Help with arrays...Please Help

Question

Hello,
Iam trying to make a library system. I have three classes, one for the GUI, User class, and Users class. User class instantiates an object with all the relevant data like, Name, Age, Address, etc. The Users class contains a array of User Objects.
With this program I have to be able to create users, display users and delete users. The problem Iam having is displaying them. (I think I correctly store the User Objectsin the array, and Iam having problems retreiving them). The thing is when I run the program I don't get any exception errors, just nothing gets displayed!
Here is part of my code:
public class Users {
//declaring variables
public Users (){
initialiseArray();
public void initialiseArray(){
userArray = new User [50];
// This method first checks to see if there is enough room for a new
// user object. If there is the object is added to the array, if there is'nt
// Then method expandUserArray is called to make room for the user
public void addUser( User user)
if (userArraySize == userArray.length) {
expandUserArray();
userArray[userArraySize] = user;
userArraySize++;
// In this method first the user is searched for in the array, if found
// Then method decreaseUserArray is called to delete the user
public void deleteUser ( User user )
location = 0;
while (location < userArraySize && userArray[location] != user) {
location++;
if (userArray[location] == user) {
decreaseUserArray(location);
public void displayUsers( ){
for (int i = 0; i < userArraySize; i++) {
usersInformation += "\n" + (userArray.getUserName());
usersInformation += "\t" + (userArray[i].getUserID());
usersInformation += "\t" + (userArray[i].getUserAddress());
public String getUserInformation(){
//usersInformation = userInformation.toString();
return usersInformation;
// The User is deleted by shifting all the above users one place down
private void decreaseUserArray(int loc)
userArray[loc] = userArray[userArraySize - 1];
userArray[userArraySize - 1] = null;
userArraySize--;
// This method increase the size of the array by 50%
private void expandUserArray( )
int newSize = (int) (userArray.length * increasePercentage);
User newUserArray[] = new User[newSize];
for (int i = 0; i < userArray.length; i++) {
newUserArray[i] = userArray[i];
userArray = newUserArray;
Is there anything wrong with my arrays??? Here is part of my code for action performed:
void addUserButton_actionPerformed(ActionEvent e) {
newUserName = userNameTextField.getText();
newUserAddress = userAdressTextField.getText();
newUserID = Integer.parseInt ( userIDTextField.getText());
User newUser = new User (newUserName, newUserAddress, newUserID);
Users users = new Users();
users.addUser(newUser);
clearButton();
void displayUsersButton_actionPerformed(ActionEvent e) {
Users users = new Users();
users.displayUsers();
displayUsersTextArea.append (users.getUserInformation());
void deleteUserButton_actionPerformed(ActionEvent e) {
//Still incomplete
Thanks for your help!

Answer 1

First, PLEASE USE THE SPECIAL TOKENS FOUND AT
http://forum.java.sun.com/faq.jsp#messageformat WHEN
POSTING CODE!!!! Sorry about that, Iam new and I did'nt know about Special Tokens.
As far as the problem, let me start out by asking if
you've considered using a class that implements the
List interface. Perhaps Vector or ArrayList would
make a better choice since they already handle
"growing" and "shrinking" for you.I tried using vector arrays but it got too complicated. It was very easy to add and remove objects from the vector but I never figured out how to display all the objects with all the data.
public void displayUsers( ){
for (int i = 0; i < userArraySize; i++) {
usersInformation += "\n" +
" + (userArray.getUserName());   //what is
usersInformation?  Also, how does getUserName(),
getUserID(), getUserAddress() know which user object
to operate on if these are methods of userArray?
usersInformation += "\t" +
" + (userArray.getUserID());     //I'm guess you've
only posted "some" of your code. 
usersInformation += "\t" +
" + (userArray.getUserAddress());//Try posting all
that you have so far, and please use the special
tokens to format your code.
}I made a mistake while I was cutting & pasting my code. It should be for example:
usersInformation += "\n" (userArray.getUserName());
The comment about instanciating a new Users for each
actionPerformed is on point. You are replacing your
Usres with a new object each time.Yep this was the problem. I just changed the constructor, declared and
created object of Users elsewhere.
Thanks for your help!