Question

这是作业：
一个学生实体除具有一个大学ID 之外，还具有一个名称和地址（均由一个 class Name 和 Address 的对象表示），和以课程ArrayList表示的课程表

您的代码不应允许创建两个具有相同大学ID的学生

因此，我正在考虑使用ArrayList来保存学生列表，并在创建新学生之前检查该学生是否存在。抱歉，这是我的第一个问题，所以我正在尽力解释一下：

这是我的地址课程：

public class Address {
private int streetNumber;
private String streetName;
private String city;
private String state;
private int province;
private String country;

public Address (int streetNumber,String streetName,String city,String state,int province,String country)
{
    this.streetNumber=streetNumber;
    this.streetName=streetName;
    this.city=city;
    this.state=state;
    this.province=province;
    this.country=country;
}
public int getStreetNumber() {
    return streetNumber;
}

public void setStreetNumber(int streetNumber) {
    this.streetNumber = streetNumber;
}

public String getStreetName() {
    return streetName;
}

public void setStreetName(String streetName) {
    this.streetName = streetName;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

public String getState() {
    return state;
}

public void setState(String state) {
    this.state = state;
}

public int getProvince() {
    return province;
}

public void setProvince(int province) {
    this.province = province;
}

public String getCountry() {
    return country;
}

public void setCountry(String country) {
    this.country = country;
}

public String toString() {
    return " [streetNumber=" + streetNumber + ", streetName=" + streetName
            + ", city=" + city + ", state=" + state + ", province="+province+", country="
            + country + "]";
}

public boolean equals(Address add)
{
    if(add==null)
    {
        return true;
    }
    if(this.getClass()!=add.getClass())
    {
        return false;
    }
    Address address=(Address) add;
    return streetNumber==address.streetNumber && 
            province==address.province && streetName.equals(address.streetName)
            && city.equals(address.city)&& state.equals(address.state)&& country.equals(address.country);
}

}

这是我的姓名课程

public class Name {
private String firstName;
private String lastName;
private char middle;

public Name (String fiName,String laName, char middle)
{       
    this.firstName=fiName;
    this.lastName=laName;
    this.middle=middle;

}

public String getFirst()
{
    return firstName;
}

public void setFirst(String first)
{
    firstName=first;
}
public String getLast()
{
    return lastName;
}

public void setLast(String last)
{
    lastName=last;
}
public char getMiddle()
{
    return middle;
}
public void setMiddle(char midd)
{
    middle=midd;
}
/*public String toString()
{
     return "[First Name= "+ firstName +" Last Name "+ lastName+" Middle Name "+ middle +"";
}*/

}

这是我的学生班：

public class Student {
private int studentId;
private Name name;
private Address address;
boolean a;
ArrayList<Course> courseSchedule = new ArrayList<Course>();
ArrayList<Student> student=new ArrayList<Student>();

public Student(String fiName,String laName, char middle,int stNumber,String stName,String city,String state,int province,String country,int id)
{
    if(student.contains(id))
    {
        System.out.println("Student cannot be same id");
    }
    else
    {
        address= new Address(stNumber,stName,city,state,province,country);
        name=new Name(fiName,laName,middle);    
        this.studentId=id;
        student.add();
    }

}

public int getID() 
{
    return studentId;
}
public void setId(int id) 
{
    this.studentId = id;
}
public ArrayList<Course> getCourseSchedule() 
{
    return courseSchedule;
}
public void setCourseSchedule(ArrayList<Course> courseSchedule) 
{
    this.courseSchedule = courseSchedule;
}
 public void addCourse(Course c) {
       courseSchedule.add(c);
 }
 public void dropCourse(Course course) {
       courseSchedule.remove(course);
 }

}

我的问题是如何将Student对象添加到Student ArrayList中以及如何使用contains（）方法检查ArrayList中是否存在学生ID

student.contains（id）这行在这里似乎不正确我希望我现在能清楚地解释我的问题。我的英语也很抱歉。

Answer 1

您不会在Student的类中保留Student个对象的列表。您的ArrayList<Student> student=new ArrayList<Student>();不属于那里。

您将在别处保存另一个名为StudentBody的结构或集合。实例化学生后，会将其添加到StudentBody集合中。

List< Student > studentBody = new ArrayList< Student >() ;  // This list is stored somewhere else in your app.

您可以在Student对象中循环List个StudentBody对象。对于每个用户，您都将访问UniversityId成员字段并将其与要添加的新成员进行比较。

或者您可以使用Map，其中key是UniversityId对象，而值是Student对象。添加前检查现有密钥。

这些解决方案忽略了concurrency的重要问题。但这对于编程入门课程中的家庭作业来说可能还可以。

Answer 2

使用HashMap()来基于唯一ID收集信息。

public class Student {
private int studentId;
private Name name;
private Address address;
private static HashMap<Integer,Student> students = new ConcurrentHashMap<>(); // Make a static Map so all objectrs shared same data

public Student(String fiName,String laName, char middle,int stNumber,String stName,String city,String state,int province,String country,int id)
{
    if(students.contains(id))
    {
        System.out.println("Student can be same id");
    }
    else
    {
        address= new Address(stNumber,stName,city,state,province,country);
        name=new Name(fiName,laName,middle);    
        this.studentId=id;
        students.put(id,this);  // use this to add current object
    }

}

Answer 3

通过阅读ArrayList源代码，您应该覆盖学生类的euqals函数。

this

检查对象是否在Java中的arraylist中

3 个答案: