We Keep Coding

ar.readLine not reading a input from user?

Summary
1. I am import java.io.console,i am not getting any error in my code,
code is correct, I thought, It's getting some error in eclipse
software... Error :
Exception in thread "main" java.lang.NullPointerException at
loops.Escapey.main(Escapey.java:9)
Coding:
package loops;
import java.io.Console;
public class Escapey {
public static void main(String[] args) {
Console ar = System.console(); // creating a new object for console
String name = ar.readLine("how old are you ?"); //reads a user input
System.out.printf("%s - pretty age",name);
}
}
Ouput :
- I except the output how old are you ?? 18 18 - pretty age
But the actual output is getting error... Exception in thread "main"
java.lang.NullPointerException at loops.Escapey.main(Escapey.java:9)

I assume you are running this into some IDE. Since System.console returns the attached console, if you run it into IDE, it will return NULL. The better approach is to use Scanner class. If you really want to use System.console, you will have to test it on some console. If on Mac, run the terminal. On Linux any of the terminal apps would work.

If we run this in IDE (Intellij), it is throwing null pointer exception. Since this is related to console, I tried to execute this in command line and it works fine.
Execute these steps in terminal or command line and it will work
1) javac Escapey.java
2) java Escapey

Cannot connect to database Error: java.sql.SQLException: [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified

I am having errors with connecting to a MS Access Database (CDCollection.accdb) from Java. The IDE we are using is Netbeans. I have done research on possible solutions as to the error, but due to being inexperienced in the topic, I am not too sure how to solve it. The rest of my class are having the same problem and the teacher does no know how to solve the problem either.
My class is now in the final chapter, Learning Unit 10: Accessing a Database from a Java program, of Funworks's exploring IT: Java Programming. Grade 11.
I would post links to the three sources I have found most useful, but Stack Overflow says I need to have 10 reputation points to post more than 2 links. I have searched both Stack Overflow and the web to find the solution to this error, but those were more advanced than where I currently am.
Edit: Here are the links, thanks to those who upvoted me. The solution they suggest makes sense, but does not seem to work...
http://community.microfocus.com/borland/managetrack/starteam/w/knowledge_base/16933.error-java-sql-sqlexception-microsoft-odbc-driver-manager-data-source-name-not-found-and-no-default-driver-specified.aspx
http://www.coderanch.com/t/440574/JDBC/databases/java-sql-SQLException-ODBC-Driver
http://www.codeproject.com/Articles/35018/Access-MS-Access-Databases-from-Java
From what I understand, it is due to the school computers and my laptop all being 64-bit and ODBC (Open DataBase Connectivity) being 32-bit. My teacher does not know how to solve this problem, as it is her first time encountering it. When the grade 11s of last year reached this section of the book, the school computers were still 32-bit.
According to what I've read, I need to go to the OBDC Data Source Administrator and, under the System DSN tab, add "Microsoft Access Driver (*.mdb, *.accdb)". I noted that it was already there under the User DSN tab.
Find the OBDC Data Source Administrator at C:\Windows\SysWOW64\odbcad32.exe or Control Panel\System and Security\Administrative Tools\Data Sources (ODBC). The first is preferable, as it seems to have more Drivers available even though the Control Panel shortcut targets the same executable file.
However, I still get the same error once I have added the driver.
Here is my code:
The DB class
package cd;
import java.sql.*;
public class DB
{
private static final String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
private static final String url = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ={CDCollection.accdb}";
private Connection connection;
private PreparedStatement statement;
private ResultSet resultSet;
public DB()
{
try
{
Class.forName(driver);
System.out.println("Driver successfully loaded");
}
catch (ClassNotFoundException c)
{
System.out.println("Unable to load driver");
System.out.println(c);
}
try
{
connection = DriverManager.getConnection(url);
System.out.println("Connection successful");
}
catch (SQLException e)
{
System.out.println("Unable to connect");
System.out.println(e);
}
}
}
And the UseDB class:
package cd;
import java.sql.*;
public class UseDB
{
static DB db = new DB();
public static void main(String[] args)
{
}
}
For the
DBQ={CDCollection.accdb}
I have tried the full path to the file (C:\Users\\Documents\IT\Java\Databases\CD\CDCollection.accdb), using the double backslash due to the first marking an escape character. I have also tried with forward slashes (/) and I have tried without a path, as it is in the code, and placing the database in the \CD (the project folder), \CD\src (the source folder), \CD\src\cd (the package folder).
Yet, despite this, I and my classmates still get the same output every single we run the program:
run:
Driver successfully loaded
Unable to connect
java.sql.SQLException: [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified
BUILD SUCCESSFUL (total time: 0 seconds)
Could I please have help? Keep in mind that my class has only just started this module today; we have only been doing Access and SQL for 1 month and have been doing Java for a year and a half.
Thank you!

I would suggest you adding a SYSTEM DATASOURCE at ODBC configuration panel. Let's suppose you name it cdcollection. Then your url variable just needs to be:
private static final String url = "jdbc:odbc:cdcollection";
Here's a a nice STEP BY STEP article on how to do just that.
Welcome to StackOverflow.

Issues with running a compiled java program

I am a Java beginner. I wrote a quintessential "Hello, World!" program. It compiles, but won't run. The terminal says there is an exception in the thread main, and that the class hello is not found. I am using Ubuntu 12.04. What could be wrong here?
The file is called hello.java.
The commands I used:
$javac hello.java
$java hello
My code is below:
class hello{
public static void main(String[] args) {
system.out.print("Hello");
}
}
EDIT-----------------------------------------------------------------------------------------
I just realized that I am using openjdk7. Does that pose a problem?

class must be: public class hello
system.out.print is wrong, must be: System.out.println("Hello World");

Is the filename hello or Hello? The only way I duplicated your problem was by having the class name wrong, and in java the class name an filename must exactly match (meaning the case too). So if your filename is Hello.java and the class name is hello the program will compile fine but throw the same error you mentioned. This is just a guess though.

Is that all your code? Since you use a terminal, can you add the results of the command ls -lR to your question? (run it in the same directory as your original command executing the application).

Getting "class does not have a static void main method accepting String[]" error even though main signature is correct

My DrJava was working fine, but now I keep getting the folowing error whenever I run anything:
Static Error: This class does not have a static void main method accepting String[].
So it will compile OK, but then it shoots out the error . This happens even though everything I test does indeed have a public static void main(String[] args) in it. It seems like a classpath/resources type of error. I appreciate any tips
EDIT: my class
public class Test{
public static void main(String[] args){
System.out.println(" hashmap ");
}
}

There's nothing wrong with the code, so the problem must be with the environment.
Check that you're actually executing that class. Find out where the class that's executed is specified and check it's correct
Check that you're compiling the class. Maybe the code you're looking at has not been compiled and you're trying to execute an old version that was compild before you coded a main()
Check your classpath. Is the compiled class accessible in the classpath of the java command

You don't need to reinstall java, nor is it a java version issue. It may be the way that your are running the program.
To check if it is a problem with your code, do the following:
Make a new folder and put Test.java in it.
Open up Command Line Or Terminal and change to that folder .
Type javac Test.java. Test.class should be in the folder now.
If you want, open up the class with a text editor. This is what I get:
˛∫æ2
<init>()VCodeLineNumberTablemain([Ljava/lang/String;)V
SourceFile Test.java hashmap Testjava/lang/Objectjava/lang/SystemoutLjava/io/PrintStream;java/io/PrintStreamprintln(Ljava/l ang/String;)V! *∑±
% ≤∂±
Back to the command line or terminal, type java Test.
If you get an error, which you shouldn't, I don't know what to say. It should produce the string " hashmap " on to the command line or terminal.
Why re-installing Dr. Java may not work is because you may be using the same working directory, causing same run settings to be used. Dr. Java may be running an external program, one without a main method.
I think that you should install the Eclipse IDE for Java. It is much easier to get around, it looks nicer, and it runs the file or project that you are looking at currently.

Sometimes this problem happens because may be mistake in saving file.you always your file using double quotes and with the .java extension which is main class means that class containing main method.
you should save your file by class name which is public .if there is two classes and both have main method then you should save your file by class name that is public and that class will be run.As like your compiler looking for main method in public static void main(String [] args) that is contract for jvm to run a programme
so it is not able to found that main method that is static and it looking for your Dr class.java
See this Example it have two main methods and practice these kinds of question.I also got this kind of problem in starting.
public class TestFirst
{
public static void main(String [] args){
System.out.println(" TestFirst ");
}
}
class Test{
public static void main(String [] args){
System.out.println(" hashmap ");
}
}
if you save pro-gramme by "TestFirst.java" then o/p will come TestFirst if you do some mistake in main method because we have saved our programme by TestFirst then you will get error like you got.
# 2nd mistake may be this
debian#debian:~/Geany_java$ javac Test1.java
debian#debian:~/Geany_java$ java Test1
Exception in thread "main" java.util.NoSuchElementException
at java.util.StringTokenizer.nextToken(StringTokenizer.java:349)
at Test1.main(Test1.java:11)
your classpath has not set properly See above Compiling successfully but running showing same kind of error you got.Which OS is using I can guide you properly.

Check that actually your file have the .java termination nor the .dj

There is nothing wrong with the code.
It is the executing environment which might have problem. Please share the details.

Check if program compiled correctly.
Check time-stamo of .class file.
Check permissions on folder/directory where class-files are getting generated.
Check if DrJAVA has appropriate permission on the directory.
Did you create a file, compiled it with out main?
Check class-path. Might be possible that previous class file is still being found by JDK in classpath.
Try compiling .java file from cmdLine instead of editor.

As others have mentioned, your code is fine. There must be a problem with your environment. I recently experienced a similar issue when investigating and answering this question.
Basically, in that question, the code Void.class instanceof Class resulted in a compiler error because a user-made Class.class existed in the classpath, so one Class (the Java built-in java.lang.Class) didn't match with the given Class (user-made).
Something similar may be at work here. It is possible that there is a user-made String.class in your classpath. Then in your main signature, String[] args would mean an array of your String, when Dr. Java must be looking for a main method taking an array of the Java built-in String, i.e. java.lang.String[]. If you have a custom String class in your classpath (or in your project?), then the Java compiler will choose it over the built-in String. If you were to compile and run your Test class from the command line, then you would get the runtime error: Exception in thread "main" java.lang.NoSuchMethodError: main.
Following #S0urceC0ded's suggestion, you may find this when looking at Test.class in a text editor:
main([LString;)V // A user-made String class
instead of what it's supposed to be:
main([Ljava/lang/String;)V // The built-in java.lang.String class
If so, remove your own String class (at least the .class file, but also the .java file so the .class file isn't re-created) from the classpath, and compile and run your Test class again.
Without a look at your environment, I can't tell for sure that this is the issue. But it can explain it.

If you are using Dr.Java as IDE, then you need to make sure that the main class containing 'public static void main' should be at the very top of your program. Otherwise Dr.Java throws this error during runtime.

lwjgl 101: How can I write the basics?

EDIT: So apparently I was doing everything right, but I had a different problem that made it look as if I was doing something wrong. Sorry about that. --me, newbie
This ought to be really simple, but I cannot for the life of me figure out how to compile anything with lwjgl and have it work. I can write something like
package gwison;
import org.lwjgl.Sys;
public class G
{
public static void main(String[] args)
{
System.out.println(Sys.getTime());
}
}
and I can easily compile a program with several classes in different packages, as long as I wrote all the classes myself. But I have no clue how to make G work. I think it has something to do with classpathes? Maybe? Help?
I really have been searching for hours, but the most basic tutorials assume you know how to do this!
Edit: oh and I'm sorry if I've violated stackoverflow conventions; I did try not to but this is my first action here.

You can try out this way create a folder called TestProject inside it create one folder
gwison like D:\TestProject\gwison
Create two more folder in same TestFolder like this D:\TestProject\org\lwjgl.
Now create a Class G in gwison folder like u created above.Create one more class Sys like this
package org.lwjgl;
import java.util.Date;
public class Sys {
public static Date getTime(){
return new Date();
}
}
now from command promt go to this path D:\TestFolder and run the below command:
javac gwison\G.java
This will complie your code, now run one more command:
java gwison.G
This will run your code without any error and you will get a output like this:
Sun May 02 13:17:11 IST 2010

You need to make sure the jars are in the classpath while compiling and running.
Place your lwjgl jars in the classpath during compilation
More info :
http://en.wikipedia.org/wiki/Classpath_%28Java%29