ArrayList adding only last element

Question

below there is a for loop code.I found out by calling a custom display function that the aBook arrayList object only adding last class object thrice. Why is that happening?

Scanner s = new Scanner(System.in);
    ArrayList<LiFiAddressBook> aBook = new ArrayList<LiFiAddressBook>();
    // taking input for every LifIAddressBook and adding them to the ArrayList.
    for (int i = 0; i < 3; i++) {
        System.out.println("Entry " + i+1);
        System.out.print("Please Enter First Name: ");
        String a = s.nextLine();
        System.out.println();
        System.out.print("Please Enter Last Name: ");
        String b = s.nextLine();
        System.out.println();
        System.out.print("Please Enter Street Address: ");
        String c = s.nextLine();
        System.out.println();
        System.out.print("Please Enter City: ");
        String d = s.nextLine();
        System.out.println();
        System.out.print("Please Enter Zip Code: ");
        int e = s.nextInt();
      // in the next line we need to fire a blank scan function in order consume the nextLine. because after executing s.nextInt compiler skip a scan function for a weird reason
        s.nextLine();
        System.out.println();

        LiFiAddressBook x = new LiFiAddressBook(a, b, c, d, e);
        aBook.add(x);


    }

here is my LiFiAddressBook Class

public class LiFiAddressBook {

static  String  first_name, last_name, street_address, city_state;
static int zip_code;

public LiFiAddressBook(String first, String last, String street, String city, int zip) {
  //constructor for class object.
    first_name = first;
    last_name = last;
    street_address = street;
    city_state = city;
    zip_code = zip;
}

public  String get_first() {
    return first_name;
}

public String get_last() {
    return last_name;
}

public String get_address() {
    return street_address;
}

public String get_city() {
    return city_state;
}

public String get_zip() {
    return Integer.toString(zip_code);
}

public static void display() {
    System.out.println("First Name: "+first_name);
    System.out.println("Last Name: "+last_name);
    System.out.println("Street Address"+street_address);
    System.out.println("City State: "+city_state);
    System.out.println("Zip Code: "+zip_code);


}

}

Answer 1

Because of the static keyword, every time the constructor
public LiFiAddressBook(String , String , String , String , int )
is called the old values are over written by the new values and when printed the elements in list the variables of the objects of LiFiAddressBook class points to same objects. hence printing similar objects.

To be clear, actually there are 3 instances of LiFiAddressBook . but the variables/properties of those LiFiAddressBook instances references to same objects.

Answer 2

Remove the static keyword. In essence, that keyword ensures that there is only one instance of those variables.

Answer 3

Make:

static  String  first_name, last_name, street_address, city_state;
static int zip_code;

Into:

String  first_name, last_name, street_address, city_state;
int zip_code;

Also you probably need to change this:

public static void display() {

To:

public void display() {