项目 |
内容 |
《面向对象程序设计(java)》 |
https://www.cnblogs.com/nwnu-daizh/ |
这个作业的要求在哪里 |
https://www.cnblogs.com/nwnu-daizh/p/11815810.html |
作业学习目标 |
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第一部分:总结第八章关于泛型程序设计理论知识。
1.泛型:何为泛型,就是参数化类型,在定义类、接口、方法时通过类型参数指示将要处理的对象类型
2.泛型程序设计意味着编写的代码可以被许多不同类型的对象所重用
3.定义简单泛型类:
(1)一个泛型类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
(2)以Pair类为例:public class Pair<T>
{
......
}
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
(3)泛型类可以有多个类型变量。例如,可以定义Pair类,其中第一个域和第二个域使用不同的类型:public class Pair<T,U> { ... }
(4)类定义中的类型变量指定方法的返回类型以及域和局部变量的类型
(5)实例化泛型对象时,一定要在类名后面指定类型参数的值,一共要有两次书写,例如:TestGeneric<String,String> t=new TestGeneric<String,String>();
4.泛型方法:
(1)定义泛型方法时注意,类型变量放在修饰符(public static)的后面,返回类型的前面
(2)泛型方法可以定义在普通类中,也可以定义在泛型类中
(3)当调用一个泛型方法时,在方法名前的尖括号中放入具体的类型
5.泛型接口的定义与实现:
(1)定义:public interface IPool<T>
{
T get();
int add(T t);
}
(2)实现:public class GenericPool<T> implements IPool<T> { ... }
public class GenericPool implements IPool<Account> { ... }
6.类型变量的限定:
(1)定义泛型变量的上界(用extends)
<T extends BoundingType>表示T是绑定类型的子类型。T和绑定类型可以是类,也可以是接口
一个类型变量或通配符可以有多个限定,例如:T extends Comparable & Serializable(限定类型用“&”分隔)
(2)定义泛型变量的下界(用super) 例如:<? super T>
7.泛型类的约束与局限:
(1)不能用基本类型实例化类型参数
(2)运行时类型查询只适用于原始类型
(3)不能抛出也不能捕获泛型类实例
(4)参数化类型的数组不合法
(5)不能实例化类型变量
(6)泛型类的静态上下文中类型变量无效
(7)注意擦除后的冲突
8.泛型类型的继承规则:Java中的数组是协变的,但泛型类不是协变的
9.通配符类型:(?,任何类型;T,某一种类型)
(1)单独的?,用于表示任何类型
(2)?extends type,表示带有上界
(3)? super type,表示带有下界
10.(1)通配符的类型限定: Pair<? extends Employee>
Pair<? super Manager>
(2)无限定通配符:Pair<?>(Pair<?>与Pair的不同在于:可以用任意Object对象调用原始的Pair类的setObject方法)
第二部分:实验部分
实验1:测试程序1
运行代码:
PairTest1:
public class PairTest1 { 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 { /** * Gets the minimum and maximum of an array of strings. * @param a an array of strings * @return a pair with the min and max values, or null if a is null or empty */ public static Pair<String> minmax(String[] a)//改主类是String形的。 { 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);//该处<>中省略的是String。 } }
pair:
public class Pair<T> //用到了泛型技术。 { 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;}
}
运行结果如下:
实验1:测试程序2
运行代码如下:
PairTest2:
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);//该处用到了泛型技术 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 values, or null if a is null or empty */ public static <T extends Comparable> Pair<T> minmax(T[] a) //该处用到了泛型技术 { 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);//<>里面省略了T。 } }
pair:
public class Pair<T> //泛型技术 { 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; } }
运行结果;
实验1:测试程序1
PairTest3:
public class PairTest3 { public static void main(String[] args) { var ceo = new Manager("Gus Greedy", 800000, 2003, 12, 15); var cfo = new Manager("Sid Sneaky", 600000, 2003, 12, 15); var buddies = new Pair<Manager>(ceo, cfo); printBuddies(buddies); ceo.setBonus(1000000); cfo.setBonus(500000); Manager[] managers = { ceo, cfo }; var result = new Pair<Employee>(); 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); } }
pair:
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; } }
Manager:
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; } }
Employee:
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; } }
运行结果:
实验2:结对编程练习
运行代码:
package tuxing; import java.util.ArrayList; import java.util.Scanner; interface GeneralStack<T> { public T push(T item); //如item为null,则不入栈直接返回null。 public T pop(); //出栈,如为栈为空,则返回null。 public T peek(); //获得栈顶元素,如为空,则返回null. public boolean empty(); //如为空返回true public int size(); //返回栈中元素数量 } class ArrayListGeneralStack implements GeneralStack { ArrayList list = new ArrayList(); public String toString() { return list.toString(); } @Override public Object push(Object item) { if (list.add(item)){ return item; }else { return false; } } @Override public Object pop() { if (list.size()==0){ return null;} return list.remove(list.size()-1); } @Override public Object peek() { if(list.size()!=0) return list.get(list.size()-1); return null; } @Override public boolean empty() { if(list.size()==0) return true; return false; } @Override public int size() { // TODO Auto-generated method stub return list.size(); } } class Car { private int id; private String name; @Override public String toString() { return "Car [" + "id=" + id +", name=" + getName() +']'; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Car(int id, String name) { this.id = id; this.setName(name); } } public class Main { public static void main(String[] args) { Scanner in = new Scanner(System.in); while(true){ String c = in.nextLine(); if(c.equals("Integer")) { System.out.println("Integer Test"); int m=in.nextInt(); int n=in.nextInt(); ArrayListGeneralStack array = new ArrayListGeneralStack(); for(int i=0;i<m;i++) { System.out.println("push:"+array.push(in.nextInt())); } for(int i=0;i<n;i++) { System.out.println("pop:"+array.pop()); } System.out.println(array.toString()); int sum=0; int size=array.size(); for(int i=0;i<size;i++) { sum+=(int)array.pop(); } System.out.println("sum="+sum); System.out.println("interface GeneralStack"); } else if(c.equals("Double")) { System.out.println("Double Test"); int m = in.nextInt(); int n = in.nextInt(); ArrayListGeneralStack array = new ArrayListGeneralStack(); for (int i=0;i<m;i++) { System.out.println("push:"+array.push(in.nextDouble())); } for(int i=0;i<n;i++) { System.out.println("pop:"+array.pop()); } System.out.println(array.toString()); double sum=0; int size=array.size(); for(int i =0;i<size;i++) { sum+=(double)array.pop(); } System.out.println("sum="+sum); System.out.println("interface GeneralStack"); } else if(c.equals("Car")) { System.out.println("Cat Test"); int m=in.nextInt(); int n=in.nextInt(); ArrayListGeneralStack array = new ArrayListGeneralStack(); for(int i=0;i<m;i++) { int id = in.nextInt(); String name = in.next(); Car car = new Car(id, name); System.out.println("push"+array.push(car)); } for(int i =0;i<n;i++) { System.out.println("pop"+array.pop()); } System.out.println(array.toString()); int size=array.size(); for(int i=0;i<size;i++) { Car car=(Car) array.pop(); System.out.println(car.getName()); } System.out.println("interface GeneralStack"); } else if (c.equals("quit")){ System.exit(0);; }} } }
运行结果:
实验总结:
通过本周的学习,我了解到了java中的泛型技术,其中包括了泛型概念;泛型类的定义与使用;泛型方法的声明与使用;泛型接口的定义与实现;泛型程序设计,理解其用途等。其中的概念部分理解起来还算可以,但是一到编写程序,愣是趴在电脑旁一个字都敲不上去,说不会吧,可就在上节课学长的演示下我觉的我的思路很清晰,一会儿就能把代码搞出来,回到宿舍自己一搞,哇,全乱套了,敲一行删两行,我太难了,从现在开始我一定要好好学习天天向上。