Checking if an object is in arraylist in Java

Question

So here is assignment :
A student entity has a name and an address (both represented by an object of class Name and Address), in addition to a university ID, and a course schedule represented by an ArrayList of Courses

Your code should not allow the creation of Two students with the same university ID

So I'm thinking of using ArrayList to hold a list of student and check if student exists or not before create a new student. sorry, this is my first question so I'm trying my best to explain it:

This is my Address class:

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);
}

}

This is my Name class

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 +"";
}*/

}

This is my Student class:

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);
 }

}

My question is how can you add Student Object into Student ArrayList and how can I check if the Student Id exists in ArrayList with contains() method

student.contains(id) this line right here it does not seem to be right I hope im explain my question a little clear now. Sorry for my english also.

plz Explain your question properly

abhinavsinghvirsen
– abhinavsinghvirsen

2019-02-25 04:49:10 +00:00
Commented Feb 25, 2019 at 4:49 — abhinavsinghvirsen
– abhinavsinghvirsen, Commented Feb 25, 2019 at 4:49
your question is ambiguous or lack self explanation.

Vishwa Ratna
– Vishwa Ratna

2019-02-25 05:04:27 +00:00
Commented Feb 25, 2019 at 5:04 — Vishwa Ratna
– Vishwa Ratna, Commented Feb 25, 2019 at 5:04

Basil Bourque · Accepted Answer · 2019-02-25 04:52:13Z

1

You would not keep a list of Student objects within the class for Student. Your ArrayList<Student> student=new ArrayList<Student>(); does not belong there.

You would have another structure or collection kept elsewhere named something like StudentBody. When a student is instantiated, it is added to the StudentBody collection.

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

You could loop a List of Student objects in the StudentBody object. For each you would access the UniversityId member field and compare to your new one being added.

Or you could use a Map, where the key is a UniversityId object and the value is a Student object. Check for an existing key before adding.

These solutions ignore the important issue of concurrency. But that is likely okay for a homework assignment in a beginning course in programming.

answered Feb 25, 2019 at 4:52

Basil Bourque

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1 Comment

Meepo Over a year ago

This is the better solution as it avoids making a static field

Syed Khalid Ahmed · Accepted Answer · 2019-02-25 04:53:42Z

Use A HashMap() for collecting information based on unique Ids.

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
    }

}

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