我正在努力学习OOP，我有一个有3个班级的程序;人，人事程序（主要）和日期。 Person程序包含新Person的构造函数，包括它们的名字，姓氏，中间名首字母和出生日期。出生日期的类型为Date，而在Date类中，我有一个构造函数，它为生日的日期，月份和年份提供3个整数。我在理解这一切如何协同工作方面遇到了一些麻烦，以及如何正确地调用birthDate。我将使用我的教授为我们设计程序的UML图表。人们的对象就是这样创建的：
people = new Person[5];
people[0] = new Person("Smith", "John", 'T', new Date(4, 2, 1992));
现在我可以理解getter如何为名称和中间名首字母工作。我只是从Person类调用getter并返回所选的。我不明白的是，我在呼唤BirthDate。如果我像其他人一样叫我的生日的吸气剂：
public Date getBirthDate() {
return BirthDate;
}
究竟是什么回归？是否需要调用Date类才能获得某个生日？由于birthdate是用另一个类创建的，它是否会在People对象之外（或内部）创建另一个对象？
我想知道，因为我正在尝试将BirthDate格式化为字符串，因此当用户询问人员信息时，它可以以正确的格式显示。所以在Date类里面我有
public String displayFormattedDate() {
return String.format("%s/%s/%s", String.valueOf(year), String.valueOf(month), String.valueOf(day));
}
那么，我会从Person类中的getter调用它吗？如果是这样我该怎么办？我是否需要在方法内初始化一个新的Date对象才能调用它？
编辑：我的课程代码
人：
public class Person {
private String lastName;
private String firstName;
private char middleInit;
private Date birthDate;
public Person() {}
public Person(String lastName, String firstName, char middleInit, Date birthDate) {
//Person p = new Person("Smith", ... );
setLastName(lastName);
setFirstName(firstName);
setMiddleInit(middleInit);
setBirthDate(birthDate);
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public char getMiddleInit() {
return middleInit;
}
public void setMiddleInit(char middleInit) {
this.middleInit = middleInit;
}
public Date getBirthDate() {
Date birthday = new Date();
return birthDate.displayFormattedDate;
}
public void setBirthDate(Date birthDate) {
this.birthDate = birthDate;
}
public String getFullName() {
return String.format("%s, %s %s.", this.lastName, this.firstName, this.middleInit);
}
}
日期：
public class Date {
private int month;
private int day;
private int year;
public Date(int theMonth, int theDay, int theYear) {
setMonth(theMonth);
setDay(theDay);
setYear(theYear);
}
public int getMonth() {
return month;
}
public int getDay() {
return day;
}
public int getYear() {
return year;
}
public void setMonth(int month) {
if ((month > 0) && (month < 13)) {
this.month = month;
} else {
invalidDate();
}
}
/**
* @param day the day to set
*/
public void setDay(int day) {
int[] days = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
if (month == 2 && day == 29 && (year % 400 == 0
|| (year % 4 == 0 && year % 100 != 0))) {
//day is valid
this.day = day;
} else if (day < 1 || day > days[month]) {
// day is not valid default to 1
day = 1;
this.day = day;
} else {
//day is valid
this.day = day;
}
}
/**
* @param year the year to set
*/
public void setYear(int year) {
this.year = year;
}
public void invalidDate() {
System.out.println("Please input a date number from 1 to 12");
}
public String displayFormattedDate() {
return String.format("%s/%s/%s", String.valueOf(year), String.valueOf(month), String.valueOf(day));
}
}
Personprgraom（主）
import java.util.Scanner;
public class PersonProgram {
Scanner input;
Person[] people;
public PersonProgram() {
input = new Scanner(System.in);
}
public void getData() {
people = new Person[5];
people[0] = new Person("Smith", "John", 'T', new Date(4, 2, 1992));
people[1] = new Person("Terry", "TwoToots", 'G', new Date(9, 14, 1990));
people[2] = new Person("MIke", "Mellow", 'M', new Date(3, 10, 1985));
people[3] = new Person("Steve", "Ramadam", 'N', new Date(4, 20, 1905));
people[4] = new Person("Bizkit", "Limp", 'H', new Date(12, 25, 1972));
}
public int showMenu() {
System.out.println("1. Display all names.");
System.out.println("2. Display info for person by number");
System.out.println("3. Edit information for person by number");
System.out.println("4. Exit");
System.out.println("Choice: ");
int selection = input.nextInt();
return selection;
}
public void executeChoices(int choice) {
switch (choice) {
case 1:
menuOption1();
break;
case 2:
menuOption2();
break;
case 3:
menuOption3();
break;
case 4:
//menuOption4();
}
}
public void menuOption1() {
for (int counter = 0; counter < people.length; counter++) {
System.out.println(counter + 1 + ". " + people[counter].getFullName());
}
}
public void menuOption2() {
System.out.println("Enter person number: ");
int selection = input.nextInt();
System.out.println("Full Name: " + people[selection].getFullName());
System.out.println("Birth Date: " + people[selection].getBirthDate());
}
public void menuOption3() {
System.out.println("Please select a person to edit");
for (int counter = 0; counter < people.length; counter++) {
System.out.println(counter + 1 + ". " + people[counter].getFullName());
}
int choice;
choice = input.nextInt();
System.out.println("What would you like to edit?");
System.out.println("1. First Name");
System.out.println("2. Last Name");
System.out.println("3. Middle initial");
System.out.println("4. Birth Date");
System.out.println("5. Cancel");
int menuselect = input.nextInt();
if (menuselect == 1) {
System.out.println("Enter the new first name: ");
people[choice - 1].setFirstName(input.next());
}
if (menuselect == 2) {
System.out.println("Enter the new last name: ");
people[choice - 1].setLastName(input.next());
}
if (menuselect == 3) {
System.out.println("Enter the new Middle Initial: ");
people[choice - 1].setMiddleInit(input.next().charAt(0));
}
if (menuselect == 4) {
System.out.println("Enter the new birth date: ");
System.out.println("Please enter new Year: ");
int year = input.nextInt();
System.out.println("Please enter new month");
int month = input.nextInt();
System.out.println("Please enter new day");
int day = input.nextInt();
Date birthDate = new Date(month, day, year);
people[choice - 1].setBirthDate(birthDate);
}
if (menuselect == 5) {
System.out.println("Please select a person to edit");
for (int counter = 0; counter < people.length; counter++) {
System.out.println(counter + 1 + ". " + people[counter].getFullName());
}
}
}
public void menuOption4() {
System.exit(0);
}
public static void main(String[] args) {
PersonProgram p = new PersonProgram();
p.getData();
int userinput = p.showMenu();
p.executeChoices(userinput);
}
}
答案 0 :(得分：0)
我认为你会想在Person类中调用toString（）的另一个方法来执行以下操作
public String toString()
{
return (getFullName() + " DOB: " + birthDate.displayFormattedDate());
}
根据您的示例返回一个字符串
"Smith, John T. DOB: 4/2/1992"
答案 1 :(得分：0)
getters 的全部目的是它们返回对象的属性而不做任何更改。因此，getter（通常）不会创建任何类的新实例。 （我通常写＆＃39;因为像其他任何方法一样，getter可以实现，但他们不应该......）
birthDate属性的getter返回通过构造函数传递给对象的对象（在您的示例new Date(4, 2, 1992)中）。
是的，对于显示，您必须使用系统库中的SimpleDateFormat类来为其应用适当的格式。