实验六继承定义与使用
实验时间 2018-9-28
一.知识总结
1、继承的概述：在多个类中存在相同的属性和行为，把这些相同的部分抽取到一个单独的类中，把这个单独的类叫作父类，也叫基类或者超类，把其他被抽取的类叫作子类，并且父类的所有属性和方法（除private修饰的私有属性和方法外），子类都可以调用。这样的一种行为就叫做继承。（相同的东西在父类，不同的东西在子类）
2、继承的关键字：extends
3、继承的格式：class 子类名 extends 父类名{ }
4、在代码中使用继承提高了代码的复用性和维护性，让类与类直接产生了关系。
5、继承的注意点：
①子类只能继承父类所有的非私有的成员方法和成员变量，private修饰的不能继承。
②子类不能继承父类的构造方法，但可以通过 super 关键字去访问父类的构造方法。（先初始化父类，再执行自己）
③不同包不能继承。
6、在使用 super 的时候，我们还需要了解关键字 super 和 this 的区别：
super ：到父类中去找方法，没有引用的作用；也可以用于其他方法中；与this调用构造方的重载一样，用于第一行。
this：是指当前正在初始化的这个对象的引用。
二.实验部分：
1、实验目的与要求
(1) 理解继承的定义；
(2) 掌握子类的定义要求
(3) 掌握多态性的概念及用法；
(4) 掌握抽象类的定义及用途；
(5) 掌握类中4个成员访问权限修饰符的用途；
(6) 掌握抽象类的定义方法及用途；
(7)掌握Object类的用途及常用API；
(8) 掌握ArrayList类的定义方法及用法；
(9) 掌握枚举类定义方法及用途。
2、实验内容和步骤
实验1： 导入第5章示例程序，测试并进行代码注释。
测试程序1：
? 在elipse IDE中编辑、调试、运行程序5-1 （教材152页-153页） ；
? 掌握子类的定义及用法；
? 结合程序运行结果，理解并总结OO风格程序构造特点，理解Employee和Manager类的关系子类的用途，并在代码中添加注释。
package inheritance;
import java.time.*;
public class Employee
{
private String name;
private double salary;
private LocalDate hireDay;
//构建三个私有对象
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 inheritance;
public class Manager extends Employee//关键字extends表示继承。表明正在构造一个新类派生于一个已经存在的类。已经存在的类称为超类/基类/或者父类；新类称为子类/派生类/或者孩子类。
{
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); //调用超类中含有n,s,year,month,day参数的构造器
bonus = 0;
}
public double getSalary() //子类要想访问要想访问超类中的方法需要使用特定的关键字super，
{
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double b)
{
bonus = b;
}
}
package inheritance;
/**
* This program demonstrates inheritance.
* @version 1.21 2004-02-21
* @author Cay Horstmann
*/
public class ManagerTest
{
public static void main(String[] args)
{
// 构建管理者对象
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
Employee[] staff = new Employee[3];
// 用管理者和雇员对象填充工作人员数组
staff[0] = boss;
staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
staff[2] = new Employee("Tommy Tester", 40000, 1990, 3, 15);
// 打印所有员工对象的信息
for (Employee e : staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary());
}
}
实验结果：
测试程序2：
? 编辑、编译、调试运行教材PersonTest程序（教材163页-165页)；
? 掌握超类的定义及其使用要求；
? 掌握利用超类扩展子类的要求；
? 在程序中相关代码处添加新知识的注释。
package abstractClasses;
import java.time.*;
public class Employee extends Person
{
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day)
{
super(name);
this.salary = salary;
hireDay = LocalDate.of(year, month, day);
}
public double getSalary()
{
return salary;
}
public LocalDate getHireDay()
{
return hireDay;
}
//重写父类方法，返回一个格式化的字符串
public String getDescription()
{
return String.format("an employee with a salary of $%.2f", salary);
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
}
package abstractClasses;
public abstract class Person
{ //包含一个或多个抽象方法的类被称为抽象类，由abstract关键字修饰
public abstract String getDescription();
private String name;
public Person(String name)
{
this.name = name;
}
public String getName()
{
return name;
}
}
package abstractClasses;
/**
* This program demonstrates abstract classes.
* @version 1.01 2004-02-21
* @author Cay Horstmann
*/
public class PersonTest
{
public static void main(String[] args)
{ //抽象类的声明，但不能将抽象类实例化 ，实例化的是Person类的子类
Person[] people = new Person[2];
// 用学生和雇员填充人物数组
people[0] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
people[1] = new Student("Maria Morris", "computer science");
// 打印所有人对象的名称和描述 for (Person p : people)
System.out.println(p.getName() + ", " + p.getDescription());
}
}
package abstractClasses;
public class Student extends Person
{
private String major;
/**
* @param nama the student‘s name
* @param major the student‘s major
*/
public Student(String name, String major)
{
// 通过n to 总纲构造函数
super(name);
this.major = major;
}
public String getDescription()
{
return "a student majoring in " + major;
}
}
实验结果：
测试程序3：
? 编辑、编译、调试运行教材程序5-8、5-9、5-10，结合程序运行结果理解程序（教材174页-177页）；
? 掌握Object类的定义及用法；
? 在程序中相关代码处添加新知识的注释。
package equals;
import java.time.*;
import java.util.Objects;
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;
}
public boolean equals(Object otherObject)
{
//这里获得一个对象参数，第一个if语句判断两个引用是否是同一个，如果是那么这两个对象肯定相等
if (this == otherObject) return true;
// 如果显式参数为空，则必须返回false
if (otherObject == null) return false;
// if the classes don‘t match, they can‘t be equal
if (getClass() != otherObject.getClass()) return false;
// 现在我们知道另一个对象是非空雇员
Employee other = (Employee) otherObject;
// test whether the fields have identical values
return Objects.equals(name, other.name) && salary == other.salary && Objects.equals(hireDay, other.hireDay);
}
public int hashCode()
{
return Objects.hash(name, salary, hireDay);
}
public String toString()// toString()方法
{
return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay
+ "]";
}
}
package equals;
/**
* This program demonstrates the equals method.
* @version 1.12 2012-01-26
* @author Cay Horstmann
*/
public class EqualsTest
{
public static void main(String[] args)
{
Employee alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee alice2 = alice1;
Employee alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee bob = new Employee("Bob Brandson", 50000, 1989, 10, 1);
System.out.println("alice1 == alice2: " + (alice1 == alice2));
System.out.println("alice1 == alice3: " + (alice1 == alice3));
System.out.println("alice1.equals(alice3): " + alice1.equals(alice3));
System.out.println("alice1.equals(bob): " + alice1.equals(bob));
System.out.println("bob.toString(): " + bob);
Manager carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
System.out.println("boss.toString(): " + boss);
System.out.println("carl.equals(boss): " + carl.equals(boss));
System.out.println("alice1.hashCode(): " + alice1.hashCode());
System.out.println("alice3.hashCode(): " + alice3.hashCode());
System.out.println("bob.hashCode(): " + bob.hashCode());
System.out.println("carl.hashCode(): " + carl.hashCode());
}
}
package equals;
public class Manager extends Employee
{
private double bonus;
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 bonus)
{
this.bonus = bonus;
}
public boolean equals(Object otherObject)
{
if (!super.equals(otherObject)) return false;
Manager other = (Manager) otherObject;
// 检查这个和其他属于同一个类
return bonus == other.bonus;
}
public int hashCode()
{
return java.util.Objects.hash(super.hashCode(), bonus);
}
public String toString()
{
return super.toString() + "[bonus=" + bonus + "]";
}
}
实验结果：
测试程序4：
? 在elipse IDE中调试运行程序5-11（教材182页），结合程序运行结果理解程序；
? 掌握ArrayList类的定义及用法；
? 在程序中相关代码处添加新知识的注释。
package arrayList;
import java.util.*;
/**
* This program demonstrates the ArrayList class.
* @version 1.11 2012-01-26
* @author Cay Horstmann
*/
public class ArrayListTest
{
public static void main(String[] args)
{
// 用三个雇员对象填充工作人员数组列表 ArrayList<Employee> staff = new ArrayList<>();
staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));
staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
staff.add(new Employee("Tony Tester", 40000, 1990, 3, 15));
//把每个人的薪水提高5%
for (Employee e : staff)
e.raiseSalary(5);
// 打印所有员工对象的信息
for (Employee e : staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
+ e.getHireDay());
}
}
package arrayList;
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;
}
}
实验结果：
测试程序5：
? 编辑、编译、调试运行程序5-12（教材189页），结合运行结果理解程序；
? 掌握枚举类的定义及用法；
? 在程序中相关代码处添加新知识的注释。
package enums;
import java.util.*;
/**
* This program demonstrates enumerated types.
* @version 1.0 2004-05-24
* @author Cay Horstmann
*/
public class EnumTest
{
private static Scanner in;
public static void main(String[] args)
{
in = new Scanner(System.in);
System.out.print("Enter a size: (SMALL, MEDIUM, LARGE, EXTRA_LARGE) ");
String input = in.next().toUpperCase();
Size size = Enum.valueOf(Size.class, input);
System.out.println("size=" + size);
System.out.println("abbreviation=" + size.getAbbreviation());
if (size == Size.EXTRA_LARGE)
System.out.println("Good job--you paid attention to the _.");
}
}
enum Size
{
SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");
private Size(String abbreviation) { this.abbreviation = abbreviation; }
public String getAbbreviation() { return abbreviation; }
private String abbreviation;
}
实验结果：
实验2：编程练习1
? 定义抽象类Shape：
属性：不可变常量double PI，值为3.14；
方法：public double getPerimeter()；public double getArea())。
? 让Rectangle与Circle继承自Shape类。
? 编写double sumAllArea方法输出形状数组中的面积和和double sumAllPerimeter方法输出形状数组中的周长和。
? main方法中
1）输入整型值n，然后建立n个不同的形状。如果输入rect，则再输入长和宽。如果输入cir，则再输入半径。
2） 然后输出所有的形状的周长之和，面积之和。并将所有的形状信息以样例的格式输出。
3） 最后输出每个形状的类型与父类型，使用类似shape.getClass()(获得类型)，shape.getClass().getSuperclass()(获得父类型);
思考sumAllArea和sumAllPerimeter方法放在哪个类中更合适？
输入样例:
3
rect
1 1
rect
2 2
cir
1
输出样例:
18.28
8.14
[Rectangle [width=1, length=1], Rectangle [width=2, length=2], Circle [radius=1]]
class Rectangle,class Shape
class Rectangle,class Shape
class Circle,class Shape
package shape;
import java.math.*;
import java.util.*;
import shape.shape;
import shape.Rectangle;
import shape.Circle;
public class shapecount
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
String rect = "rect";
String cir = "cir";
System.out.print("请输入形状个数:");
int n = in.nextInt();
shape[] score = new shape[n];
for(int i=0;i<n;i++)
{
System.out.println("请输入形状类型 (rect or cir):");
String input = in.next();
if(input.equals(rect))
{
double length = in.nextDouble();
double width = in.nextDouble();
System.out.println("Rectangle["+"length:"+length+" width:"+width+"]");
score[i] = new Rectangle(width,length);
}
if(input.equals(cir))
{
double radius = in.nextDouble();
System.out.println("Circle["+"radius:"+radius+"]");
score[i] = new Circle(radius);
}
}
shapecount c = new shapecount();
System.out.println(c.sumAllPerimeter(score));
System.out.println(c.sumAllArea(score));
for(shape s:score)
{
System.out.println(s.getClass()+", "+s.getClass().getSuperclass());
}
}
public double sumAllArea(shape score[])
{
double sum = 0;
for(int i = 0;i<score.length;i++)
sum+= score[i].getArea();
return sum;
}
public double sumAllPerimeter(shape score[])
{
double sum = 0;
for(int i = 0;i<score.length;i++)
sum+= score[i].getPerimeter();
return sum;
}
}
package shape;
public class Rectangle extends shape
{
private double width;
private double length;
public Rectangle(double w,double l)
{
this.width = w;
this.length = l;
}
public double getPerimeter()
{
double Perimeter = (width+length)*2;
return Perimeter;
}
public double getArea()
{
double Area = width*length;
return Area;
}
public String toString()
{
return getClass().getName() + "[ width=" + width + "]"+ "[length=" + length + "]";
}
}
package shape;
public abstract class shape
{
double PI = 3.14;
public abstract double getPerimeter();
public abstract double getArea();
}
package shape;
public class Circle extends shape
{
private double radius;
public Circle(double r)
{
radius = r;
}
public double getPerimeter()
{
double Perimeter = 2*PI*radius;
return Perimeter;
}
public double getArea()
{
double Area = PI*radius*radius;
return Area;
}
public String toString()
{
return getClass().getName() + "[radius=" + radius + "]";
}
}
实验结果：
实验3：编程练习2
编制一个程序，将身份证号.txt 中的信息读入到内存中，输入一个身份证号或姓名，查询显示查询对象的姓名、身份证号、年龄、性别和出生地。
package qq;
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;
public class Test{
private static ArrayList<Citizen> citizenlist;
public static void main(String[] args) {
citizenlist = new ArrayList<>();
Scanner scanner = new Scanner(System.in);
File file = new File("D:\\身份证号.txt");
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 address =linescanner.nextLine();
Citizen citizen = new Citizen();
citizen.setName(name);
citizen.setId(id);
citizen.setSex(sex);
citizen.setAge(age);
citizen.setAddress(address);
citizenlist.add(citizen);
}
} catch (FileNotFoundException e) {
System.out.println("信息文件找不到");
e.printStackTrace();
} catch (IOException e) {
System.out.println("信息文件读取错误");
e.printStackTrace();
}
boolean isTrue = true;
while (isTrue) {
System.out.println("1.按姓名查询");
System.out.println("2.按身份证号查询");
System.out.println("3.退出");
int nextInt = scanner.nextInt();
switch (nextInt) {
case 1:
System.out.println("请输入姓名");
String citizenname = scanner.next();
int nameint = findCitizenByname(citizenname);
if (nameint != -1) {
System.out.println("查找信息为：身份证号:"
+ citizenlist.get(nameint).getId() + " 姓名:"
+ citizenlist.get(nameint).getName() +" 性别:"
+citizenlist.get(nameint).getSex() +" 年龄:"
+citizenlist.get(nameint).getAge()+" 地址:"
+citizenlist.get(nameint).getAddress()
);
} else {
System.out.println("不存在该公民");
}
break;
case 2:
System.out.println("请输入身份证号");
String citizenid = scanner.next();
int idint = findCitizenByid(citizenid);
if (idint != -1) {
System.out.println("查找信息为：身份证号:"
+ citizenlist.get(idint ).getId() + " 姓名:"
+ citizenlist.get(idint ).getName() +" 性别:"
+citizenlist.get(idint ).getSex() +" 年龄:"
+citizenlist.get(idint ).getAge()+" 地址:"
+citizenlist.get(idint ).getAddress()
);
} else {
System.out.println("不存在该公民");
}
break;
case 3:
isTrue = false;
System.out.println("程序已退出!");
break;
default:
System.out.println("输入有误");
}
}
}
public static int findCitizenByname(String name) {
int flag = -1;
int a[];
for (int i = 0; i < citizenlist.size(); i++) {
if (citizenlist.get(i).getName().equals(name)) {
flag= i;
}
}
return flag;
}
public static int findCitizenByid(String id) {
int flag = -1;
for (int i = 0; i < citizenlist.size(); i++) {
if (citizenlist.get(i).getId().equals(id)) {
flag = i;
}
}
return flag;
}
}
package qq;
public class Citizen {
private String name;
private String id ;
private String sex ;
private String age;
private String address;
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 String getSex() {
return sex ;
}
public void setSex(String sex ) {
this.sex =sex ;
}
public String getAge() {
return age;
}
public void setAge(String age ) {
this.age=age ;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address=address ;
}
}
实验结果：
实验总结：
上周我们学习了第五章，这章中主要学了继承这一概念，通过继承人们可以在已存在的类构造一个新类，继承已存在的类就是复用这些类的方法和域，通过继承这一概念我们学习了一些类的概念如：超类，基类（父类），子类等。总的来说本章的知识点也是比较重要的，不过我对本章的知识掌握的不是很好，我会继续努力的，多多敲代码。
原文地址：https://www.cnblogs.com/D980321/p/9739816.html
时间： 2024-08-29 14:45:10