compiling a java program

[chaitanya525]

hello friends,
i am new to ubuntu. I want to compile my java program in ubuntu.so i installed open jdk 1.7 in ubuntu through sudo apt-get install command.
My java program is
class Hai
{
public static void main(String s[])
{
System.out.println("hai");
}
}
But when i am compiling with javac there is no problem.
But with java command i am getting this error:
Exception in thread "main" java.lang.UnsupportedClassVersionError: Hai : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java :634)
at java.security.SecureClassLoader.defineClass(Secure ClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader .java:277)
at java.net.URLClassLoader.access$000(URLClassLoader. java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java: 212)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.j ava:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:3 21)
at sun.misc.Launcher$AppClassLoader.loadClass(Launche r.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:2 66)
Could not find the main class: Hai. Program will exit.
This code was run successfully in windows. But in ubuntu with openjdk i am getting this error. Please help me......................

[The Cog]

That looks as though you might have two different java installations there. Can you post the output of these two commands?

java -version
javac -version