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。
1 package pair1; 2 3 /** 4 * @version 1.00 2004-05-10 5 * @author Cay Horstmann 6 */ 7 public class Pair<T>//Pair类引入了一个类型变量T，用尖括号括起来 8 9 { 10 private T first; 11 private T second; 12 //指方法的返回类型以及域和局部变量的类型 13 public Pair() { first = null; second = null; } 14 public Pair(T first, T second) { this.first = first; this.second = second; } 15 16 public T getFirst() { return first; } 17 public T getSecond() { return second; } 18 19 public void setFirst(T newValue) { first = newValue; } 20 public void setSecond(T newValue) { second = newValue; } 21 }
1 package pair1; 2 3 /** 4 * @version 1.01 2012-01-26 5 * @author Cay Horstmann 6 */ 7 public class PairTest1 8 { 9 public static void main(String[] args) 10 { 11 String[] words = { "Mary", "had", "a", "little", "lamb" }; 12 Pair<String> mm = ArrayAlg.minmax(words); 13 System.out.println("min = " + mm.getFirst()); 14 System.out.println("max = " + mm.getSecond()); 15 } 16 } 17 18 class ArrayAlg 19 { 20 /** 21 * Gets the minimum and maximum of an array of strings. 22 * @param a an array of strings 23 * @return a pair with the min and max value, or null if a is null or empty 24 */ 25 public static Pair<String> minmax(String[] a)//使用静态方法来用泛型方法 26 { 27 if (a == null || a.length == 0) return null; 28 String min = a[0]; 29 String max = a[0]; 30 for (int i = 1; i < a.length; i++) 31 { 32 if (min.compareTo(a[i]) > 0) min = a[i]; 33 if (max.compareTo(a[i]) < 0) max = a[i]; 34 } 35 return new Pair<>(min, max); 36 } 37 }
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。
1 package pair2; 2 3 import java.time.*; 4 5 /** 6 * @version 1.02 2015-06-21 7 * @author Cay Horstmann 8 */ 9 public class PairTest2 10 { 11 public static void main(String[] args) 12 { 13 LocalDate[] birthdays = 14 { 15 LocalDate.of(1906, 12, 9), // G. Hopper 16 LocalDate.of(1815, 12, 10), // A. Lovelace 17 LocalDate.of(1903, 12, 3), // J. von Neumann 18 LocalDate.of(1910, 6, 22), // K. Zuse 19 }; 20 Pair<LocalDate> mm = ArrayAlg.minmax(birthdays); 21 System.out.println("min = " + mm.getFirst()); 22 System.out.println("max = " + mm.getSecond()); 23 } 24 } 25 26 class ArrayAlg 27 { 28 /** 29 Gets the minimum and maximum of an array of objects of type T. 30 @param a an array of objects of type T 31 @return a pair with the min and max value, or null if a is 32 null or empty 33 */ 34 public static <T extends Comparable> Pair<T> minmax(T[] a) 35 { 36 if (a == null || a.length == 0) return null; 37 T min = a[0]; 38 T max = a[0]; 39 for (int i = 1; i < a.length; i++) 40 { 41 if (min.compareTo(a[i]) > 0) min = a[i]; 42 if (max.compareTo(a[i]) < 0) max = a[i]; 43 } 44 return new Pair<>(min, max); 45 } 46 }
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; } }
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 1.01 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) { 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) { 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) { 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); } }
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; } }
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）。
1 package test1; 2 3 import java.io.BufferedReader; 4 import java.io.File; 5 import java.io.FileInputStream; 6 import java.io.FileNotFoundException; 7 import java.io.IOException; 8 import java.io.InputStreamReader; 9 import java.util.ArrayList; 10 import java.util.Collections; 11 import java.util.Scanner; 12 13 public class Main{ 14 private static ArrayList<Student> studentlist; 15 public static void main(String[] args) { 16 studentlist = new ArrayList<>(); 17 Scanner scanner = new Scanner(System.in); 18 File file = new File("F:\身份证号.txt"); 19 try { 20 FileInputStream fis = new FileInputStream(file); 21 BufferedReader in = new BufferedReader(new InputStreamReader(fis)); 22 String temp = null; 23 while ((temp = in.readLine()) != null) { 24 25 Scanner linescanner = new Scanner(temp); 26 27 linescanner.useDelimiter(" "); 28 String name = linescanner.next(); 29 String number = linescanner.next(); 30 String sex = linescanner.next(); 31 String age = linescanner.next(); 32 String province =linescanner.nextLine(); 33 Student student = new Student(); 34 student.setName(name); 35 student.setnumber(number); 36 student.setsex(sex); 37 int a = Integer.parseInt(age); 38 student.setage(a); 39 student.setprovince(province); 40 studentlist.add(student); 41 42 } 43 } catch (FileNotFoundException e) { 44 System.out.println("学生信息文件找不到"); 45 e.printStackTrace(); 46 } catch (IOException e) { 47 System.out.println("学生信息文件读取错误"); 48 e.printStackTrace(); 49 } 50 boolean isTrue = true; 51 while (isTrue) { 52 System.out.println("选择你的操作，输入正确格式的选项"); 53 System.out.println("A.按姓名字典排序"); 54 System.out.println("B.输出年龄最大和年龄最小的人"); 55 System.out.println("C.寻找老乡"); 56 System.out.println("D.寻找年龄相近的人"); 57 System.out.println("F.退出"); 58 String m = scanner.next(); 59 switch (m) { 60 case "A": 61 Collections.sort(studentlist); 62 System.out.println(studentlist.toString()); 63 break; 64 case "B": 65 int max=0,min=100; 66 int j,k1 = 0,k2=0; 67 for(int i=1;i<studentlist.size();i++) 68 { 69 j=studentlist.get(i).getage(); 70 if(j>max) 71 { 72 max=j; 73 k1=i; 74 } 75 if(j<min) 76 { 77 min=j; 78 k2=i; 79 } 80 81 } 82 System.out.println("年龄最大："+studentlist.get(k1)); 83 System.out.println("年龄最小："+studentlist.get(k2)); 84 break; 85 case "C": 86 System.out.println("老家?"); 87 String find = scanner.next(); 88 String place=find.substring(0,3); 89 for (int i = 0; i <studentlist.size(); i++) 90 { 91 if(studentlist.get(i).getprovince().substring(1,4).equals(place)) 92 System.out.println("老乡"+studentlist.get(i)); 93 } 94 break; 95 96 case "D": 97 System.out.println("年龄："); 98 int yourage = scanner.nextInt(); 99 int near=agenear(yourage); 100 int value=yourage-studentlist.get(near).getage(); 101 System.out.println(""+studentlist.get(near)); 102 break; 103 case "F": 104 isTrue = false; 105 System.out.println("退出程序!"); 106 break; 107 default: 108 System.out.println("输入有误"); 109 110 } 111 } 112 } 113 public static int agenear(int age) { 114 int j=0,min=53,value=0,k=0; 115 for (int i = 0; i < studentlist.size(); i++) 116 { 117 value=studentlist.get(i).getage()-age; 118 if(value<0) value=-value; 119 if (value<min) 120 { 121 min=value; 122 k=i; 123 } 124 } 125 return k; 126 } 127 128 }
1 package test1; 2 3 public class Student implements Comparable<Student> { 4 5 private String name; 6 private String number ; 7 private String sex ; 8 private int age; 9 private String province; 10 11 public String getName() { 12 return name; 13 } 14 public void setName(String name) { 15 this.name = name; 16 } 17 public String getnumber() { 18 return number; 19 } 20 public void setnumber(String number) { 21 this.number = number; 22 } 23 public String getsex() { 24 return sex ; 25 } 26 public void setsex(String sex ) { 27 this.sex =sex ; 28 } 29 public int getage() { 30 31 return age; 32 } 33 public void setage(int age) { 34 // int a = Integer.parseInt(age); 35 this.age= age; 36 } 37 38 public String getprovince() { 39 return province; 40 } 41 public void setprovince(String province) { 42 this.province=province ; 43 } 44 45 public int compareTo(Student o) { 46 return this.name.compareTo(o.getName()); 47 } 48 49 public String toString() { 50 return name+" "+sex+" "+age+" "+number+" "+province+" "; 51 } 52 }
总体结构：
程序有一个主类和一个子类。
模块说明：
主类涉及到对文件的读入操作，所以要用try...catch语句进行异常处理。还有选择语句。
子类是对接口Comparable的实现。主要用来返回学生的信息。
目前程序设计的困难：
对文件的读写操作不熟悉，不知道如何进行排序以及查找。
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）。
1 package shiyan; 2 import java.util.Scanner; 3 import java.io.PrintWriter; 4 5 public class Main { 6 public static void main(String[] args) throws Exception{ 7 Scanner in=new Scanner(System.in); 8 PrintWriter output=new PrintWriter("E:/test.txt"); 9 int sum=0; 10 jisuanji js=new jisuanji(); 11 for (int i = 0; i < 10; i++) { 12 int a = (int) Math.round(Math.random() * 100); 13 int b = (int) Math.round(Math.random() * 100); 14 int n = (int) Math.round(Math.random() * 3); 15 16 switch(n) 17 { 18 case 1: 19 System.out.println(a+"/"+b+"="); 20 while(b==0){ 21 b = (int) Math.round(Math.random() * 100); 22 } 23 double c = in.nextDouble(); 24 output.println(a+"/"+b+"="+c); 25 if (c == js.chu(a,b)) { 26 sum += 10; 27 System.out.println("答案正确"); 28 } 29 else { 30 System.out.println("答案错误"); 31 } 32 33 break; 34 35 case 2: 36 System.out.println(a+"*"+b+"="); 37 int c1 = in.nextInt(); 38 output.println(a+"*"+b+"="+c1); 39 if (c1 == js.chen(a, b)) { 40 sum += 10; 41 System.out.println("答案正确"); 42 } 43 else { 44 System.out.println("答案错误"); 45 } 46 break; 47 case 3: 48 System.out.println(a+"+"+b+"="); 49 int c2 = in.nextInt(); 50 output.println(a+"+"+b+"="+c2); 51 if (c2 == js.jia(a, b)) { 52 sum += 10; 53 System.out.println("答案正确"); 54 } 55 else { 56 System.out.println("答案错误"); 57 } 58 59 break ; 60 case 4: 61 System.out.println(a+"-"+b+"="); 62 int c3 = in.nextInt(); 63 output.println(a+"-"+b+"="+c3); 64 if (c3 == js.jian(a,b)) { 65 sum += 10; 66 System.out.println("答案正确"); 67 } 68 else { 69 System.out.println("答案错误"); 70 } 71 break ; 72 73 } 74 75 } 76 System.out.println("成绩"+sum); 77 output.println("成绩:"+sum); 78 output.close(); 79 } 80 }
1 package shiyan; 2 3 public class jisuanji { 4 private int a; 5 private int b; 6 public int jia(int a,int b) 7 { 8 return a+b; 9 } 10 public int jian(int a,int b) 11 { 12 return a-b; 13 } 14 public int chen(int a,int b) 15 { 16 return a*b; 17 } 18 public int chu(int a,int b) 19 { 20 if(b==0) 21 { 22 return 0; 23 } 24 else 25 return a/b; 26 } 27 }
总体结构：有一个主类和一个子类。
模块说明：主类里涉及文件的输出和异常处理，子类是实现计算器功能的算法。
困难：不熟悉写出到文件的操作，导致程序编写困难。生成的减法和除法运算题不适应小学生的能力。
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。
1 package shiyan; 2 import java.util.Scanner; 3 import java.io.FileNotFoundException; 4 import java.io.PrintWriter; 5 6 public class Main { 7 public static void main(String[] args) { 8 Scanner in=new Scanner(System.in); 9 PrintWriter output = null; 10 try { 11 output = new PrintWriter("E:/test.txt"); 12 } catch (FileNotFoundException e) { 13 // TODO 自动生成的 catch 块 14 System.out.println("文件输出失败"); 15 e.printStackTrace(); 16 } 17 int sum=0; 18 jisuanji js=new jisuanji(); 19 for (int i = 0; i < 10; i++) { 20 int a = (int) Math.round(Math.random() * 100); 21 int b = (int) Math.round(Math.random() * 100); 22 int n = (int) Math.round(Math.random() * 4 ); 23 24 switch(n) 25 { 26 case 1: 27 System.out.println(a+"/"+b+"="); 28 while(b==0){ 29 b = (int) Math.round(Math.random() * 100); 30 } 31 while(a%b!=0) { 32 a = (int) Math.round(Math.random() * 100); 33 b = (int) Math.round(Math.random() * 100); 34 } 35 double c = in.nextDouble(); 36 output.println(a+"/"+b+"="+c); 37 if (c == js.chu(a,b)) { 38 sum += 10; 39 System.out.println("答案正确"); 40 } 41 else { 42 System.out.println("答案错误"); 43 } 44 45 break; 46 47 case 2: 48 System.out.println(a+"*"+b+"="); 49 int c1 = in.nextInt(); 50 output.println(a+"*"+b+"="+c1); 51 if (c1 == js.chen(a, b)) { 52 sum += 10; 53 System.out.println("答案正确"); 54 } 55 else { 56 System.out.println("答案错误"); 57 } 58 break; 59 case 3: 60 System.out.println(a+"+"+b+"="); 61 int c2 = in.nextInt(); 62 output.println(a+"+"+b+"="+c2); 63 if (c2 == js.jia(a, b)) { 64 sum += 10; 65 System.out.println("答案正确"); 66 } 67 else { 68 System.out.println("答案错误"); 69 } 70 71 break ; 72 case 4: 73 System.out.println(a+"-"+b+"="); 74 while(a<b) { 75 a = (int) Math.round(Math.random() * 100); 76 b = (int) Math.round(Math.random() * 100); 77 } 78 int c3 = in.nextInt(); 79 output.println(a+"-"+b+"="+c3); 80 if (c3 == js.jian(a,b)) { 81 sum += 10; 82 System.out.println("答案正确"); 83 } 84 else { 85 System.out.println("答案错误"); 86 } 87 break ; 88 89 } 90 91 } 92 System.out.println("成绩"+sum); 93 output.println("成绩:"+sum); 94 output.close(); 95 } 96 }
1 package shiyan; 2 3 public class jisuanji<T> { 4 private T a; 5 private T b; 6 public jisuanji() { 7 a=null; 8 b=null; 9 } 10 public jisuanji(T a,T b) { 11 this.a=a; 12 this.b=b; 13 } 14 public int jia(int a,int b) 15 { 16 return a+b; 17 } 18 public int jian(int a,int b) 19 { 20 return a-b; 21 } 22 public int chen(int a,int b) 23 { 24 return a*b; 25 } 26 public int chu(int a,int b) 27 { 28 if(b!=0&&a%b==0) 29 return a/b; 30 else 31 return 0; 32 } 33 }
实验总结：
这次实验加深了对实验9编程题的理解，改进了其中的错误。学会了泛型类的设计，但是通配符还是有些不理解的地方。