Problem running Simple Hello world program in Ubuntu

[teete]

Problem running Simple Hello world program in Ubuntu...

I have installed JDK7... copied it to /usr/lib/jvm/ directory and changed the Java Alternative

And use javac command to compile the program and it created a hello.class file

javac hello.java

it compiled without any error

below is the code

class hello{ 
 public static void main(String[] args) 
 { 
 System.out.println("Hello World!"); 
 } 
}

But when i try to run the prgram using this command

java hello

But i get this following errors

Exception in thread "main" java.lang.UnsupportedClassVersionError: Hello : Unsupported major.minor version 51.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
	at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: Hello.  Program will exit.

At last line it says Could not find the main class: Hello. Program will exit.

Please help me ,i'm new to Java

[eRaaaa]

UnsupportedClassVersionError: Hello : Unsupported major.minor version 51.0

It look likes your Java Runtime version(6) is different to your JDK version(7).
What says "java -version" in your terminal? (6?)
You have to change it....

[teete]

It look likes your Java Runtime version(6) is different to your JDK version(7).
What says "java -version" in your terminal? (6?)
You have to change it....

After executing that command ,i got following text

java version "1.6.0_24"
Java(TM) SE Runtime Environment (build 1.6.0_24-b07)
Java HotSpot(TM) Client VM (build 19.1-b02, mixed mode, sharing)


Im using JDK 7

[eRaaaa]

Yes, that was what I suspected ->
How do you changed the java alternative?
sudo update-alternatives --config java ?
Do you have selected the java 7 jre?
How To Install Oracle Java 7 (JDK) In Ubuntu ~ Web Upd8: Ubuntu / Linux blog
+ many other sites will give you an installation guide!

[teete]

Yes, that was what I suspected ->
How do you change the java alternative?
sudo update-alternatives --config java ?
Do you have selected the java 7 jre?
How To Install Oracle Java 7 (JDK) In Ubuntu ~ Web Upd8: Ubuntu / Linux blog
+ many other sites will give you a installation guide!

Thanks a lot .....thank you very much....
i had to change the java alternative,it was set to /usr/lib/jvm/java-6-sun/jre/bin/java
changed it to /usr/lib/jvm/jdk1.7.0/bin/java

so now it works ...thank you :)