" + b + "=");
                int c3 = in.nextInt();
                if (c3 == a + b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }

                break;
            case 4:
                System.out.println(i + ": " + a + "-" + b + "=");
                int c4 = in.nextInt();
                if (c4 == a - b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }
                break;

            }

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

问题：不符合小学四则运算要求，有的计算结果出现了负数

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。

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

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

        Scanner in = new Scanner(System.in);

        PrintWriter output = null;
        try {
            output = 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() * 4);
            switch (m) {
            case 1:
                while (b == 0) {
                    b = (int) Math.round(Math.random() * 100);
                }
                while (a % b != 0) {
                    a = (int) Math.round(Math.random() * 100);
                }
                System.out.println(i + ": " + a + "/" + b + "=");
                int c1 = in.nextInt();
                output.println(a + "/" + b + "=" + c1);
                if (c1 == a / b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }

                break;

            case 2:
                System.out.println(i + ": " + a + "*" + b + "=");
                int c2 = in.nextInt();
                output.println(a + "*" + b + "=" + c2);
                if (c2 == a * b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }
                break;
            case 3:
                System.out.println(i + ": " + a + "+" + b + "=");
                int c3 = in.nextInt();
                output.println(a + "+" + b + "=" + c3);
                if (c3 == a + b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }

                break;
            case 4:
                while (a < b) {
                    a = (int) Math.round(Math.random() * 100);
                }
                System.out.println(i + ": " + a + "-" + b + "=");
                int c4 = in.nextInt();
                output.println(a + "-" + b + "=" + c4);
                if (c4 == a - b) {
                    System.out.println("恭喜答案正确");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案错误");
                }
                break;

            }

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

public class math<T> {
    private T a;
    private T 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 && a % b == 0)
            return a / b;
        else
            return 0;
    }
}

三：实验总结:

 通过这次实验，我了解了泛型类，泛型方法、通配符、泛型变量上界、泛型变量下界。通过对之前实验的总结，对之前的知识进行进一步的回顾，通过改进代码更好的了解了泛型程序设计。编程仍需多加练习，对之前的知识需要多加复习巩固。