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。
一、理论知识
泛型类的定义:
(1)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型。
(2)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>
(3)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。
泛型变量的限定:
(1)extends关键字所声明的上界既可以是一个类,也可以是一个接口;
(2)<T extends Bounding Type>表示T应该是绑定类型的子类型。
泛型变量下界的说明:
– 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
– 当程序希望为一个方法的参数限定类型时,通常可以使
用下限通配符
泛型类的约束与局限性:
不能用基本类型实例化类型参数
运行时类型查询只适用于原始类型
不能抛出也不能捕获泛型类实例
参数化类型的数组不合法不能实例化类型变量
泛型类的静态上下文中类型变量无效
注意擦除后的冲突
通配符类型:
“?”符号表明参数的类型可以是任何一种类型,它和参数T的含义是有区别的。T表示一种未知类型,而“?”表示任何一种类型.
这种通配符一般有以下三种用法:
单独的?,用于表示任何类型。
? extends type,表示带有上界。
? super type,表示带有下界。
二、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类引入了一个类型变量T { private T first;//use the type variable private T second; public Pair() { first = null; second = null; } public Pair(T first, T second) { this.first = first; this.second = second; }//构造方法的调用 public T getFirst() { return first; }//返回值 public T getSecond() { return second; } public void setFirst(T newValue) { first = newValue; }//入口参数 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" };//定义常量 Pair<String> mm = ArrayAlg.minmax(words);//类名调用方法名 System.out.println("min = " + mm.getFirst()); System.out.println("max = " + mm.getSecond());//输出最大值、最小值 } } 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)//泛型类实例化 { 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];//compareTo比较方法 if (max.compareTo(a[i]) < 0) max = a[i]; } return new Pair<>(min, max);//实例化后的调用对象 } }
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;
掌握泛型方法、泛型变量限定的定义及用途。
package pair1; /** * @version 1.00 2004-05-10 * @author Cay Horstmann */ public class Pair<T>//Pair类引入了一个类型变量T { private T first;//use the type variable private T second; public Pair() { first = null; second = null; } public Pair(T first, T second) { this.first = first; this.second = second; }//构造方法的调用 public T getFirst() { return first; }//返回值 public T getSecond() { return second; } public void setFirst(T newValue) { first = newValue; }//入口参数 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);//实例化一个LocalDat类 System.out.println("min = " + mm.getFirst()); System.out.println("max = " + mm.getSecond());//得到min、max } } 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) //将T限制为实现Comparable接口的类 { if (a == null || a.length == 0) return null; T min = a[0]; T max = a[0]; for (int i = 1; i < a.length; i++)//compareTo方法 { if (min.compareTo(a[i]) > 0) min = a[i]; if (max.compareTo(a[i]) < 0) max = a[i]; } return new Pair<>(min, max);//返回新的pair类 } }
结果如下:
测试程序3:
用调试运行教材335页 PairTest3,结合程序运行结果理解程序;
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) { //定义Manager类 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<>();//程序调用泛型方法 minmaxBonus(managers, result);//泛型方法 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) //任何泛型Pair类型,它的类型参数是Manager的子类 { 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)//统配符限制为Manager的所有超类型 { 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)//泛型类;类型变量的通配符“?” { return p.getFirst() == null || p.getSecond() == null; } public static void swap(Pair<?> p) { swapHelper(p); } //swap调用swapHelper public static <T> void swapHelper(Pair<T> p) { T t = p.getFirst(); p.setFirst(p.getSecond()); p.setSecond(t); } }
Employee:
package pair3; import java.time.*; public class Employee //构造一个Employee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直接引用 this.salary = salary; hireDay = LocalDate.of(year, month, day); } //访问器方法 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; } }
Manager:
package pair3; public class Manager extends Employee//Manager类的父类是Employee类 { 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; } }l
结果如下:
实验2:编程练习:
编程练习1:实验九编程题总结
- 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)。
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; @SuppressWarnings("unused") public class Main{ private static ArrayList<Person> Personlist; @SuppressWarnings("resource") public static void main(String[] args) { Personlist = new ArrayList<>(); Scanner scanner = new Scanner(System.in); File file = new File("E:\\新建文件夹\\身份证号.txt"); //捕获代码 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("信息读取有误"); e.printStackTrace(); } boolean isTrue = true; while (isTrue) { System.out.println("————————————————————————————————————————"); System.out.println("1:按姓名字典序输出人员信息"); System.out.println("2:查询最大年龄人员信息和最小年龄人员信息"); System.out.println("3:输入你的年龄,查询年龄与你最近人的所有信息"); System.out.println("4:查询人员中是否有你的同乡"); 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("年龄最大:"+Personlist.get(k1)); System.out.println("年龄最小:"+Personlist.get(k2)); break; case 3: System.out.println("place?"); 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(""+Personlist.get(i)); } break; case 4: System.out.println("年龄:"); int yourage = scanner.nextInt(); int near=agenear(yourage); int d_value=yourage-Personlist.get(near).getage(); System.out.println(""+Personlist.get(near)); /* for (int i = 0; i < Personlist.size(); i++) { int p=Personlist.get(i).getage()-yourage; if(p<0) p=-p; if(p==d_value) System.out.println(Personlist.get(i)); } */ break; case 5: 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,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; } }
Main
程序总体结构:总体分为Main类和Person类
Main类:
1、将人员身份信息导入代码中
2、编辑了查找人员信息的方法
3、分5个case来分别说年龄大小、同乡等消息
Person类:
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) { // int a = Integer.parseInt(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"; } }
Person
对各个小模块进行具体的分析
程序设计存在的困难与问题:
1、编写时基础错误还是很多
2、Main类和Person类的变量名有时不能统一
- 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:Demo主类和Counter类
模块说明:Demo主类
import java.io.FileNotFoundException; import java.io.PrintWriter; import java.util.Scanner; public class Demo { public static void main(String[] args) { Scanner in = new Scanner(System.in); jf counter=new jf(); PrintWriter out = null; try { out = 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() * 3); switch(m) { case 0: System.out.println(i+": "+a+"/"+b+"="); while(b==0){ b = (int) Math.round(Math.random() * 100); } int c0 = in.nextInt(); out.println(a+"/"+b+"="+c0); if (c0 == jf.division(a, b)) { sum += 10; System.out.println("恭喜答案正确"); } else { System.out.println("抱歉,答案错误"); } break; case 1: 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("恭喜答案正确"); } else { System.out.println("抱歉,答案错误"); } break; case 2: 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("恭喜答案正确"); } else { System.out.println("抱歉,答案错误"); } break ; case 3: 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("恭喜答案正确"); } else { System.out.println("抱歉,答案错误"); } break ; } } System.out.println("成绩"+sum); out.println("成绩:"+sum); out.close(); } }
Demo
1、判断答案的正确性代码
2、文件的读取
3、四则运算代码的具体呈现
Counter类
public class Counter { 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; } }
Counter
四则运算的计算过程及返回值
程序设计存在的困难与问题:
1、数值过大,无法口算
2、运算复杂,不符合基础运算难度
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 C; import java.io.FileNotFoundException; import java.io.PrintWriter; import java.util.Random; import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner in = new Scanner(System.in); Suanfa counter = new Suanfa(); 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; 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.d(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 c = in.nextInt(); out.println(a + "*" + b + "=" + c); if (c == counter.m(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 c1 = in.nextInt(); out.println(a + "+" + b + "=" + c1); if (c1 == counter.add(a, b)) { sum += 10; System.out.println("正确!"); } else { System.out.println("错误!"); } 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.r(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(); } }
Main
package C; public class Suanfa<T> { private T a; private T b; public int add(int a,int b) { return a + b; } public int r(int a, int b) { return a - b; } public int m(int a, int b) { return a * b; } public int d(int a, int b) { if (b != 0 && a%b==0) return a / b; else return 0; } }
Suanfa
结果如下:
三、总结如下:
本章我们学习了泛型程序设计技术,首先理解了泛型概念,掌握泛型类的定义与使用,泛型方法的声明与使用,最后感觉了解泛型程序设计及其用途,在验证实验中,通过对代码的解读,更深的学习了泛型程序<T>的使用,还复习了实验九的两个编程题目,感觉依旧存在些小问题,在接下来的实验中要更好的解决,编程实验中,在实验九的四则运算基础上,加入了本章泛型程序的概念,虽然不是很熟练,但还是勉强做出来了。
原文地址:https://www.cnblogs.com/YRQY/p/9891016.html