Java - Loop through instances of a class

[Kevin O'Sullivan]

I have 3 instances of a book class, two hard coded and one that will book to a list via user input, What is the best way to iterate through different instances of a class

public void enterBookDetails(){
        while(true){
            System.out.println("Please enter name of book: ");
            String bookName = UserInput.scan.next();

            if(bookName.equalsIgnoreCase("end")){
                break;
            }

            System.out.println("Please enter author name: ");
            String authorName = UserInput.scan.next();

            System.out.println("Please enter number of copies: ");
            int numberOfCopiesInStock = UserInput.checkInput();

            System.out.println("Please enter ISBN number: ");
            String ISBN = UserInput.scan.next();


          
               Book book1 = new Book("American Gods","Neil Gaimen",2,"A1233454346765456");
               Book book2 = new Book("NeverWhere","Neild Gaimen",1,"A1334567654376787");
               Book book3 = new Book(bookName,authorName,numberOfCopiesInStock,ISBN);
               UserInput.book.add(book1);
               UserInput.book.add(book2);
               UserInput.book.add(book3);
              
           
           }
        }
    }

[Carey Brown]

Use an enhanced for() loop.

for( Book b : UserInput.book ) { ... }

[Carey Brown]

It's not clear why UserInput has-a collection of Books.

[Carey Brown]

The use of scan.next() on lines 4, 11, and 17 should probably be replaced by scan.nextLine(). You want to be able to include spaces and you want to capture every thing type until the Enter key is pressed. In the case of ISBN you may need additional logic to reject ill formed ISBN numbers.

On line 14 you have an int that receives its value from checkInput(). The name "checkInput()" does not describe the kind of task that we expect an int back from. A better name should be used that describes what the method does.

Lines  24 and 25 are going to be called each time around the while() loop, thus adding the books from lines 21 and 22 multiple times. What will your code do if the same Book is entered more than once?

[Paul Clapham]

Carey Brown wrote:It's not clear why UserInput has-a collection of Books.

Nor why this collection of Books is named "book".

[Campbell Ritchie]

Carey Brown wrote:The use of scan.next() on lines 4, 11, and 17 should probably be replaced by scan.nextLine(). . . .

Agree; there is however a problem. It is likely that the call in line 17 is preceded by nextInt(). In which case there is a risk of nextLine() returning an empty String. If this happens, your inputs will be thrown out of sequence; there is more explanation and a possible solution in this old post. Creating an input utility class would be a much more time‑consuming solution, but I prefer it. Such a class would allow you not to write multiple dot operators (see line 11).

. . . additional logic to reject ill formed ISBN numbers.

The ISBNs shown are indeed ill‑formed. It would be better to create an ISBN class and make it immutable and do the validation in its constructor than to try using plain Strings.

[Kevin O'Sullivan]

Thanks for replies, I was trying to spilt everything into classes, I'll just post all the code up, maybe ye can give me some pointers, just on the nextline thing carey mentioned , I was having trouble with that in that it would skip the next line so changed it to next(); and that worked but I make any spaces then then I tried putting next(); after it and that didn't work either, also how come it won't let me print out the list of books hardcoded into but If insert one book in via user input and then choose display all book option it will display them all ?

import java.util.*;
public class UserInput {

    private static Random random = new Random();
    public static final Scanner scan = new Scanner(System.in);
    public static boolean keepGoing = true;
    public static ArrayList<Book>book = new ArrayList<Book>();

    private static final String ERROR_MESSAGE = "INVALID OPTION SELECTED!";
    private static final String BAD_INPUT = "INVALID INPUT! NUMBER ONLY! ";

    public static void welcomeMessage(){
        System.out.println("********************");
        System.out.println("*	  Welcome To   *");
        System.out.println("*	 Cork Library  *");
        System.out.println("********************");
    }

    public static void menuHeader(){
        System.out.println("********************");
        System.out.println("*		Menu	   *");
        System.out.println("*      Options     *");
        System.out.println("********************");
    }

    public static void menuOptions(){
        System.out.println("1.) Add Book.	         ");
        System.out.println("2.) Search for Book.  	 ");
        System.out.println("3.) Delete Book.      	 ");
        System.out.println("4.) Display all Books.   ");
        System.out.println("5.)");
        System.out.println("0.) Exit.                ");
        System.out.println("*************************");
    }

    public static void getUserInput(){
        int choice;
        menuHeader();
        do{
            menuOptions();
            System.out.print(">");
            choice = checkInput();
            pickOption(choice);
        }while(choice != 0);
    }

    private static void pickOption(int choice){
        switch(choice){
            case 1: AddBook addBook = new AddBook();
                    addBook.enterBookDetails();
                break;

            case 2:
                break;

            case 3:
                break;

            case 4: AddBook a = new AddBook();
                    a.print();
                break;

            case 5:
                break;

            case 0: Exit e = new Exit();
                    e.exitMessage();
                break;

            default:
                System.out.println(ERROR_MESSAGE);
                break;
        }
    }




    private static void run(){
        int number = random.nextInt(10)+1;
        System.out.println("Check system......please wait....");
        try{
            Thread.sleep(number * 1000);
        }catch(InterruptedException e){
            e.printStackTrace();
        }
    }

    public static int checkInput(){
        while(keepGoing){
            try{
                return scan.nextInt();
            }catch(InputMismatchException w){
                scan.next();
                System.err.print(BAD_INPUT);
            }
        }
        return scan.nextInt();
    }

}

public class Book implements ILibrary{
    private String bookName;
    private String authorName;
    private int numberOfCopiesInStock;
    private String ISBN;

    //Constructor
    public Book(String bookName,String authorName,int numberOfCopiesInStock,String ISBN){
        this.bookName = bookName;
        this.authorName = authorName;
        this.setNumberOfCopiesInStock(numberOfCopiesInStock);
        this.setISBN(ISBN);
    }

    //Setters
    public void setNumberOfCopiesInStock(int numberOfCopiesInStock)throws IllegalArgumentException{
        if(numberOfCopiesInStock < MIN_NUMBER_OF_COPIES || numberOfCopiesInStock > MAX_NUMBER_OF_COPIES){
            throw new IllegalArgumentException();
        }else{
            this.numberOfCopiesInStock = numberOfCopiesInStock;
        }
    }

    public void setISBN(String ISBN)throws IllegalArgumentException{
        if(ISBN.length() < ISBN_MAX_OF_DIGITS || ISBN.length() > ISBN_MAX_OF_DIGITS){
            throw new IllegalArgumentException();
        }else{
            this.ISBN = ISBN;
        }
    }

    //Getters
    public String getBookName(){
        return this.bookName;
    }

    public String getAuthorName(){
        return this.authorName;
    }

    public int getNumberOfCopiesInStock(){
        return this.numberOfCopiesInStock;
    }

    public String getISBN(){
        return this.ISBN;
    }

    //ToString method
    public String toString(){
        return("BookName: " + getBookName()
                +"\n"
                +"AuthorName: " + getAuthorName()
                +"\n"
                +"Number of Copies: " + getNumberOfCopiesInStock()
                +"\n"
                +"ISBN: " + getISBN());
    }

}

public interface ILibrary {

    int MAX_NUMBER_OF_COPIES = 2;
    int MIN_NUMBER_OF_COPIES = 0;
    int ISBN_MAX_OF_DIGITS = 17;

}

[Norm Radder]

Can you copy the contents of the command prompt window that shows the problems you are talking about?
Be sure to add some comments to the output to show where the output wasn't expected.
For example:
 <<<< This should be ....

[Kevin O'Sullivan]

Norm Radder wrote:Can you copy the contents of the command prompt window that shows the problems you are talking about?
Be sure to add some comments to the output to show where the output wasn't expected.
For example:
 <<<< This should be ....

No problem I'll do it tomorrow as it bedtime now .

[Carey Brown]

"AddBook" is a verb phrase, it describes an action not an object. Objects have data and behaviors. A library has Books (data) and can add-a-book (behavior). Your UserInput class has some static methods that would be appropriate for a utility class but as such it should not have knowledge of how it's being used by the next layer up. For instance, if you have a Library class with Books that may make several calls to your UserInput class, such as getMenuChoice(). In UserInput the getMenuChoice() method should not know or care about how the choice value to be returned is to be used. So the switch() more rightly belongs in the Library layer.

See my signature below, it has a link to a KeyboardUtility class. You could use it as is, copy it and hack away at it till it has only what you need, or get some ideas from it (or ignore it). The problem you mentioned about missing inputs when you changed to nextLine() is addressed in that wrapper class.

The long explanation of your missing data problem is that nextInt() will leave a new-line pending in the input queue. Then when you call nextLine() the first thing it sees is the new-line and thinks that the input is complete resulting in an empty string. There are two ways to fix this: 1) don't use nextInt(), use nextLine() for everything (this is the way my utility was written), or 2) flush the new-line after nextInt() by a separate call to nextLine() that just throws the empty string away. Example:

int i1 = scan.nextInt();
scan.nextLine(); // flush new-line
String name = scan.nextLine();

This holds true for all the nextXXX() methods except nextLine().

[Carey Brown]

public class Library {
    private List<Book> books = new ArrayList<>(); // proper way to write this. "books" plural.

[Campbell Ritchie]

I used to handle nextLine() like that but since I wrote my utility class I have taken a different approach, with a loop, something like this:-

public static String nextLine(String message)
{
   System.out.println(message)
   String line;
   while ((line = myScanner.nextLine().strip()).isEmpty());
   return line;
}

The message parameter would be something like, “Please enter address: ”. I took great delight in writing a while with a semicolon at the end because everybody knows you aren't supposed to do that
It keeps repeating until a non‑empty line is found. The strip() method was intoduced about Java11 to remove leading and trailing whitespace; I prefer it to trim(). A Scanner allows you to anticipate an input: in this sort of interaction (user input underlined), nextInt()...nextLine() will interpret the input correctly:-

Enter number of toes:
93 742 Evergreen Terrace Springield
Enter address please:

Maybe I have very big feet./* alternative version with more conventional loop */ public static String nextLine(String message) {   System.out.println(message)   String line   do   {      line = myScanner.nextLine().strip());   } while (line.isEmpty());   return line; }

[Kevin O'Sullivan]

Thanks for all the replies, very helpful as always.

I have two books hardcoded into the library how come it won't print out that list of 2 books when I call the print() menthod ? but for some reason I have use the userinput to input one book and then it will display all 3 books, any ideas?

try{
                Book book3 = new Book(bookName,authorName,numberOfCopiesInStock,ISBN);
                Book book1 = new Book("American Gods","Neil Gaimen",2,"A1233454346765456");
                Book book2 = new Book("NeverWhere","Neild Gaimen",1,"A1334567654376787");
                UserInput.book.add(book3);
                UserInput.book.add(book1);
                UserInput.book.add(book2);


            }catch(Exception e){
                e.printStackTrace();
            }
        }
    }

    public void print(){
        for(Book b:UserInput.book){
            System.out.println(b.toString());
            System.out.println();
        }

    }

Here is the command prompt, when I press 4 a list of books should appear but as you can see nothing is showing

********************
*	  Welcome To   *
*	 Cork Library  *
********************
********************
*		Menu	   *
*      Options     *
********************
1.) Add Book.	         
2.) Search for Book.  	 
3.) Delete Book.      	 
4.) Display all Books.   
5.)                      
0.) Exit.                
*************************
>4
1.) Add Book.	         
2.) Search for Book.  	 
3.) Delete Book.      	 
4.) Display all Books.   
5.)                      
0.) Exit.                
*************************
>

[Norm Radder]

Is there anything to print in the new instance of the AddBook class's print method?
Add a print statement to the print() method that prints out the size of the list that is to be printed.

[Campbell Ritchie]

Also, please go through the case 4: code carefully and see what it actually does.

[Kevin O'Sullivan]

Norm Radder wrote:Is there anything to print in the new instance of the AddBook class's print method?
Add a print statement to the print() method that prints out the size of the list that is to be printed.

public void print(){
        for(Book b:UserInput.book){
            System.out.println(b.toString());
            System.out.println(UserInput.book.size());
        }

Something like the above? it still didn't print anything.

[Carey Brown]

I'm guessing that this print method isn't even being called because it's not a method inside AddBook class.

[Norm Radder]

 it still didn't print anything.

If the list is empty, the loop won't iterate.  If the loop doesn't execute, the print statement won't be executed.  But you already knew that because nothing was printed.
Move it outside of the loop.

[Kevin O'Sullivan]

Carey Brown wrote:I'm guessing that this print method isn't even being called because it's not a method inside AddBook class.

No it is in the AddBook class

public void enterBookDetails(){
        while(true){

            System.out.println("Please enter number of copies: ");
            int numberOfCopiesInStock = UserInput.checkInput();
            UserInput.scan.nextLine();

            if(numberOfCopiesInStock == 0){
                break;
            }

            System.out.println("Please enter name of book: ");
            String bookName = UserInput.scan.nextLine();

            System.out.println("Please enter author name: ");
            String authorName = UserInput.scan.nextLine();

            System.out.println("Please enter ISBN number: ");
            String ISBN = UserInput.scan.nextLine();


            try{
                Book book3 = new Book(bookName,authorName,numberOfCopiesInStock,ISBN);
                Book book1 = new Book("American Gods","Neil Gaimen",2,"A1233454346765456");
                Book book2 = new Book("NeverWhere","Neild Gaimen",1,"A1334567654376787");
                UserInput.book.add(book3);
                UserInput.book.add(book1);
                UserInput.book.add(book2);


            }catch(Exception e){
                e.printStackTrace();
            }
        }
    }

    public void print(){
        for(Book b:UserInput.book){
            System.out.println(b.toString());

        }
        System.out.println(UserInput.book.size());

    }


}

[Kevin O'Sullivan]

Norm Radder wrote:

 it still didn't print anything.

If the list is empty, the loop won't iterate.  If the loop doesn't execute, the print statement won't be executed.  But you already knew that because nothing was printed.
Move it outside of the loop.

Ok I see what you mean now, it printed zero which tells me the hardcoded books aren't even added to the list.

[Norm Radder]

books aren't even added to the list.

A first step.
Where are the books supposed to be added?  Why isn't that code being executed?

[Kevin O'Sullivan]

Norm Radder wrote:

books aren't even added to the list.

A first step.
Where are the books supposed to be added?  Why isn't that code being executed?

Suppose to be added to the Book list in the UserInput class, I can't figure out why there not being added though, seeing as there being as added when prompted too .

[Carey Brown]

Could you please re-post ALL of the code again. I think the problem lies somewhere other than the snippets we're seeing.

[Norm Radder]

Suppose to be added

Is that code being executed?  Add a print statement so you can see.

[Kevin O'Sullivan]

Carey Brown wrote:Could you please re-post ALL of the code again. I think the problem lies somewhere other than the snippets we're seeing.

Sure thing, thanks for your help.

public class Main {

    public static void main(String[] args) {
        UserInput.welcomeMessage();
        UserInput.getUserInput();
	
    }
}

import java.util.*;
public class UserInput {

    private static Random random = new Random();
    public static final Scanner scan = new Scanner(System.in);
    public static boolean keepGoing = true;
    public static ArrayList<Book>book = new ArrayList<Book>();

    private static final String ERROR_MESSAGE = "INVALID OPTION SELECTED!";
    private static final String BAD_INPUT = "INVALID INPUT! NUMBER ONLY! ";

    public static void welcomeMessage(){
        System.out.println("********************");
        System.out.println("*	  Welcome To   *");
        System.out.println("*	 Cork Library  *");
        System.out.println("********************");
    }

    public static void menuHeader(){
        System.out.println("********************");
        System.out.println("*		Menu	   *");
        System.out.println("*      Options     *");
        System.out.println("********************");
    }

    public static void menuOptions(){
        System.out.println("1.) Add Book.	         ");
        System.out.println("2.) Search for Book.  	 ");
        System.out.println("3.) Delete Book.      	 ");
        System.out.println("4.) Display all Books.   ");
        System.out.println("5.)                      ");
        System.out.println("0.) Exit.                ");
        System.out.println("*************************");
    }

    public static void getUserInput(){
        int choice;
        menuHeader();
        do{
            menuOptions();
            System.out.print(">");
            choice = checkInput();
            pickOption(choice);
        }while(choice != 0);
    }

    private static void pickOption(int choice){
        switch(choice){
            case 1: AddBook addBook = new AddBook();
                    addBook.enterBookDetails();
                break;

            case 2: 
                Search s = new Search();
                s.search();
                break;

            case 3:
                break;

            case 4: AddBook a = new AddBook();
                    a.print();
                break;

            case 5:
                break;

            case 0: Exit e = new Exit();
                    e.exitMessage();
                break;

            default:
                System.out.println(ERROR_MESSAGE);
                break;
        }
    }




    public static void run(){
        int number = random.nextInt(10)+1;
        System.out.println("Check system......please wait....");
        try{
            Thread.sleep(number * 1000);
        }catch(InterruptedException e){
            e.printStackTrace();
        }
    }

    public static int checkInput(){
        while(keepGoing){
            try{
                return scan.nextInt();
            }catch(InputMismatchException w){
                scan.next();
                System.err.print(BAD_INPUT);
            }
        }
        return scan.nextInt();
    }




}

public class Search {

    public boolean search(){
        System.out.println("\n**********Search Book**********");
        System.out.println("Please enter name of book: ");
        String bookName = UserInput.scan.next();
        //UserInput.scan.next();
        UserInput.run();
        for(Book i : UserInput.book){
            if(i.getBookName().equalsIgnoreCase(bookName)){
                System.out.println(i);
                return true;
            }
        }
        System.out.println("BOOK NOT FOUND! ");
        return false;
    }
}

public class AddBook {

    public void enterBookDetails(){
        while(true){

            System.out.println("Please enter number of copies: ");
            int numberOfCopiesInStock = UserInput.checkInput();
            UserInput.scan.nextLine();

            if(numberOfCopiesInStock == 0){
                break;
            }

            System.out.println("Please enter name of book: ");
            String bookName = UserInput.scan.nextLine();

            System.out.println("Please enter author name: ");
            String authorName = UserInput.scan.nextLine();

            System.out.println("Please enter ISBN number: ");
            String ISBN = UserInput.scan.nextLine();


            try{
                Book book3 = new Book(bookName,authorName,numberOfCopiesInStock,ISBN);
                Book book1 = new Book("American Gods","Neil Gaimen",2,"A1233454346765456");
                Book book2 = new Book("NeverWhere","Neild Gaimen",1,"A1334567654376787");
                UserInput.book.add(book3);
                UserInput.book.add(book1);
                UserInput.book.add(book2);


            }catch(Exception e){
                e.printStackTrace();
            }
        }
    }

    public void print(){
        for(Book b:UserInput.book){
            System.out.println(b.toString());

        }


    }


}

public class Book implements ILibrary{
    private String bookName;
    private String authorName;
    private int numberOfCopiesInStock;
    private String ISBN;

    //Constructor
    public Book(String bookName,String authorName,int numberOfCopiesInStock,String ISBN){
        this.bookName = bookName;
        this.authorName = authorName;
        this.setNumberOfCopiesInStock(numberOfCopiesInStock);
        this.setISBN(ISBN);
    }

    //Setters
    public void setNumberOfCopiesInStock(int numberOfCopiesInStock)throws IllegalArgumentException{
        if(numberOfCopiesInStock < MIN_NUMBER_OF_COPIES || numberOfCopiesInStock > MAX_NUMBER_OF_COPIES){
            throw new IllegalArgumentException();
        }else{
            this.numberOfCopiesInStock = numberOfCopiesInStock;
        }
    }

    public void setISBN(String ISBN)throws IllegalArgumentException{
        if(ISBN.length() < ISBN_MAX_OF_DIGITS || ISBN.length() > ISBN_MAX_OF_DIGITS){
            throw new IllegalArgumentException();
        }else{
            this.ISBN = ISBN;
        }
    }

    //Getters
    public String getBookName(){
        return this.bookName;
    }

    public String getAuthorName(){
        return this.authorName;
    }

    public int getNumberOfCopiesInStock(){
        return this.numberOfCopiesInStock;
    }

    public String getISBN(){
        return this.ISBN;
    }

    //ToString method
    public String toString(){
        return("BookName: " + getBookName()
                +"\n"
                +"AuthorName: " + getAuthorName()
                +"\n"
                +"Number of Copies: " + getNumberOfCopiesInStock()
                +"\n"
                +"ISBN: " + getISBN());
    }

}

public class Exit {

    private final String GOOD_BYE_MESSAGE = "Goodbye";

    public void exitMessage(){
        System.out.println(GOOD_BYE_MESSAGE);
    }
}

public interface ILibrary {

    int MAX_NUMBER_OF_COPIES = 2;
    int MIN_NUMBER_OF_COPIES = 0;
    int ISBN_MAX_OF_DIGITS = 17;

}

[Kevin O'Sullivan]

Norm Radder wrote:

Suppose to be added

Is that code being executed?  Add a print statement so you can see.

Also thank you for you trying to help as well.

Sorry not sure what you mean, add a print statement where? in the userinput class ?

[Norm Radder]

add a print statement where?  

Add print statements in all the places where the code is supposed to be executed to load the list that is empty in the print method.
The print outs will show you where the code is being executed or not being executed if there isn't a print out.

[Carey Brown]

This was my run with your code:

********************
*     Welcome To   *
*    Cork Library  *
********************
********************
*       Menu       *
*      Options     *
********************
1.) Add Book.            
2.) Search for Book.    
3.) Delete Book.          
4.) Display all Books.   
5.)                      
0.) Exit.                
*************************
>1
Please enter number of copies: 
1
Please enter name of book: 
name
Please enter author name: 
author
Please enter ISBN number: 
12345678901234567
book.size(): 3
Please enter number of copies: 
0
1.) Add Book.            
2.) Search for Book.    
3.) Delete Book.          
4.) Display all Books.   
5.)                      
0.) Exit.                
*************************
>4
3
BookName: name
AuthorName: author
Number of Copies: 1
ISBN: 12345678901234567
BookName: American Gods
AuthorName: Neil Gaimen
Number of Copies: 2
ISBN: A1233454346765456
BookName: NeverWhere
AuthorName: Neild Gaimen
Number of Copies: 1
ISBN: A1334567654376787
1.) Add Book.            
2.) Search for Book.    
3.) Delete Book.          
4.) Display all Books.   
5.)                      
0.) Exit.                
*************************
>0
Goodbye

[Carey Brown]

So, your code seems ok, then it is probably how it is being compiled. Make sure all .java files are saved. Remove all .class files. Do a complete re-compile. Try it again.

[Kevin O'Sullivan]

Carey Brown wrote:So, your code seems ok, then it is probably how it is being compiled. Make sure all .java files are saved. Remove all .class files. Do a complete re-compile. Try it again.

Sorry carey I should have clarified, when you first enter the program and press 4 to see what books are already available , it doesn't show the hardcoded books until after you enter one and I just realised the reason might be because those hardcoded books should be somewhere else and not in that class.

[Norm Radder]

those hardcoded books should be somewhere else

Yes, that looks like the problem.  Do you have any ideas about where that code should go so its results are available anywhere else in the program's execution?

[Kevin O'Sullivan]

Norm Radder wrote:

those hardcoded books should be somewhere else

Yes, that looks like the problem.  Do you have any ideas about where that code should go so its results are available anywhere else in the program's execution?

Would you put them in their own class prehaps ?

[Carey Brown]

I'm not sure that I like the way you've broken down your classes, but given what you have, I'd add an initLibrary() method to UserInput and call it from main().

[Norm Radder]

Cary Brown wrote:I'm not sure that I like the way you've broken down your classes

I agree.  It's like the classes were randomly created and methods add to them.

One BIG flaw in the project is the use of static.  There should only be one method that is static: main.  There should not be any static fields.

[Carey Brown]

Generally speaking a class would appear in your requirements as a noun. Therefore "library" and "book" would be suitable classes whereas "AddBook" would not. "Add", "Search", and "Delete" are verbs describing an action and are generally implemented as methods.

As Norm pointed out you (mostly) shouldn't have any static methods in your project except if you are creating a utility class that has nothing but static methods.

Here is an example of your project using my utilities "Print2" and "Kbd2". "Print2" i'm including here, "Kbd2" is a truncated version of the "Keyboard" utility you can find a link to in my signature. See how much cleaner this is and easier to follow the flow of logic?

//======================================================================
public class LibraryMain2
{
    public static void main(String[] args) {
    	new Library2().run();
    }
}

//======================================================================
class Library2
implements Constants2
{
	enum Choice { EXIT, ADD, SEARCH, DELETE, DISPLAY, NONE };
	private static final String[] MENU_CHOICES =
	{
		"1. Add Book",
		"2. Search for Book",
		"3. Delete Book",
		"4. Display all Books",
		"0. Exit"
	};

	private List<Book2>		books = new ArrayList<>();
	
	//----------------------------------------------------------------------
	public void run()
	{
		try
		{
			init();
			Print2.centeredBox(
					new String[] { "Welcome To", "Cork Library" }, 30, '=' );

			Choice choice = Choice.NONE;
			while( choice != Choice.EXIT )
			{
				Print2.leftJustifiedBox( MENU_CHOICES, 30, '*' );
				choice = Choice.values()[ Kbd2.promptIntRange( "Enter choice: ", 0, 4 ) ];
				switch( choice )
				{
				case ADD:		add();			break;
				case SEARCH:	search();		break;
				case DELETE:	delete();		break;
				case DISPLAY:	display();		break;
				case EXIT:		exit();			break;
				case NONE: // can't happen because of range check
					break;
				}
			}
		}
		catch( Exception ex )
		{
			ex.printStackTrace();
		}
		Print2.centered( "Good-Bye", 30, '=' );
	}
	
	//----------------------------------------------------------------------
	private void init()
	{
	}
	
	//----------------------------------------------------------------------
	private void add()
	{
	}
	
	//----------------------------------------------------------------------
	private void search()
	{
	}
	
	//----------------------------------------------------------------------
	private void delete()
	{
	}
	
	//----------------------------------------------------------------------
	private void display()
	{
	}
	
	//----------------------------------------------------------------------
	private void exit()
	{
	}
}

//======================================================================
class Print2
{
	//----------------------------------------------------------------------
	public static void centeredBox( String[] msg, int width, char ch )
	{
		System.out.println( repeating( ch, width ) );
		for( String m : msg )
			centeredBoxLine( m, width, ch );
		System.out.println( repeating( ch, width ) );
	}
	
	//----------------------------------------------------------------------
	public static void centeredBoxLine( String msg, int width, char ch )
	{
		int		len1 = width - msg.length() - 2;
		int		lenHalf = len1 / 2;
		int		lenOtherHalf = len1 - lenHalf;
		System.out.println( ch + repeating( ' ', lenHalf ) + msg
				+ repeating( ' ', lenOtherHalf ) + ch );
	}
	
	//----------------------------------------------------------------------
	public static void leftJustifiedBox( String[] msg, int width, char ch )
	{
		System.out.println( repeating( ch, width ) );
		for( String m : msg )
			leftJustifiedBoxLine( m, width, ch );
		System.out.println( repeating( ch, width ) );
	}
	
	//----------------------------------------------------------------------
	public static void leftJustifiedBoxLine( String msg, int width, char ch )
	{
		int		len1 = width - msg.length() - 3;
		System.out.println( ch + " " + msg
				+ repeating( ' ', len1 ) + ch );
	}
	
	//----------------------------------------------------------------------
	public static void centered( String msg, int width, char ch )
	{
		int		len1 = width - msg.length() - 2;
		int		lenHalf = len1 / 2;
		int		lenOtherHalf = len1 - lenHalf;
		System.out.println( repeating( ch, lenHalf ) + " " + msg
				+ " " + repeating( ch, lenOtherHalf ) );
	}
	
	//----------------------------------------------------------------------
	public static String repeating( char ch, int len )
	{
		StringBuilder		sb = new StringBuilder( len );
		while( --len >= 0 )
			sb.append( ch );
		return sb.toString();
	}
}

//======================================================================
interface Constants2
{
	int MIN_COPIES = 0;
	int MAX_COPIES = 2;
	int ISBN_MIN_DIGITS = 10;
	int ISBN_MAX_DIGITS = 17;
}

[Kevin O'Sullivan]

Thanks for that example carey and for the explanation, the whole reason I made the UserInput class static was because I wanted to make it a utility class, I see now I got it completely wrong and will have to go back and check my understanding of utility classes.

[Carey Brown]

Utility Classes, a general guideline:

Made up entirely of static methods.

Have no knowledge of the application's business logic.

Make no calls to the application specific code.

Only makes calls to Java libraries or other utility classes.

Ideally written in a portable manner so that it would be portable to another application.

If you find yourself bending these rules then perhaps you really aren't dealing with a clean utility situation.

[Kevin O'Sullivan]

Carey Brown wrote:Utility Classes, a general guideline:

Made up entirely of static methods.

Have no knowledge of the application's business logic.

Make no calls to the application specific code.

Only makes calls to Java libraries or other utility classes.

Ideally written in a portable manner so that it would be portable to another application.

If you find yourself bending these rules then perhaps you really aren't dealing with a clean utility situation.

Would a login class that takes a user name and password be considered a good candidate for a utility class ?

[Carey Brown]

Kevin O'Sullivan wrote:Would a login class that takes a user name and password be considered a good candidate for a utility class ?

Maybe.

Would it need to call any business logic?

Would it need to remember a state? That is, would it need its own member variables (a.k.a. fields)?

Would it need a constructor?

[Carey Brown]

Can you give me an example of what you're thinking with the methods stubbed out?