[SOLVED] [newbie] NullPointerException

[jon80]

I got this example out of a book, any idea why it is causing a null pointer exception?

Is it possible to dispose of the passwd variable rather than filling it with blanks?

:confused:

import java.io.*;
public class ConsoleLogon {

	
	public static void main(String[] args) {
		
		Console cons = System.console();
		String userName = cons.readLine("User name: ");
//Error: 
//Exception in thread "main" java.lang.NullPointerException
//	at ConsoleLogon.main(ConsoleLogon.java:8)

		char[] passwd = cons.readPassword("Password: ");
		
		if (userName.equals("joe") && passwd.equals("joe"))
			System.out.println("Logon successful");
		else
			System.out.println("Logon failed");
		
		//fill password field with blanks so as to remove it from memory
		java.util.Arrays.fill(passwd, ' ');

	}

}

Reference:
Core Java Volume I Fundamentals 8th Ed. (77)

[OrangeDog]

Are you actually running it with a console?

[Eranga]

And is this the complete error message you get?

[jon80]

I was not compiliing it within the command line (console), thanks Orange.

Is the line
if (userName.equals("joe") && passwd.equals("joe") correct, because somehow the logic is evaluating to the "logon failed" part?

[mtyoung]

end of if statement missig ")"

[Eranga]

(userName.equals("joe") && passwd.equals("joe")[B])[/B]

[jon80]

It's there. Tried to use builder as well, but I get confusing results:

import java.io.*;
public class ConsoleLogon {

	//NOTE: Run this from the command line not in eclipse.
	
	public static void main(String[] args) {
		
		
		Console cons = System.console();
		String userName = cons.readLine("User name: "); //NOTE: bug!
		StringBuilder builder = new StringBuilder();
		
		char[] passwd = cons.readPassword("Password: ");		
		builder.append(passwd);
		//debug
		System.out.println("DEBUG: passwd=" + passwd.toString());
		System.out.println("DEBUG: builder=" + builder.toString());

		//if (builder=="joe") System.out.println("DEBUG: bingo");  Crashes the program

		if (userName.equals("joe") && builder.equals("joe"))
			System.out.println("Logon successful");
		else
			System.out.println("Logon failed");
		
		//fill password field with blanks so as to remove it from memory
		java.util.Arrays.fill(passwd, ' ');
		
		

	}

}

Output:
Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\Administrator\Desktop\Java_playground>dir
Volume in drive C has no label.
Volume Serial Number is 982D-F9F4

C:\Users\Administrator\Desktop\Java_playground>jav ac ConsoleLogon.java

C:\Users\Administrator\Desktop\Java_playground>jav a ConsoleLogon
User name: joe
Password:
DEBUG: passwd=[C@190d11
DEBUG: builder=joe
Logon failed

C:\Users\Administrator\Desktop\Java_playground>

[Supamagier]

DEBUG: passwd=[C@190d11

System.out.println("DEBUG: passwd=" + passwd.toString());

passwd is a char array - you're printing the reference to that array.
To convert the char array into a String, use

new String(passwd);

[RamyaSivakanth]

Hi ,
Along with what he has suggested above ,Change the condition checking also to make it work.
Use the below if condition and try
if (userName.trim().equalsIgnoreCase("joe") &&
builder.toString().trim().equalsIgnoreCase("joe"))

-Regards
Ramya