arrayList display method not functioning

[kennith stomps]

Hello Friends, I am having a bit of an issue with my code here, the problem I am attempting to resolve is the listUsers method in the Facebook class (lines 26-29 in the Facebook class  ) If I am to input 1 for a menu choice, I am supposed to run the listUsers method displaying all of the users in my users ArrayList. However, nothing is happening when the listUsers method runs, it simply takes me back to the menu?
Any ideas on what may be causing this issue?

package p1;      // Class A
t 
public abstract class UserAccount {

	private String username;
	private String password;
	private boolean active;

	// no arg constructor
	public UserAccount() {

	}
	// constructor
	public UserAccount(String user, String pass) { // these users are different order than those in constructor sub class
		this.username = user;
		this.password = pass;
		this.active = true;
	}

	public String getUsername() {
		return username;
	}

	public String getPassword() {
		return password;
	}

	public boolean isPasswordCorrect(String pTest) {
		boolean access = false;
		if(this.password == pTest) {
			access = true;
		}
		return access;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public boolean isActive() {
		return active;
	}

	@Override 
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((username == null) ? 0 : username.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		UserAccount other = (UserAccount) obj;
		if (username == null) {
			if (other.username != null)
				return false;
		} else if (!username.equals(other.username))
			return false;
		return true;
	}

	@Override 
	public String toString(){
		String str = this.username;
		return str;

	}
}

package p1;

import java.util.ArrayList;
import java.util.List;

public class FacebookUser extends UserAccount implements Cloneable, Comparable<FacebookUser> {
	
	private String passwordHint;
	private List<FacebookUser> friends = new ArrayList<FacebookUser>();
	
	public FacebookUser() {
		
	}
	
	public FacebookUser(String passHint,
			String user, String pass) {
		super(user, pass);
		
		this.passwordHint = passHint;
	}
	
	public void getPasswordHint(FacebookUser u) {
		System.out.println(this.passwordHint);
	}

	public void setPasswordHint(String hintText) {
		this.passwordHint = hintText;
	}
	
	public void addFriend(FacebookUser friend) throws FacebookException {
		if (friends.contains(friend)) {
			throw new FacebookException("you are alread friends with this person");
		}
		friends.add(friend);
	}
	
	public void removeFriend(FacebookUser friend) throws FacebookException {
		if(friends.contains(friend)) {
			friends.remove(friend);
		}
		else {
			throw new FacebookException("you cannot remove someone who is not your friend");
		}
	}	
	
	public List<FacebookUser> getFriends() {
		return new ArrayList<> (friends);
	}
	
	@Override
	public int compareTo(FacebookUser user) {
		int rc = 0; 
		if (user == null) {
			rc = -1;
		} else {
			String myUserName = getUsername().toLowerCase();
			String otherUserName = user.getUsername().toLowerCase();
			rc = myUserName.compareTo(otherUserName);
		}
		return rc;	
	
		}

	}

package p1;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class Facebook implements Serializable {
	
	 Scanner input = new Scanner(System.in);
	
	private static final String PATH = System.getProperty("user.home") + File.separator + "sinclair" + File.separator;
	private static final String FILE_NAME = "FacebookUsers.dat";
	
	static List<FacebookUser> users;
	
	public Facebook() {
		users = new ArrayList<>();
	}
	// list users method
	protected void listUsers(){
		for(FacebookUser user : users) {
			System.out.println(user.getUsername());
		}
		
	}
	// add user method  
	protected void addUser() {
		System.out.println("please enter user name");	
		input.nextLine();
		String userNameInput = input.nextLine();
		FacebookUser user1 = new FacebookUser("passhint", userNameInput, "password");
		if(users.contains(user1)) {
		System.out.println("Sorry, this user name already exists"); // should I throw an exception here rather than sysout
		return;												
		}
		System.out.println("Enter a password");
		String passwordInput = input.nextLine();
		System.out.println("Enter a password hint");
		String passwordHintInput = input.nextLine();
		FacebookUser newUser = new FacebookUser(passwordHintInput, userNameInput, passwordInput); // is this construction of new FacebookUser good??
		users.add(newUser);             
		}
		
	
	// delete user method
	private void deleteUser() {
		System.out.println("enter the user name you wish to delete");
		input.nextLine();    										// *** I have had to use this because the method would skip my user input. is there a better way to do this? 
		String userToDeleteInput = input.nextLine();
		FacebookUser user1 = new FacebookUser("passHint", userToDeleteInput, "password"); // new facebook user with user name input
		if(!users.contains(user1)) {														// test if user exists in users arrayList, 
		System.out.println("Sorry, the user name you have entered does not exist");				//return to menu if does not exist
		return;
		}
		int idx = users.indexOf(user1);			//  process again gets the actual user
		if(idx<0) {			
			return;									
		}
		FacebookUser user = users.get(idx); // 
		System.out.println("enter " + user1 + "'s password");  // prompt password attempt
		String passwordAttempt = input.nextLine();
		if(!user.isPasswordCorrect(passwordAttempt)){  // this needs fixed
		}
	}
		
	// get password hint method
		private void passwordHint() {
			System.out.println("enter the user name");
			input.nextLine();
			String userToGetHintInput = input.nextLine();
			FacebookUser user1 = new FacebookUser("passHint", userToGetHintInput, "password");
			if(!users.contains(user1)) {
				System.out.println("Sorry, this user does not exist.");
				return;
			}
				int idx = users.indexOf(user1); // get the actual user
				if (idx < 0) {					// returns negative 1 if the user does not exist
					return;						// I don't understand why or how this gets us the actual user
				}								// still needs to be checked when I get the program running***
				FacebookUser user = users.get(idx);
				 user.getPasswordHint(user);		// I think this should work for sysout the passHint***
			}
			
		// quit method
		private void quit() {
			try {
				FileOutputStream fileOut = new FileOutputStream(PATH + FILE_NAME);  
				ObjectOutputStream out = new ObjectOutputStream(fileOut);			
								//if(!PATH.exists()) {
									//? If any of the files do not exist, create them, How do I do this???
								
				out.writeObject(users);
				out.close();
				fileOut.close();
				System.out.println("Data has been serialized");
			} catch(IOException e) {
				e.printStackTrace();
			} finally {
				System.out.println("Goodbye");
			}
			
		}
		
		private void menu() {
			
			int choice = 0;			
			do {
				System.out.println("Menu");
				System.out.println("\t1. List users");
				System.out.println("\t2. Add users");
				System.out.println("\t3. Delete user");
				System.out.println("\t4. Get Password Hint");
				System.out.println("\t5. Quit");
				choice = input.nextInt();
				switch(choice) {
				case 1: 
					listUsers();
					break;
				case 2:
					addUser();
					break;
				case 3: 
					deleteUser();
					break;
				case 4: 
					passwordHint();
					break;
				case 5:
					quit();
					break;
				}
			} while(choice!=5);
		}
		
		public static void main(String[] args) {    //vroom vroom 
			
			Facebook facebook = new Facebook();
			facebook.menu();
		}// end main
}	// end class	

[Prasad Saya]

Hello Friends, I am having a bit of an issue with my code here, the problem I am attempting to resolve is the listUsers method in the Facebook class (lines 26-29 in the Facebook class  ) If I am to input 1 for a menu choice, I am supposed to run the listUsers method displaying all of the users in my users ArrayList. However, nothing is happening when the listUsers method runs, it simply takes me back to the menu? Any ideas on what may be causing this issue?

There was no issue when I run the program. The following code prints the entered users.

    // list users method
    protected void listUsers(){
        for(FacebookUser user : users) {
            System.out.println("# " + user.getUsername());
        }
    }

   

[Ron McLeod]

I would guess that there are no users in your List.  Write a test class to verify your Facebook class is behaving as expected.

public class FacebookTest {
	public static void main(String[] args) {
		listUsersTest();
	}

	private static void listUsersTest() {
		Facebook fb = new Facebook();
		Facebook.users.add(new FacebookUser("banana", "Millie", "secret"));
		Facebook.users.add(new FacebookUser("colley", "Phillippe", "secrète"));

		fb.listUsers();
	}
}

[kennith stomps]

I realize now the list displays so long as I don't exit the program.., I was creating users,  then quitting the program, so that the data would seriialize, however when I start a new program, no users are listed, any idea why this may be ?

[Prasad Saya]

kennith stomps wrote:I realize now the list displays so long as I don't exit the program.., I was creating users,  then quitting the program, so that the data would seriialize, however when I start a new program, no users are listed, any idea why this may be ?

The program needs to save the entered data, and I think it is trying to attempt something like that while a user quits the program (menu option 5). And I see there is an exception then on my pc:

java.io.FileNotFoundException: C:\Users\user1\sinclair\FacebookUsers.dat (The system cannot find the path speci
        at java.io.FileOutputStream.open0(Native Method)
        at java.io.FileOutputStream.open(Unknown Source)
        at java.io.FileOutputStream.<init>(Unknown Source)
        at java.io.FileOutputStream.<init>(Unknown Source)
        at Facebook.quit(Facebook.java:91)
        at Facebook.menu(Facebook.java:133)
        at Facebook.main(Facebook.java:142)

The program need to create the data file and write to it and read from it when needed. The program can do this:
- create a data file when the program starts for the first time.
- write data to the file when new users are entered.
- read the file when the program is started (so that the users are in the memory).

I see some code in the quit() method about writing to a file. But, you need to test that properly  and see if its really doing what it is supposed to do.

[kennith stomps]

I have updated the listUsers method, however it is still not functioning properly after I close the program and re open, no users are listed.

package p1;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class Facebook implements Serializable {
	
	 Scanner input = new Scanner(System.in);
	
	private static final String PATH = System.getProperty("user.home") + File.separator + "sinclair" + File.separator;
	private static final String FILE_NAME = "FacebookUsers.dat";
	
	static List<FacebookUser> users;
	
	public Facebook() {
		users = new ArrayList<>();
	}
	// list users method
	private void listUsers() throws IOException{
		try(
		ObjectInputStream input = new ObjectInputStream(new FileInputStream("FacebookUsers.dat"));
		){
			for(FacebookUser user : users) {
			System.out.println(user.getUsername());
		} 
		}
		
	}
	// add user method  
	protected void addUser()  {
		System.out.println("please enter user name");	
		input.nextLine();
		String userNameInput = input.nextLine();
		FacebookUser user1 = new FacebookUser("passhint", userNameInput, "password");
		if(users.contains(user1)) {
		System.out.println("Sorry, this user name already exists"); // should I throw an exception here rather than sysout
		return;												
		}
		System.out.println("Enter a password");
		String passwordInput = input.nextLine();
		System.out.println("Enter a password hint");
		String passwordHintInput = input.nextLine();
		FacebookUser newUser = new FacebookUser(passwordHintInput, userNameInput, passwordInput); // is this construction of new FacebookUser good??
		users.add(newUser);             
		}
		
	
	// delete user method
	private void deleteUser() {
		System.out.println("enter the user name you wish to delete");
		input.nextLine();    										// *** I have had to use this because the method would skip my user input. is there a better way to do this? 
		String userToDeleteInput = input.nextLine();
		FacebookUser user1 = new FacebookUser("passHint", userToDeleteInput, "password"); // new facebook user with user name input
		if(!users.contains(user1)) {														// test if user exists in users arrayList, 
		System.out.println("Sorry, the user name you have entered does not exist");				//return to menu if does not exist
		return;
		}
		int idx = users.indexOf(user1);			//  process again gets the actual user
		if(idx<0) {			
			return;									
		}
		FacebookUser user = users.get(idx); // 
		System.out.println("enter " + user1 + "'s password");  // prompt password attempt
		String passwordAttempt = input.nextLine();
		if(user.isPasswordCorrect(passwordAttempt)){ 
			users.remove(user);
		}
		if(!users.contains(user)) {								// testing to confirm user has been deleted
			System.out.println("the user has been deleted");
		}
		if(users.contains(user)) {								// testing if user still exists
			System.out.println("something went wrong, " + user.toString() + " still exists."); 
		}
	}
		
	// get password hint method
		private void passwordHint() {
			System.out.println("enter the user name");
			input.nextLine();
			String userToGetHintInput = input.nextLine();
			FacebookUser user1 = new FacebookUser("passHint", userToGetHintInput, "password");
			if(!users.contains(user1)) {
				System.out.println("Sorry, this user does not exist.");
				return;
			}
				int idx = users.indexOf(user1); // get the actual user
				if (idx < 0) {					// returns negative 1 if the user does not exist
					return;						// I don't understand why or how this gets us the actual user
				}								// still needs to be checked when I get the program running***
				FacebookUser user = users.get(idx);
				 user.getPasswordHint(user);		// I think this should work for sysout the passHint***
			}
			
		// quit method
		private void quit() throws IOException, FileNotFoundException {
			try {
				File file = new File("FacebookUsers.dat");
				FileOutputStream fileOut = new FileOutputStream(file);  
				ObjectOutputStream out = new ObjectOutputStream(fileOut);			
				if(!file.exists()) {
					File newFile = new File("FacebookUsers.dat");
				}
								
				for(FacebookUser user: users) {
					out.writeObject(user);
				}
				fileOut.close();
				out.close();
				System.out.println("Data has been serialized");
			}catch (FileNotFoundException e){
				e.printStackTrace();
			}
			finally {
				System.out.println("Goodbye");
			}
		}
		
		
		private void menu() throws FileNotFoundException, IOException {
			
			int choice = 0;			
			do {
				System.out.println("Menu");
				System.out.println("\t1. List users");
				System.out.println("\t2. Add users");
				System.out.println("\t3. Delete user");
				System.out.println("\t4. Get Password Hint");
				System.out.println("\t5. Quit");
				choice = input.nextInt();
				switch(choice) {
				case 1: 
					listUsers();
					break;
				case 2:
					addUser();
					break;
				case 3: 
					deleteUser();
					break;
				case 4: 
					passwordHint();
					break;
				case 5:
					quit();
					break;
				}
			} while(choice!=5);
		}
		
		public static void main(String[] args) throws FileNotFoundException, IOException {    //vroom vroom 
			
			Facebook facebook = new Facebook();
			facebook.menu();
		}// end main
}	// end class	
		
		

[Ron McLeod]

kennith stomps wrote:I have updated the listUsers method, however it is still not functioning properly after I close the program and re open, no users are listed.

Can you explain how storing and retrieving user data works in your application?

[kennith stomps]

The users are added and deleted via the corresponding menu methods,
once the quit method is selected the program then creates a file and object output stream, serializing the data to the facebookUsers.dat file.
Once the program runs again, and I select list users method, the program is to then create an objectInputStream, at which time it reads the arrayList to the console from the facebookUser.dat file
the last process is where I am having the issue
hope this clarifies

[Ron McLeod]

kennith stomps wrote:... Once the program runs again, and I select list users method, the program is to then create an objectInputStream, at which time it reads the arrayList to the console from the facebookUser.dat file

I don't see anywhere in the code that the input stream is being read; also nothing being added to the ArrayList of users.

// list users method
void listUsers() throws IOException {
	try (ObjectInputStream input = new ObjectInputStream(
			new FileInputStream("FacebookUsers.dat"))) {
		for (FacebookUser user : users) {
			System.out.println(user.getUsername());
		}
	}
}

I reformatted the code to make it easier to read

[kennith stomps]

Exactly, that is what I do not know how to do. Do you have any idea how to do this?

[Ron McLeod]

You are on  the right track by creating an ObjectInputStream to deserialize your saved data, but you never actually do anything with it. You will want to:
    - read an object from the stream
    - verify that the object is a FacebookUser type
    - add the user to the list

Also, loading stored users should be separated from displaying the users list.  You don't want to keep adding the saved users to your list each time it is displayed.

For example:

void loadUsers(String filename) {
	int count = 0;
	try (ObjectInputStream input = new ObjectInputStream(
			new FileInputStream(filename))) {
		while (true) {  // don't know how many users were persisted, read until EOF reached
			Object obj = input.readObject();
			if (obj instanceof FacebookUser) {
				FacebookUser user = (FacebookUser) obj;
				users.add(user);
				count++;
			} else {
				System.err.println("File contained unknown type");
			}
		}
	} catch (EOFException e) {
		System.out.println("End of file reached");
	} catch (FileNotFoundException e) {
		System.out.println("File " + filename + " not found");
	} catch (IOException | ClassNotFoundException e) {
		e.printStackTrace();
	}
	System.out.println(count + " users loaded");
}

FacebookUser and UserAccount need to implement Serializable, Facebook doesn't.

I would also rename the quit method to something like saveUsers, since that is what it is actually doing.

Finally, write a simple program to unit test your implementation outside of the full application.  For example:

public class FacebookTest {
	private static final String STORAGE_FILENAME = "d:\\temp\\FacebookUsers.dat";

	public static void main(String[] args) throws IOException {
		saveUsersTest();
		loadUsersTest();
	}

	private static void saveUsersTest() throws IOException {
		Facebook fb = new Facebook();
		Facebook.users.add(new FacebookUser("banana", "Millie", "secret"));
		Facebook.users.add(new FacebookUser("colley", "Phillippe", "secrète"));
		fb.saveUsers();
	}

	private static void loadUsersTest() throws IOException {
		Facebook fb = new Facebook();
		fb.loadUsers(STORAGE_FILENAME);
		fb.listUsers();
	}
}

[kennith stomps]

Here is my solution, thanks for everyones help, the program still has a way to go but it's getting their,

package p1;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.io.Serializable;

public class Facebook implements Serializable {
	
	 Scanner input = new Scanner(System.in);
	
	private static final String PATH = System.getProperty("user.home") + File.separator + File.separator +"Desktop" + File.separator + "Education" + File.separator + "geology" + File.separator + "JAVA II" + File.separator + "StompsNoah_Assignment_03";
	private static final String FILE_NAME = "FacebookUsers.dat";
	
	
	List<FacebookUser> users = new ArrayList();// define users as a List<FacebookUser>
								//*** I do not understand how I would define a field called users,
								// and then define as a list, as the directions said to do. 
							
	 
	public Facebook() {	// why do I have to create this facebook constructor? 
										
		this.users = new ArrayList<>(); // instantiate the list as an array list
	}										// in the constructor.
	private void loadUsers(String path, String fileName)throws ClassNotFoundException {
		try(ObjectInputStream input = new ObjectInputStream(new FileInputStream(path + fileName))) {
//			if(!fileName.exists()) {     ***HOW would I perform this test?? error exists method does not exist
//				new File(PATH).mkdirs();			
//			}
			this.users = (List<FacebookUser>) input.readObject();
		}catch(IOException e) {
			e.printStackTrace();
		}
	}
	// list users method
	private void listUsers(){
		 for(FacebookUser user : this.users) {
	            System.out.println(user.getUsername());
	      }
	}
		
	// add user method  
	protected void addUser()  {
		System.out.println("Please enter a user name, to add to the database");	
		input.nextLine(); // eat what's in the bufffer, i don't  know why this works but it does
		String userNameInput = input.nextLine();
		FacebookUser user1 = new FacebookUser("passhint", userNameInput, "password");
		if(users.contains(user1)) { // if user already exists, prompt error
		System.out.println("Sorry, this user name already exists"); // should I throw an exception here rather than sysout
		return;	// re display the menu										
		}
		System.out.println("Enter a password"); // input password and passwordHint
		String passwordInput = input.nextLine();
		System.out.println("Enter a password hint");
		String passwordHintInput = input.nextLine();
		FacebookUser newUser = new FacebookUser(passwordHintInput, userNameInput, passwordInput); // is this construction of new FacebookUser good??
		this.users.add(newUser);  
		
		}
		
	
	// delete user method
	private void deleteUser() {
		System.out.println("Enter the user name you wish to delete");
		input.nextLine();    	// eat the buffer munch munch yum yum									
		String userToDeleteInput = input.nextLine();
		FacebookUser user1 = new FacebookUser("passHint", userToDeleteInput, "password"); // new facebook user with user name input
		if(!users.contains(user1)) {														// test if user exists in users arrayList, 
		System.out.println("Sorry, the user name you have entered does not exist");				//return to menu if does not exist
		return; 
		}
		int idx = users.indexOf(user1);			//  process again gets the actual user
		if(idx<0) {			
			return;									
		}
		FacebookUser user = users.get(idx); // 
		System.out.println("enter " + user + "'s password");  // prompt password attempt
		String passwordAttempt = input.nextLine();
		if(user.isPasswordCorrect(passwordAttempt)){ 
			users.remove(user);
		} 
		if(!users.contains(user)) {								// testing to confirm user has been deleted
			System.out.println("the user has been deleted");
		}
		if(users.contains(user)) {								// testing if user still exists
			System.out.println("something went wrong, " + user.toString() + " still exists."); 
		}
	}
		
	// get password hint method
		private void passwordHint() {
			System.out.println("enter the user name");
			input.nextLine();
			String userToGetHintInput = input.nextLine();
			FacebookUser user1 = new FacebookUser("passHint", userToGetHintInput, "password");
			if(!users.contains(user1)) {
				System.out.println("Sorry, this user does not exist.");
				return;
			}
				int idx = users.indexOf(user1); // get the actual user
				if (idx < 0) {					// returns negative 1 if the user does not exist
					return;						// I don't understand why or how this gets us the actual user
				}								// still needs to be checked when I get the program running***
				FacebookUser user = users.get(idx);
				 user.getPasswordHint(user);		// I think this should work for sysout the passHint***
			}
			
		// quit method
		private void quit() throws FileNotFoundException {
			
			try {
			
				
				FileOutputStream fileOut = new FileOutputStream(PATH + FILE_NAME);  
				ObjectOutputStream out = new ObjectOutputStream(fileOut);			
				out.writeObject(users);
				System.out.println("Data has been serialized");
			} catch (IOException e) {
				e.printStackTrace();
			}
			finally {
				System.out.println("Goodbye");
			}
		}
		
		
		private void menu() throws FileNotFoundException, IOException, ClassNotFoundException {
			
			int choice = 0;			
			do {
				System.out.println("Menu");
				System.out.println("\t1. List users");
				System.out.println("\t2. Add users");
				System.out.println("\t3. Delete user");
				System.out.println("\t4. Get Password Hint");
				System.out.println("\t5. Quit");
				choice = input.nextInt();
				switch(choice) {
				case 1: 
					listUsers();
					break;
				case 2:
					addUser();
					break;
				case 3: 
					deleteUser();
					break;
				case 4: 
					passwordHint();
					break;
				case 5:
					quit();
					break;
				}
			} while(choice!=5);
		}
		
		public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {    //vroom vroom 
			
			Facebook facebook = new Facebook();	// create a new facebook object, 
			facebook.loadUsers(PATH, FILE_NAME); // load the users arrayList object from FILE_NAME
			facebook.menu();
		}// end main
}	// end class	
		
		
		

[Prasad Saya]

At the start of the application the loadUsers() method throws an exception: java.io.FileNotFoundException:
C:\Users\...\JAVA \StompsNoah_Assignment_03FacebookUsers.dat (The system cannot find the path specified)
       at java.io.FileInputStream.open0(Native Method)
       at java.io.FileInputStream.open(Unknown Source)
       at java.io.FileInputStream.<init>(Unknown Source)
       at java.io.FileInputStream.<init>(Unknown Source)
       at Facebook.loadUsers(Facebook.java:34)
       at Facebook.main(Facebook.java:169)

See this link refers to file related API: https://docs.oracle.com/javase/7/docs/api/java/io/File.html . Here one can find information and file related methods to create a file object and verify if the file exists or not. This may be used to check if the file exists at the program startup and act accordingly.

[Campbell Ritchie]

An alternative would be to use a file chooser. Hint: if you are using a file chooser from the command line, you may need to pass null as the argument to the show XXX dialogue methods.