java looping problem?

whenever i try to do a loop in java, it does this wierd thing where it repeats the printed lines multiple times. this is a problem for me because everytime my instructor asks us to make a program that uses a loop(most every program we make now) he sees this and says it's a probem. i asked him how to fix it but he either doesnt know or expects us to figure it out on our own(everybody else is having the same problem). here's an example:

Code:

---

import java.io.*;
class password {
        public static void main (String args[])
        throws java.io.IOException {
               
                char input, passwd='y';
               
                do {
                System.out.print("Enter your password: ");
                input=(char)System.in.read();
            if(input!=passwd) System.out.print("wrong password");
                }
                while(input!=passwd);
               
        System.out.println("you got it");
        }
        }

---

will output this if you enter the wrong password

Quote:

---

wrong passwordEnter your password: wrong passwordEnter your password: wrong passwordEnter your password:

---

and then the user can input another letter

what it should do is just say "wrong password" and then wait for input again... anybody know what the problem is?

Try this code instead. System.in.read() is a strange beast that should not be used. If you need to accept console input, use a BufferedReader instead.

Code:

---

import java.io.*;
class password
{
        public static void main (String args[])        throws java.io.IOException
        {
               
                char input, passwd='y';

                do
                {
                        System.out.print("Enter your password: ");
                        input=(char)new BufferedReader(new InputStreamReader(System.in)).read();
                            if(input!=passwd) System.out.println("wrong password");       
                       
                }
                while(input!=passwd);
               
        System.out.println("you got it");
        }
}

---

EDIT: In case you didn't understand the code, it can be broken up into this:

Code:

---

import java.io.*;
class password
{
        public static void main (String args[])        throws java.io.IOException
        {
               
                char input, passwd='y';
                InputStreamReader isr = new InputStreamReader(System.in);
                BufferedReader buf = new BufferedReader(isr);
                do
                {
                        System.out.print("Enter your password: ");
                        input=(char)buf.read();
                            if(input!=passwd) System.out.println("wrong password");       
                       
                }
                while(input!=passwd);
               
        System.out.println("you got it");
        }
}

---

Cheers,
cgkanchi

ill try it out, thnx

i just compiled and ran urs and it does the same thing:

Quote:

---

bash-2.05b# java password
Enter your password: a
wrong password
Enter your password: wrong password
Enter your password:

---

it seems like the more characters i input the more screwy responses i get before it asks for input again.
"aaaa" gets me:

Quote:

---

bash-2.05b# java password
Enter your password: aaaa
wrong password
Enter your password: wrong password
Enter your password: wrong password
Enter your password: wrong password
Enter your password: wrong password
Enter your password:

---

I compiled his and it works fine:

Code:

---

Enter your password: aaaa
wrong password
Enter your password: aaaa
wrong password
Enter your password: aaaa
wrong password
Enter your password: d
wrong password
Enter your password: d
wrong password
Enter your password: ssads
awrong password
Enter your password: das
wrong password
Enter your password: y
you got it

---

oops, i must have swiped the wrong code when i copy and pasted that :D sry bout that

edit
wierd, the first code you wrote worked, but the second one still messes up. they're supposed to be the same right?

hey, what if i wanted to have a password thats more than just one char? how would i go about that?

Haven't tested this, just edited it quickly... should work:

Code:

---

import java.io.*;
class password
{
        public static void main (String args[])        throws java.io.IOException
        {
               
                String input, passwd="whateveryouwant";
                InputStreamReader isr = new InputStreamReader(System.in);
                BufferedReader buf = new BufferedReader(isr);
                do
                {
                        System.out.print("Enter your password: ");
                        input=(String)buf.read();
                            if(!input.equals(passwd)) System.out.println("wrong password");       
                       
                }
                while(!input.equals(passwd));
               
        System.out.println("you got it");
        }
}

---

;TT :
It should be buf.readLine() for String input. BufferedReader.read() only works for int's and char's.

Phonedog911:
Strange. I tried it out and get the same thing. Both are supposed to be equivalent. Looks interesting... I'll play a bit and get back to you.

Cheers,
cgkanchi

I'm gonna have a try at it, see how this works

Code:

---

import java.util.Scanner;

public class Password
{
        public static void main (String args[])
        {
               
                Scanner kbd = new Scanner(System.in);
               
                String passwd= new String("whateveryouwant");
                String input;
               
                do
                {
                        System.out.print("Enter your password: ");
                        input=kbd.nextLine();
                            if(!input.equals(passwd)) System.out.println("wrong password");       
                       
                }
                while(!input.equals(passwd));
               
        System.out.println("you got it");
        }
}

---

[/B][/QUOTE]

Compiled and works perfectly, but you need Java 1.5.0 [there's a stable release now] to use this.

hypronix, I've never seen the Scanner class before. Is it a new class added in Java 2 v5? I haven't yet explored it :D.

Cheers,
cgkanchi

Quote:

---

Originally posted here by cgkanchi
hypronix, I've never seen the Scanner class before. Is it a new class added in Java 2 v5? I haven't yet explored it :D.

Cheers,
cgkanchi

---

Yup! Wouldn't work on anything else, but if you tried that code [I did :)] you'd see it runs smoothly... I haven't been exposed to any other form since I've just started out studying Java about a month ago [had the first midterm two days ago :)]. But yeah, it was first released in 1.5 beta 1, used to get called as:

Code:

---

Scanner varName = Scanner.create(System.in);

---

but in the stable version it gets called like so

Code:

---

Scanner varName = new Scanner (System.in);

---

I s'ppose you could pass some other argument to it [not just System.in] but that's the only one I used so far.

Quote:

---

Originally posted here by cgkanchi
;TT :
It should be buf.readLine() for String input. BufferedReader.read() only works for int's and char's.

Phonedog911:
Strange. I tried it out and get the same thing. Both are supposed to be equivalent. Looks interesting... I'll play a bit and get back to you.

Cheers,
cgkanchi

---

Knew I'd make a mistake like that... I was taught input using the cs1.jar package so good eye.

thanx for the input, the teach has taught us to only use a buffered reader when you need to parse the input into an integer, we've been using system.in.read() for characters and he really should have said something if he wanted us to do it this way...

Quote:

---

Originally posted here by hypronix
But yeah, it was first released in 1.5 beta 1, used to get called as:

Code:

---

Scanner varName = Scanner.create(System.in);

---

but in the stable version it gets called like so

Code:

---

Scanner varName = new Scanner (System.in);

---

---

You were correct in you assumption. Now you can scan from Files, String and Readables in addition to streams.
As far as the visible change, from method call to constructor, they were using a factory to create them before, meaning that the one method (create()) did all of the hard work for you, my guess is that they changed it from an extendable or abstract class/interface into a final class and decided to make the constructors public because they can't be extended now, and besides a factory isn't necessary in a final class, because the purpose of a factory is to return an instance of the proper sub-class.

If you would like to know more about factory patterns or any of the many other software design patterns and their many benefits check out some of these sites:
http://www.dofactory.com/patterns/Patterns.aspx
http://hillside.net/patterns/
http://www.cs.wustl.edu/~schmidt/patterns.html
and many, many more...