Java 类的继承基础练习、GregorianCalendar的使用

仍然是课本上的练习题。题目如下：

Y. Daniel Liang:  Introduction to Java Programming 10th, p. 445

 

得到继承层次如图所示：

 

 

• 定义Person类

class Person {
    String name;
    String address;
    String phoneNumber;
    String emailAddress;

    public Person() {
    }

    public Person(String name, String address, String phoneNumber, String emailAddress) {
        this.name = name;
        this.address = address;
        this.phoneNumber = phoneNumber;
        this.emailAddress = emailAddress;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }

    public void setPhoneNumber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    public String getEmailAddress() {
        return emailAddress;
    }

    public void setEmailAddress(String emailAddress) {
        this.emailAddress = emailAddress;
    }

    public String toString() {
        return getName();
    }
}

由于题目要求测试时只返回名字，toString方法并未显示全部信息；其他类也是。

• 定义Student类

class Student extends Person {
    String classStatus;
    public static final String g1 = "freshman";
    public static final String g2 = "sophomore";
    public static final String g3 = "junior";
    public static final String g4 = "senior";

    public Student() {
        classStatus = g1;
    }

    public Student(String classStatus, String name, String address, String phoneNumber, String emailAddress){
        super(name, address, phoneNumber, emailAddress);
        this.classStatus = classStatus;
    }

    public String toString() {
        return "Student: " + super.getName();
    }
}

题目要求的classStatus是常量，这个问题困惑了我很久。在看了这篇博文后有了头绪，并且借鉴了其解法。

• 定义Employee类

class Employee extends Person {
    String office;
    double salary;
    MyDate dateHired;

    Employee() {
        dateHired = new MyDate();
    }

    Employee(String office, double salary, String name, String address, String phoneNumber, String emailAddress) {
        super(name, address, phoneNumber, emailAddress);
        this.office = office;
        this.salary = salary;
        dateHired = new MyDate();
    }

    public String getName() {
        return super.getName();
    }

    public String toString() {
        return "Employee: " + getName();
    }

    /* get Year, month, day respectively*/
    public int getYearHired() {
        return dateHired.getYear();
    }

    public int getMonthHired() {
        return dateHired.getMonth();
    }

    public int getDayHired() {
        return dateHired.getDay();
    }

    //get the date hired and have it printed
    public void getDateHired() {
        System.out.println(getYearHired() + " " + getMonthHired() + " " + getDayHired());
    }

}

---

这里涉及到的MyDate类来自于教材的另一道练习题，题目如下：

Y. Daniel Liang:  Introduction to Java Programming 10th, p. 405

其UML图如下：

MyDate类的UML图

MyDate
year: int month: int day: int date: GregorianCalendarMyDate(long elapsedTime)
+MyDate() +MyDate(elapsedTime: long) +MyDate(year: int, month: int, day: int) +getYear(): int +getMonth(): int +getDay(): int +setDate(elapsedTime: long): void

• 定义MyDate类

//import java.util.GregorianCalendar;
class MyDate{
    int year;
    int month;
    int day;
    GregorianCalendar date = new GregorianCalendar();

    public MyDate(){
        year = date.get(GregorianCalendar.YEAR);
        month = date.get(GregorianCalendar.MONTH);
        day = date.get(GregorianCalendar.DAY_OF_MONTH);
    }

    public MyDate(long elapsedTime) {
        date.setTimeInMillis(elapsedTime);
        year = date.get(GregorianCalendar.YEAR);
        month = date.get(GregorianCalendar.MONTH);
        day = date.get(GregorianCalendar.DAY_OF_MONTH);
    }

    public MyDate(int year, int month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public int getMonth() {
        return month;
    }

    public int getDay() {
        return day;
    }

    public void setDate(long elapsedTime) {
        date.setTimeInMillis(elapsedTime);
    }
}

GregorianCalendar是java.util下的一个类，因此使用时需要先import。

课本对于GregorianCalendar的介绍如下：

Y. Daniel Liang:  Introduction to Java Programming 10th, p. 361

对于本题，这些知识已够用，后面有需要可以再在网上搜索相关介绍及教程。

---

• 定义Faculty类

class Faculty extends Employee {
    String officeHours;
    String rank;

    Faculty() {

    }

    Faculty(String officeHours, String rank, String office, double salary, String name, String address,
            String phoneNumber, String emailAddress) {
        super(office, salary, name, address, phoneNumber, emailAddress);
        this.officeHours = officeHours;
        this.rank = rank;
    }

    public String toString() {
        return "Faculty: " + super.getName();
    }
}

• 定义Staff类

class Staff extends Employee {
    String title;

    Staff() {
    }

    Staff(String title, String office, double salary, String name, String address,
          String phoneNumber, String emailAddress) {
        super(office, salary, name, address, phoneNumber, emailAddress);
        this.title = title;
    }

    public String toString() {
        return "Staff: " + super.getName();
    }
}

其实staff和faculty两个类基本相同，但是通过写这两个，发现自己对于调用父类的父类的方法、super关键字的使用这一方面不太熟悉，等之后有参考答案了再研究一下。

• 测试运行

public class Exercise11_02 {
    public static void main(String[] args) {
        Person person = new Person("张三", "广外", "1111",
                "zs@gdufs.edu.cn");
        System.out.println(person.toString());

        Student student = new Student("g1", "小李", "广外", "2222",
                "xl@gdufs.edu.cn");
        System.out.println(student.toString());

        Employee employee = new Employee("G401", 5005, "大刘", "广外",
                "3333", "dl@gdufs.edu.cn");
        System.out.println(employee.toString());

        Faculty faculty = new Faculty("8-17", "副教授", "A501", 12000, "老王",
                "广外", "4444", "lw@gdufs.edu.cn");
        System.out.println(faculty.toString());

        Staff staff = new Staff("abc", "454", 3003, "王五", "广外",
                "5555", "ww@gdufs.edu.cn");
        System.out.println(staff.toString());
    }
}

只是完成了题目要求的简单测试，后面有时间我会再完善一下toString类型并将测试方法改为从用户输入获取数据。

 

感谢阅读。欢迎批评指正！