马凯军201771010116《面向对象与程序设计Java》第十周学习总结

一、理论知识学习部分

泛型类的约束与局限性：

不能用基本类型实例化类型参数
 运行时类型查询只适用于原始类型
 不能抛出也不能捕获泛型类实例
 参数化类型的数组不合法
 不能实例化类型变量
 泛型类的静态上下文中类型变量无效
 注意擦除后的冲突

Java 中泛型类不具协变性。如果能够将List<Integer>赋给List<Number>。那么下面的代码就允许将非Integer的内容放入List<Integer>：
List<Integer> li = new ArrayList<Integer>();
List<Number> ln = li; // illegal
ln.add(new Float(3.1415));
 泛型类可扩展或实现其它的泛型类。例如，
ArrayList<T>类实现List<T>接口。这意味着，一个ArrayList<Manager> 可以被转换为一个List<Manager>。

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。

定义一个泛型类时，在“＜＞”内定义形式类型参数，例如：“class TestGeneric＜K, V＞”，其中“K” , “V”不代表值，而是表示类型。
 实例化泛型对象的时候，一定要在类名后面指定类型参数的值（类型），一共要有两次书写。例如：
TestGeneric＜String, String＞ t
=new TestGeneric＜String, String＞()；
 泛型中＜T extends Object＞, extends并不代表继承，它是类型范围限制。
 泛型类不是协变的。

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：

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> //引入类型变量T
{
   private T first;//运用类型变量T
   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 = { "ary", "had", "a", "little", "lamb" };//定义多个字符串
      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)//调用静态minmax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];//compareTo方法比较两个字符串
         if (max.compareTo(a[i]) < 0) max = a[i];
      }
      return new Pair<>(min, max);//用一个Pair对象返回两个结果
   }
}

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(1907, 12, 9), // G. Hopper
            LocalDate.of(1834, 12, 10), // A. Lovelace
            LocalDate.of(1923, 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)// 对类型变量T进行限定，将T限制为实现了Comparable接口的类：<T extends Comparable>。
   {
      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;

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))//?是通配符，表明参数的类型是上界为Employee的任何一种类型
   {
      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))//?是通配符，表明参数的类型是下界为manager的任何一种类型
   {
      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)//?是通配符，表明参数的类型是下界为manager的任何一种类型
   {
      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）。

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）。

程序总体结构：主类Test和Citizen类

模块说明：

主类Test：文件的读取，根据实验要求编辑相关代码。

Citizen类：对所需数据进行具体的处理。

存在的问题：文件读入时在文件的读取方面存在一定的问题，在数据处理方面的转换也有相应的问题。

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.Scanner;
import java.util.Collections;//对集合进行排序、查找、修改等；

public class Test {
    private static ArrayList<Citizen> citizenlist;

    public static void main(String[] args) {
        citizenlist = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        //读文件
        File file = new File("E:/java/身份证号.txt");
        //异常捕获
        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 birthplace = linescanner.nextLine();
                Citizen citizen = new Citizen();
                citizen.setName(name);
                citizen.setId(id);
                citizen.setSex(sex);
                // 将字符串转换成10进制数
                int ag = Integer.parseInt(age);
                citizen.setage(ag);
                citizen.setBirthplace(birthplace);
                citizenlist.add(citizen);

            }
        } catch (FileNotFoundException e) {
            System.out.println("信息文件找不到");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("信息文件读取错误");
            e.printStackTrace();
        }
        boolean isTrue = true;
        //根据题目要求编写相关代码
        while (isTrue) {

            System.out.println("1.按姓名字典序输出人员信息");
            System.out.println("2.查询最大年龄的人员信息、查询最小年龄人员信息");
            System.out.println("3.查询人员中是否查询人员中是否有你的同乡");
            System.out.println("4.输入你的年龄，查询文件中年龄与你最近人的姓名、身份证号、年龄、性别和出生地");
            System.out.println("5.退出");
            int nextInt = scanner.nextInt();
            switch (nextInt) {
            case 1:
                Collections.sort(citizenlist);
                System.out.println(citizenlist.toString());
                break;
            case 2:
                int max = 0, min = 100;
                int m, k1 = 0, k2 = 0;
                for (int i = 1; i < citizenlist.size(); i++) {
                    m = citizenlist.get(i).getage();
                    if (m > max) {
                        max = m;
                        k1 = i;
                    }
                    if (m < min) {
                        min = m;
                        k2 = i;
                    }
                }
                System.out.println("年龄最大：" + citizenlist.get(k1));
                System.out.println("年龄最小：" + citizenlist.get(k2));
                break;
            case 3:
                System.out.println("出生地：");
                String find = scanner.next();
                String place = find.substring(0, 3);
                for (int i = 0; i < citizenlist.size(); i++) {
                    if (citizenlist.get(i).getBirthplace().substring(1, 4).equals(place))
                        System.out.println("出生地" + citizenlist.get(i));
                }
                break;
            case 4:
                System.out.println("年龄：");
                int yourage = scanner.nextInt();
                int near = peer(yourage);
                int j = yourage - citizenlist.get(near).getage();
                System.out.println("" + citizenlist.get(near));
                break;
            case 5:
                isTrue = false;
                System.out.println("程序已退出!");
                break;
            default:
                System.out.println("输入有误");
            }
        }
    }

    public static int peer(int age) {
        int flag = 0;
        int min = 53, j = 0;
        for (int i = 0; i < citizenlist.size(); i++) {
            j = citizenlist.get(i).getage() - age;
            if (j < 0)
                j = -j;
            if (j < min) {
                min = j;
                flag = i;
            }
        }
        return flag;
    }
}

public class Citizen implements Comparable<Citizen> {

    private String name;
    private String id;
    private String sex;
    private int age;
    private String birthplace;
//对数据进行相关处理
    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 String getSex() {
        return sex;
    }

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

    public int getage() {
        return age;
    }

    public void setage(int age) {
        this.age = age;
    }

    public String getBirthplace() {
        return birthplace;
    }

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

    public int compareTo(Citizen other) {
        return this.name.compareTo(other.getName());
    }

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

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）。

程序总体结构：主类Calculator

模块说明：文件输出、生成四则运算计算器。

存在的问题：不能将输出结果生成相应的文件。

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

public class calculator {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        PrintWriter out = null;
        try {
            //文件输出
            out = new PrintWriter("test.txt");
            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 menu = (int) Math.round(Math.random() * 3);
                //随机生成四则运算
                switch (menu) {
                case 0:
                    System.out.println(i+":"+a + "+" + b + "=");
                    int c1 = in.nextInt();
                    out.println(a + "+" + b + "=" + c1);
                    if (c1 == (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) {
                        b = (int) Math.round(Math.random() * 100);
                    }
                    System.out.println(i+":"+a + "-" + b + "=");
                    int c2 = in.nextInt();
                    out.println(a + "-" + b + "=" + c2);
                    if (c2 == (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 c3 = in.nextInt();
                    out.println(a + "*" + b + "=" + c3);
                    if (c3 == 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){
                            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 c4 = in.nextInt();
                    if (c4 == 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);
            out.println("你的得分为" + sum);
            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

}

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

public class calculator {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Count count=new Count();
        PrintWriter out = null;
        try {
            out = new PrintWriter("test.txt");
            int sum = ;
            for (int i = ; i <=; i++) {
                int a = (int) Math.round(Math.random() * );
                int b = (int) Math.round(Math.random() * );
                int menu = (int) Math.round(Math.random() * );
                switch (menu) {
                case :
                    System.out.println(i+":"+a + "+" + b + "=");
                    int c1 = in.nextInt();
                    out.println(a + "+" + b + "=" + c1);
                    if (c1 == (a + b)) {
                        sum += ;
                        System.out.println("恭喜答案正确");
                    } else {
                        System.out.println("抱歉，答案错误");
                    }
                    break;
                case :
                    while (a < b) {
                        b = (int) Math.round(Math.random() * );
                    }
                    System.out.println(i+":"+a + "-" + b + "=");
                    int c2 = in.nextInt();
                    out.println(a + "-" + b + "=" + c2);
                    if (c2 == (a - b)) {
                        sum += ;
                        System.out.println("恭喜答案正确");
                    } else {
                        System.out.println("抱歉，答案错误");
                    }

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

                    break;
                case :
                     while(b == ){
                            b = (int) Math.round(Math.random() * );
                        }
                        while(a % b != ){
                            a = (int) Math.round(Math.random() * );

                        }
                    System.out.println(i+":"+a + "/" + b + "=");
                    int c4 = in.nextInt();
                    if (c4 == a / b) {
                        sum += ;
                        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);
            out.println("你的得分为" + sum);
            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

}

public class Count<T> {
    private T a;
    private T b;
    public Count() {
        a=null;
        b=null;
    }
    public Count(T a,T b) {
        this.a=a;
        this.b=b;
    }
    public int count1(int a,int b) {
        return a+b;
    }
    public int count2(int a,int b) {
        return a-b;
    }
    public int count3(int a,int b) {
        return a*b;
    }
    public int count4(int a,int b) {
        return a/b;
    }

实验总结：

理解掌握了泛型类的定义与使用，泛型方法的声明与使用；泛型接口的定义与实现；此外，对上次实验的总结反思方面，从中发现了一些问题，尤其是四则运算的编程，相比上次实验，从中认识到了很多不足，也在程序结果的导成相应文件方面也有很大的问题，希望在这周的学习中通过老师的指导将这方面在提升一下。在这次实验的过程中最大的收获就是通过刚学习的泛型类，能使四则运算的编程更加的全面，可以实现各种数据类型的运算。有了很大的提升。