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；
泛型：也称参数化类型，就是在定义类，接口和方法时，通过类型参数只是将要处理的类型对象。（如ArrayList类）
(2) 掌握泛型类的定义与使用；
一个泛型类，就是具有一个或者多个类型变量的类，即创建用类型作为参数的类。一个泛型类定义格式如下：
class Generics(K,V);
其中K和V是类中的可变类型的参数。
(3) 掌握泛型方法的声明与使用；
泛型方法：除了泛型类之外，还可以只单独定义一个方法作为泛型方法，用于指定泛型参数或者返回值为泛型类型。，留待方法调用时确定。
泛型方法可以声明在泛型类中，也可以声明在普通类中。
public class ArrayTool
{
public static <E> void insert (E[] ,int i)
{
......
}
Public static<E> E valueAt(E[] e,int i)
{
...
}
}
(4) 掌握泛型接口的定义与实现；
定义：
public interface IPool<T>
{
T get();
Int add(T t);
}
实现：
public class GenericPool<T> implements IPool<T>
{
...
}
public class GenericPool implements IPool<Account>
{
...
}
(5)了解泛型程序设计，理解其用途。
泛类型程序设计：编写代码可以被许多不同类型的对象使用。
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> //T是类型变量
{
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" };//初始化一个String类型的数组
Pair<String> mm = ArrayAlg.minmax(words);//通过类名调用minmax方法。
//minmax的返回值是Pair<String>类型的
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)//定义静态方法minmax
//实例化以后的Pair对象（普通方法）
{
if (a == null || a.length == 0) return null;
String min = a[0];
String max = a[0];
for (int i = 1; i < a.length; i++)//length：String类数组a[]的一个属性
{
if (min.compareTo(a[i]) > 0) min = a[i];//compareTo：数组的遍历，通过Ascll码进行比较
if (max.compareTo(a[i]) < 0) max = a[i];
//按照字典排序（比较的是字母的ascll编码，大写字母的值比较小
}
return new Pair<>(min, max);//返回一个Pair类型的对象。（将这两个数据打包）
}
}
运行结果：
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；
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)
{
//初始化一个LocalDate类数组，数组名为birthdays
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);//静态方法，可以通过类名调用
System.out.println("min = " + mm.getFirst());
System.out.println("max = " + mm.getSecond());
}
} class ArrayAlg//泛型类
{
/**
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)//泛型方法
//使用extends关键字为类型变量设置上界
{
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：
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 1.00 2004-05-10
* @author Cay Horstmann
*/
public class Pair<T>
{
private T first;
private T second; public Pair()//无参数构造器
{
first = null; second = null;//必须设置为null，否则会出现空指针异常
}
public Pair(T first, T second)//构造器含参数，first和second不必置空
{
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)
{
//创建了manger类对象
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)
//Pair<? extends Employee>表示任何泛型Pair类型，它的类型参数是Emplooy的子类。? 通配符
{
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 swapHelper通配符类型
}
// 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; 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;
}
}
运行结果：
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）。
程序结构：
Indentity 和 使用了接口的Student类
package 小陈9;
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 ) {
this.age=age ;
}
public String getprovince() {
return province;
}
public void setprovince(String province) {
this.province=province ;
}
@Override
public int compareTo(Student other) {
// TODO Auto-generated method stub
return this.name.compareTo(other.getName());
}//compareTo方法比较姓名
public String toString() {
return name+"\t"+sex+"\t"+age+"\t"+number+"\t"+province+"\n";
}
}
package 小陈9;
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 Identity{
private static ArrayList<Student> studentlist;
public static void main(String[] args) {
studentlist = new ArrayList<>();
Scanner scanner = new Scanner(System.in);
File file = new File("C:/身份证号.txt");
try {
//利用try 。。 catch 语句进行异常处理
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();
} catch (IOException e) {
System.out.println("学生信息文件读取错误");
e.printStackTrace();
//捕获异常
}
//读取文件内容
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("1.字典排序");
System.out.println("2.输出年龄最大和年龄最小的人");
System.out.println("3.寻找老乡");
System.out.println("4.寻找年龄相近的人");
System.out.println("0.退出");
int status = scanner.nextInt();
switch (status) {
case 1:
Collections.sort(studentlist); //对姓名字典排序
System.out.println(studentlist.toString());
break;
case 2:
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 3:
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 4:
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 0:
status = 0;
System.out.println("程序已退出!");
break;
default:
System.out.println("输入错误");
}
}
}//选择具体操作
public static int agenear(int age) {
int 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;
}//找到年龄最大和最小者 }
程序设计存在的困难与问题:
（1）编程能力差，对代码的熟悉和了解远远不够，应该多加练习。
（2）看到问题不会分析，不能很快从中提取出主要的变量和要进行的操作
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）。
程序结构：
yunsuan类 和 jieguo类
public class yunsuan {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
Pair student=new Pair();
PrintWriter out = null;
try {
out = new PrintWriter("text.txt");
} catch (FileNotFoundException e) {
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 c= (int) Math.round(Math.random() * 3);
//生成随机数 , 用于生成四则运算题目 ,其中c 用于switch语句，生成四则运算的种类
switch(c)
{
case 0:
System.out.println(i+": "+a+"/"+b+"=");
while(b==0)
{
b = (int) Math.round(Math.random() * 100);
}
int C = in.nextInt();
out.println(a+"/"+b+"="+C);
if (C == student.division(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
}
break;
case 1:
System.out.println(i+": "+a+"*"+b+"=");
int D = in.nextInt();
out.println(a+"*"+b+"="+D);
if (D == student.multiply(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
}
break;
case 2:
System.out.println(i+": "+a+"+"+b+"=");
int E = in.nextInt();
out.println(a+"+"+b+"="+E);
if (E == student.plus(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
}
break ;
case 3:
System.out.println(i+": "+a+"-"+b+"=");
int F = in.nextInt();
out.println(a+"-"+b+"="+F);
if (F == student.minus(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
}
break ;
}
}//生成四则运算题目，并判断回答是否正确
System.out.println("成绩"+sum);
out.println("成绩:"+sum);
out.close();
//输出结果
} }
*public class jieguo {
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;
}
}
程序设计存在的困难与问题：
（1）text文件的输出存在问题
（2）接口应用存在问题，对于使用接口设计程序不能熟练掌握。
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 小陈1;
public class Pair<T> {
private T a;
private T b;
public Pair()
{
a = null;
b = null;
}
public Pair(T a,T b)
{
this.a = a;
this.b = b;
}
public T getA()
{
return a;
}
public T getB()
{
return b;
}
public int plus(int a,int b)
{
return a+b;
}
public int minus(int a,int b)
{
return a-b;
}
public int multiply(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;
}
}
package 小陈1; import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner; public class yunsuan {
public static void main(String[] args) { Scanner in = new Scanner(System.in);
Pair student=new Pair();
PrintWriter out = null;
try {
out = new PrintWriter("text.txt");
} catch (FileNotFoundException e) {
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 c= (int) Math.round(Math.random() * 3); switch(c)
{
case 0:
System.out.println(i+": "+a+"/"+b+"="); while(b==0)
{
b = (int) Math.round(Math.random() * 100);
} int C = in.nextInt();
out.println(a+"/"+b+"="+C);
if (C == student.division(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
} break; case 1:
System.out.println(i+": "+a+"*"+b+"=");
int D = in.nextInt();
out.println(a+"*"+b+"="+D);
if (D == student.multiply(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
}
break;
case 2:
System.out.println(i+": "+a+"+"+b+"=");
int E = in.nextInt();
out.println(a+"+"+b+"="+E);
if (E == student.plus(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
} break ;
case 3:
System.out.println(i+": "+a+"-"+b+"=");
int F = in.nextInt();
out.println(a+"-"+b+"="+F);
if (F == student.minus(a, b)) {
sum += 10;
System.out.println("right");
}
else {
System.out.println("false");
}
break ;
}
}//生成四则运算题目，并判断回答是否正确
System.out.println("成绩"+sum);
out.println("成绩:"+sum);
out.close();
}
}
总结：本周学习了泛类型程序设计，了解到泛型的主要目标是实现Java的类型安全。其主要使用在类，接口，方法中。提高了代码的重用性。存在的问题在于对泛型程序设计的使用不太熟练，还需要继续进行学习。