一、理論知識部分

泛型：也稱參數化類型，就是在定義類、接口和方法時，通過類型參數指示將要處理的對象類型。（如ArrayList類）

泛型程序設計（Generic programming）：編寫代碼可以被很多不同類型的對象所重用。

一個泛型類（generic class）就是具有一個或多個類型變量的類，即創建用類型作為參數的類。如一個泛型類定義格式如下： class Generics＜K,V＞其中的K和V是類中的可變類型參數。

泛型類可以有多個類型變量。例如: public class Pair<t, u=""> <T,U>{ … }

類定義中的類型變量用於指定方法的返回類型以及域、局部變量的類型。

泛型方法：除了泛型類外，還可以只單獨定義一個方法作為泛型方法，用於指定方法參數或者返回值為泛型類型，留待方法調用時確定。泛型方法可以聲明在泛型類中，也可以聲明在 普通類中。

extends關鍵字所聲明的上界既可以是一個類，也可以是一個接口

<T extends Bounding Type>表示T應該是綁定類型的子類型。一個類型變量或通配符可以有多個限定，限定類型用“&”分割。

泛型變量下界:通過使用super關鍵字可以固定泛型參數的類型為某種類型或者其超類。當程序希望為一個方法的參數限定類型時，通常可以使用下限通配符

通配符：“？”符號表明參數的類型可以是任何一種類型，它和參數T的含義是有區別的。T表示一種未知類型，而“？”表示任何一種類型。這種通配符一般有以下三種用法：單獨的？：用於表示任何類型。 ? extends type：表示帶有上界。 ? super type：表示帶有下界。

二、實驗部分

1、實驗目的與要求

(1) 理解泛型概念；

(2) 掌握泛型類的定義與使用；

(3) 掌握泛型方法的聲明與使用；

(4) 掌握泛型接口的定義與實現；

(5)了解泛型程序設計，理解其用途。

2、實驗內容和步驟

實驗1： 導入第8章示例程序，測試程序並進行代碼註釋。

測試程序1：

l 編輯、調試、運行教材311、312頁 代碼，結合程序運行結果理解程序；

l 在泛型類定義及使用代碼處添加註釋；

l 掌握泛型類的定義及使用

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" };//泛型對象是字符串對象
      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)//用具體的類型替換類型變量可以實例化泛型類型
   {
      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);
   }
}

測試程序2：

l 編輯、調試運行教材315頁 PairTest2，結合程序運行結果理解程序；

l 在泛型程序設計代碼處添加相關註釋；

l 掌握泛型方法、泛型變量限定的定義及用途。

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) //通過對類型變量T設置限定，將T限制為實現了Comparable接口的類
   {
      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);
   }
}

測試程序3：

l 用調試運行教材335頁 PairTest3，結合程序運行結果理解程序；

l 了解通配符類型的定義及用途。

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());
   }
//打印雇員對的方法
   public static void printBuddies(Pair<? extends Employee> p)//使用通配符類型，表示帶有上界。
   {
      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)//表示帶有下界。
   {
      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)//無限定的通配符
   {
      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);
   }
}

實驗2：編程練習：

編程練習1：實驗九編程題總結

l 實驗九編程練習1總結（從程序總體結構說明、模塊說明，目前程序設計存在的困難與問題三個方面闡述）。

總體結構：主類Main 子類Person

模塊說明：Main：查找文件，對文件進行讀取。

Person：對文件進行具體的處理

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 + "\t" + sex + "\t" + age + "\t" + ID + "\t" + birthplace + "\n";
    }
}

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("身份證號.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("信息讀取有誤");
            e.printStackTrace();
        }
        boolean isTrue = true;
        while (isTrue) {
            System.out.println("1:按姓名字典序輸出人員信息");
            System.out.println("2:查詢最大年齡與最小年齡人員信息");
            System.out.println("3：按省份找同鄉");
            System.out.println("4:輸入你的年齡,查詢年齡與你最近人的信息");
            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("年齡最大：" + Personlist.get(k1));
                System.out.println("年齡最小：" + 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("同鄉 " + Personlist.get(i));

                }

                break;
            case 4:
                System.out.println("年齡：");
                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("歡迎使用!");
                break;
            default:
                System.out.println("輸入有誤");
            }
        }
    }

    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;
    }
}

問題：查找不到文件，代碼編程不是太會

l 實驗九編程練習2總結（從程序總體結構說明、模塊說明，目前程序設計存在的困難與問題三個方面闡述）。

總體結構：主類：Main 子類：math

模塊說明：Main：隨機生成十道100內的計算題，並判斷答案正誤

math：對具體計算進行處理

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("恭喜答案正確");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案錯誤");
                }

                break;

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

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

            }

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

問題：不符合小學四則運算要求，有的計算結果出現了負數

編程練習2：采用泛型程序設計技術改進實驗九編程練習2，使之可處理實數四則運算，其他要求不變。

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("恭喜答案正確");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案錯誤");
                }

                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("恭喜答案正確");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案錯誤");
                }
                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("恭喜答案正確");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案錯誤");
                }

                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("恭喜答案正確");
                    sum += 10;
                } else {
                    System.out.println("抱歉，答案錯誤");
                }
                break;

            }

        }
        System.out.println("成績" + sum);
        output.println("成績" + 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：實驗總結:

通過這次實驗，我了解了泛型類，泛型方法、通配符、泛型變量上界、泛型變量下界。通過對之前實驗的總結，對之前的知識進行進一步的回顧，通過改進代碼更好的了解了泛型程序設計。編程仍需多加練習，對之前的知識需要多加復習鞏固。

徐思201771010132《面向對象程序設計（java）》第十周學習總結