201771010118 马昕璐《面向对象程序设计java》第十周学习总结

第一部分：理论知识学习部分

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。

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。

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。

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

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。

– 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。

第二部分：实验部分

1.实验名称：实验十  泛型程序设计技术

2.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。

3.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> //Pair类引入一个变量
{
   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" };
      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)//返回值为实例化的类对象
   {
      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++)
      {
         if (min.compareTo(a[i]) > 0) min = a[i];
         if (max.compareTo(a[i]) < 0) max = a[i];
      }
      return new Pair<>(min, max);
   }
}

运行结果如下：

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> //定义Pair类，引入一个类型变量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//定义公共类
{
   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);//通过类名调用minmax方法
      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)  //加了上界约束的泛型方法
   {
      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);
   }
}

运行结果如下：

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//定义一个公共类
{
   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> //定义公共类，Pair类引入一个类型变量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 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)//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)//定义泛型变量的下界，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
   {
      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)//表示带有下界
   {
      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，表示任何类型
   {
      return p.getFirst() == null || p.getSecond() == null;
   }

   public static void swap(Pair<?> p) { swapHelper(p); }//无限定通配符，可以用任意Object对象调用原始的Pair类的setObject方法。

   public static <T> void swapHelper(Pair<T> p)
   {
      T t = p.getFirst();
      p.setFirst(p.getSecond());
      p.setSecond(t);
   }
}

运行结果如下：

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）。

程序总体结构：Main类和Student类

模块说明：Main类包含文件读取、抓错处理、case语句（选择操作）以及具体操作内容

Student类包含更改器访问器

困难与问题：抓错语句不熟练

import java.io.File;
import java.io.BufferedReader;
import java.util.Scanner;
import java.util.ArrayList;
import java.util.Arrays;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Collections;

public class Test {
    private static ArrayList<Student> studentlist;

    public static void main(String[] args) {
        studentlist = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        File file = new File("F：\\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
        }
        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");

            }
        }
    }

    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;
    }

}

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";
    }
}

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：jisuan类

模块说明：文件的写入，随机生成加减乘除四则运算，返回得分

问题与困难：除法的结果带小数时运算不准确；在txt文件中只能写入得分

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

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

        Scanner in = new Scanner(System.in);
        yunsuan counter = new yunsuan();
        PrintWriter out = null;
        try {
            out = new PrintWriter("text.txt");
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        int sum = 0;
        System.out.println("随机生成的四则运算类型");
        System.out.println("类型1：除法");
        System.out.println("类型2：乘法");
        System.out.println("类型3：加法");
        System.out.println("类型4：减法");

        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;
            Random rand = new Random();
            m = (int) rand.nextInt(4) + 1;
            System.out.println("随机生成的四则运算类型："+m);

            switch (m) {
            case 1:
                System.out.println(i + ": " + a + "/" + b + "=");

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

                double c0 = in.nextDouble();
                out.println(a + "/" + b + "=" + c0);
                if (c0 == counter.division(a, b)) {
                    sum += 10;
                    System.out.println("right!");
                } else {
                    System.out.println("error!");
                }

                break;

            case 2:
                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("right!");
                } else {
                    System.out.println("error!");
                }
                break;
            case 3:
                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("right!");
                } else {
                    System.out.println("error!");
                }
                break;
            case 4:
                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("right!");
                } else {
                    System.out.println("error!");
                }
                break;
            }
        }
        System.out.println("成绩" + sum);
        out.println("成绩:" + sum);
        out.close();
    }
}

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;}
    }

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

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

        Scanner in = new Scanner(System.in);
        yunsuan counter = new yunsuan();
        PrintWriter out = null;
        try {
            out = new PrintWriter("test.txt");
        } catch (FileNotFoundException e) {
            System.out.println("文件夹输出失败");
            e.printStackTrace();
        }

        int sum = 0;
        System.out.println("随机生成的四则运算类型");
        System.out.println("类型1：除法");
        System.out.println("类型2：乘法");
        System.out.println("类型3：加法");
        System.out.println("类型4：减法");

        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;
            Random rand = new Random();
            m = (int) rand.nextInt(4) + 1;
            System.out.println("随机生成的四则运算类型：" + m);

            switch (m) {
            case 1:
                a = b + (int) Math.round(Math.random() * 100);
                while(b == 0){
                    b = (int) Math.round(Math.random() * 100);
                }
                while(a % b != 0){
                    a = (int) Math.round(Math.random() * 100);

                }
                                //若生成的除法式子必须能整除，且满足分母为0的条件，则a一定要大于b，且a模b的结果要为0。
                System.out.println(i + ": " + a + "/" + b + "=");

                int c0 = in.nextInt();
                out.println(a + "/" + b + "=" + c0);
                if (c0 == counter.division(a, b)) {
                    sum += 10;
                    System.out.println("right!");
                } else {
                    System.out.println("error!");
                }

                break;

            case 2:
                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("right!");
                } else {
                    System.out.println("error!");
                }
                break;
            case 3:
                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("right!");
                } else {
                    System.out.println("error!");
                }
                break;
            case 4:
                while (a < b) {
                    b = (int) Math.round(Math.random() * 100);
                }
                                //因为不能产生运算结果为负数的减法式子，所以a一定要大于b。若a<b,则重新生成b。
                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("right!");
                } else {
                    System.out.println("error!");
                }
                break;
            }
        }
        System.out.println("成绩" + sum);
        out.println("成绩:" + sum);
        out.close();
    }
}

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;
        }

}

实验总结：本周学习了有关泛型的知识，泛型接口的定义与实现，学会运用泛型技术设计程序，了解泛型程序设计，理解其用途。但本周所学知识中通配符的运用理解还有待加强。