实验十 泛型程序设计技术
实验时间 2018-11-4
一、理论知识
1、JDK 5.0 中增加的泛型类型，是Java 语言中类型安全的一次重要改进。
2、 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。（如ArrayList类）
3、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。
4、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。
5、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。
6、 泛型类可以有多个类型变量。例如:public class Pair<T, U> { … }
7、 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。
8、 泛型方法
（1） 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。
（2） 泛型方法可以声明在泛型类中，也可以声明在普通类中。
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> //定义公共类，Pair类引入了一个类型变量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 pair1; /** * @version 1.01 2012-01-26 * @author Cay Horstmann */ public class PairTest1//定义公共类 { 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//另一个类 { /** * 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) { 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++)//for循环语句 { if (min.compareTo(a[i]) > 0) min = a[i]; if (max.compareTo(a[i]) < 0) max = a[i]; } return new Pair<>(min, max); } }
实验结果：
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(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) { 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); } }
实验结果：
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) { 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); } }
实验结果：
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：
类people
1、读入文件等
2、定义了查找人员信息的方法
3、分5个case来分别说年龄大小、等。
出现问题：
过程中出现了很多问题，主要原因还是在于自己的粗心和对一些知识的掌握不够，不过在和同学们的交流和学习中得以解决，以后我会接续努力的。
package gh; 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.Scanner; import java.util.Collections; public class tt { public static People findPeopleByname(String name) { People flag = null; for (People people : peoplelist) { if(people.getName().equals(name)) { flag = people; } } return flag; } public static People findPeopleByid(String id) { People flag = null; for (People people : peoplelist) { if(people.getnumber().equals(id)) { flag = people; } } return flag; } private static ArrayList<People> agenear(int yourage) { // TODO Auto-generated method stub int j=0,min=53,d_value=0,k = 0; ArrayList<People> plist = new ArrayList<People>(); for (int i = 0; i < peoplelist.size(); i++) { d_value = peoplelist.get(i).getage() > yourage ? peoplelist.get(i).getage() - yourage : yourage - peoplelist.get(i).getage() ; k = d_value < min ? i : k; min = d_value < min ? d_value : min; } for(People people : peoplelist) { if(people.getage() == peoplelist.get(k).getage()) { plist.add(people); } } return plist; } private static ArrayList<People> peoplelist; public static void main(String[] args) //throws IOException { peoplelist = new ArrayList<People>(); Scanner scanner = new Scanner(System.in); File file = new File("D:\身份证号.txt"); try { FileInputStream files = new FileInputStream(file); BufferedReader in = new BufferedReader(new InputStreamReader(files)); String temp = null; while ((temp = in.readLine()) != null) { String[] information = temp.split("[ ]+"); People people = new People(); people.setName(information[0]); people.setnumber(information[1]); int A = Integer.parseInt(information[3]); people.setage(A); people.setsex(information[2]); for(int j = 4; j<information.length;j++) { people.setplace(information[j]); } peoplelist.add(people); } } catch (FileNotFoundException e) { System.out.println("文件未找到"); e.printStackTrace(); } catch (IOException e) { System.out.println("文件读取错误"); e.printStackTrace(); } boolean isTrue = true; while (isTrue) { System.out.println("******************************************"); System.out.println(" 1.按姓名典序输出人员信息"); System.out.println(" 2.查询最大年龄人员信息"); System.out.println(" 3.查询最小年龄人员信息"); System.out.println(" 4.输入你的年龄，查询身份证号.txt中年龄与你最近的人"); System.out.println(" 5.查询人员中是否有你的同乡"); System.out.println(" 6.退出"); System.out.println("******************************************"); int nextInt = scanner.nextInt(); switch (nextInt) { case 1: Collections.sort(peoplelist); System.out.println(peoplelist.toString()); break; case 2: int max=0; int j,k1 = 0; for(int i=1;i<peoplelist.size();i++) { j = peoplelist.get(i).getage(); if(j>max) { max = j; k1 = i; } } System.out.println("年龄最大："+peoplelist.get(k1)); break; case 3: int min = 100; int j1,k2 = 0; for(int i=1;i<peoplelist.size();i++) { j1 = peoplelist.get(i).getage(); if(j1<min) { min = j1; k2 = i; } } System.out.println("年龄最小："+peoplelist.get(k2)); break; case 4: System.out.println("年龄："); int input_age = scanner.nextInt(); ArrayList<People> plist = new ArrayList<People>(); plist = agenear(input_age); for(People people : plist) { System.out.println(people.toString()); } break; case 5: System.out.println("请输入省份"); String find = scanner.next(); for (int i = 0; i <peoplelist.size(); i++) { String [] place = peoplelist.get(i).getplace().split(" "); for(String temp : place) { if(find.equals(temp)) { System.out.println("你的同乡是 "+peoplelist.get(i)); break; } } } break; case 6: isTrue = false; System.out.println("byebye!"); break; default: System.out.println("输入有误"); } } } } }
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：
类main
1、程序中的文件读取等
出现问题：
1.没有定义文件输出的路径，找输出文件不简单。
解决方法：只需定义路径即可如：
("E:\壁纸\海贼王\text.txt");
package rt; import java.io.FileNotFoundException; import java.io.PrintWriter; import java.util.Scanner; public class tt { public static void main(String[] args) { Scanner in = new Scanner(System.in); tt1 computing=new tt1(); PrintWriter output = null; try { output = new PrintWriter("tt.txt"); } catch (Exception e) { } int sum = 0; for (int i = 1; i < 11; i++) { int a = (int) Math.round(Math.random() * 100); int b = (int) Math.round(Math.random() * 100); int s = (int) Math.round(Math.random() * 3); switch(s) { case 1: System.out.println(i+": "+a+"/"+b+"="); while(b==0){ b = (int) Math.round(Math.random() * 100); } double c = in.nextDouble(); output.println(a+"/"+b+"="+c); if (c == (double)computing.division(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break; case 2: System.out.println(i+": "+a+"*"+b+"="); int c1 = in.nextInt(); output.println(a+"*"+b+"="+c1); if (c1 == computing.multiplication(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break; case 3: System.out.println(i+": "+a+"+"+b+"="); int c2 = in.nextInt(); output.println(a+"+"+b+"="+c2); if (c2 == computing.addition(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break ; case 4: System.out.println(i+": "+a+"-"+b+"="); int c3 = in.nextInt(); output.println(a+"-"+b+"="+c3); if (c3 == computing.subtraction(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break ; } } System.out.println("成绩："+sum+"分"); output.println("成绩："+sum+"分"); output.close(); } } class tt1 { private int a; private int b; public int addition(int a,int b) { return a+b; } public int subtraction(int a,int b) { if((a-b)<0) return 0; else 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。
package hh;
public class jj<T> {
private T a;
private T b;
public jj() {
a = null;
b = null;
}
public jj(T a, T b) {
this.a = a;
this.b = b;
}
public int jj1(int a,int b)
{
return a+b;
}
public int jj2(int a,int b)
{
return a-b;
}
public int jj3(int a,int b)
{
return a*b;
}
public int jj4(int a,int b)
{
if(b!=0)
return a/b;
else return 0;
}
}
package hh; import java.io.FileNotFoundException; import java.io.PrintWriter; import java.util.Scanner; public class kk { public static void main(String[] args) { Scanner in = new Scanner(System.in); jj counter=new jj(); PrintWriter out = null; try { out = new PrintWriter("E:\壁纸\海贼王\text.txt"); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } int sum = 0; for (int i = 0; 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() * 3); switch(m) { case 0: System.out.println(a + "+" + b + "="); int d0 = in.nextInt(); out.println(a + "+" + b + "=" + d0); if (d0 == counter.jj1(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break; case 1: while (a < b) { int x = a; a = b; b = x; } System.out.println(a + "-" + b + "="); int c1 = in.nextInt(); out.println(a + "-" + b + "=" + c1); if (c1 == counter.jj2(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break; case 2: System.out.println(a + "*" + b + "="); int c2 = in.nextInt(); out.println(a + "*" + b + "=" + c2); if (c2 ==counter.jj3(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break; case 3: while (b == 0 || a % b != 0) { a = (int) Math.round(Math.random() * 100); b = (int) Math.round(Math.random() * 100); } System.out.println(a + "/" + b + "="); int c3 = in.nextInt(); out.println(a + "/" + b + "=" + c3); if (c3 == counter.jj4(a, b)) { sum += 10; System.out.println("正确"); } else { System.out.println("错误"); } break; } } System.out.println("成绩"+sum); out.println("成绩:"+sum); out.close(); } }
实验结果：
实验总结：
本章我们主要学习了泛型程序设计，使用泛型机制编写的程序代码要比那些杂乱地使用Object变量，然后再进行强行类型转换的代码具有更好的安全性和可读性。反省对于集合类尤其有用。通过课后一些简单程序的编译，运行，知道了如何定义简单的泛型类，和他的一些用法。希望在以后的编程中我会多多的用到这些学过的知识。