Doesn't returning the localhost IP address

[rootnet47]

Hi! I'm new to Java as well as Linux. well, I've written a program to return the localhost IP address as describes bellow

import java.net.*;

class pg1
{
	public static void main (String[] args) throws UnknownHostException
	{
		InetAddress ia = InetAddress.getLocalHost ();
		System.out.println (ia);
	}
}

After that I compiled the code successfully but once I tried to run the program it bugs as

ricky@ricky-Rev-1-0:~/Desktop/java$ javac pg1.java
ricky@ricky-Rev-1-0:~/Desktop/java$ java pg1
Exception in thread "main" java.lang.UnsupportedClassVersionError: pg1 : 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: pg1. Program will exit.

I ran the same code in Windows OS successfully.

Could anyone help me to solve the problem?

[Hibernate]

Hi! I'm new to Java as well as Linux. well, I've written a program to return the localhost IP address as describes bellow

import java.net.*;

class pg1
{
public static void main (String[] args) throws UnknownHostException
{
InetAddress ia = InetAddress.getLocalHost ();
System.out.println (ia);
}
}

After that I compiled the code successfully but once I tried to run the program it bugs as

ricky@ricky-Rev-1-0:~/Desktop/java$ javac pg1.java
[⋅⋅⋅]
at java.lang.ClassLoader.loadClass(ClassLoader.java:2 66)
Could not find the main class: pg1. Program will exit.

I ran the same code in Windows OS successfully.

Could anyone help me to solve the problem?

Oi, it works: Zenith/127.0.1.1
(Yes, my computer is called Zenith because it is above yours. (my virtual ones are called Nadir))

But you should have public on the class: public class pg1

[Hibernate]

Are you using Java 7 or Java 6.
Maybe Java 7 is more strict in have the class public, I can't get Java 7 to work, Java 6 does not seem to require it.

[Hibernate]

Off topic: As you are new to Linux I would suggest not to use GNOME 3 or Unity, I think they will either kill you, make you kill yourself or make you kill GNU/Linux. Use GNOME 2 or KDE.

[rootnet47]

I tried with "public class pg1"
It doesn't work so.

[rootnet47]

I'm using Java 7

[Hibernate]

Humm...

Is your Java installation a clean installation or an update?
How did you install Java?

What is the output of (run in terminal)?:

update-alternatives --display java

[rootnet47]

Well I'm still using GNOME 3.1.4 but what's wrong with GNOME 3?

[rootnet47]

Is it right?


ricky@ricky-Rev-1-0:~/Desktop/java$ update-alternatives --display java
java - auto mode
link currently points to /usr/lib/jvm/java-6-openjdk/jre/bin/java
/usr/lib/jvm/java-6-openjdk/jre/bin/java - priority 1061
slave java.1.gz: /usr/lib/jvm/java-6-openjdk/jre/man/man1/java.1.gz
/usr/lib/jvm/java-7-openjdk/jre/bin/java - priority 1051
slave java.1.gz: /usr/lib/jvm/java-7-openjdk/jre/man/man1/java.1.gz
Current 'best' version is '/usr/lib/jvm/java-6-openjdk/jre/bin/java'

[Hibernate]

Well I'm still using GNOME 3.1.4 but what's wrong with GNOME 3?

Just very uncomfortably and working it gets every inefficient.
Also features I think very high of have been disabled/removed.

[Hibernate]

Is it right?


ricky@ricky-Rev-1-0:~/Desktop/java$ update-alternatives --display java
java - auto mode
link currently points to /usr/lib/jvm/java-6-openjdk/jre/bin/java
/usr/lib/jvm/java-6-openjdk/jre/bin/java - priority 1061
slave java.1.gz: /usr/lib/jvm/java-6-openjdk/jre/man/man1/java.1.gz
/usr/lib/jvm/java-7-openjdk/jre/bin/java - priority 1051
slave java.1.gz: /usr/lib/jvm/java-7-openjdk/jre/man/man1/java.1.gz
Current 'best' version is '/usr/lib/jvm/java-6-openjdk/jre/bin/java'

So you are really using Java 6 and not Java 7.

You can use the command

update-alternatives --config #

to configure to use either Java 6 or Java 7.
Replace # with java, javac, jar and then javadoc.
(and other Java tools I do not think you will be using for a while like javah and javap).

[rootnet47]

Originally Posted by Hibernate's Avatar
Hibernate
So you are really using Java 6 and not Java 7.

You can use the command
Code:

update-alternatives --config #

to configure to use either Java 6 or Java 7.
Replace # with java, javac, jar and then javadoc.
(and other Java tools I do not think you will be using for a while like javah and javap).

oot@ricky-Rev-1-0:/home/ricky# update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).

Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 auto mode
1 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 manual mode
2 /usr/lib/jvm/java-7-openjdk/jre/bin/java 1051 manual mode

Press enter to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/lib/jvm/java-7-openjdk/jre/bin/java to provide /usr/bin/java (java) in manual mode.

did I select the correct one?

[rootnet47]

and WOW! My program is working, it returns the IP.

ricky@ricky-Rev-1-0:~/Desktop/java$ javac pg1.java
ricky@ricky-Rev-1-0:~/Desktop/java$ java pg1
ricky-Rev-1-0/127.0.1.1

Its good.

But I don't understand what is just append? Why its running now?

[Hibernate]

I would guess that you have complied with Java 7 and executed with Java 6 meaning that you ran on a version of Java older (in major version) then the program was compiled with
making it incompatible.

[rootnet47]

Thank you! Thanks helping.

[rootnet47]

Oh yeah, as u mentioned about GNOME 3, I got another problem with GNOME 3 that whenever I try to install Fedora 15 GNOME 3 (x86 or x86_64) in my pc (lenovo Y560, I've tried in Dell XPS also) it messaged as "GNOME 3 failed to load. Your HD is not able load GMOME 3". Did you ever face such problem (but in case of ubuntu 11.10 alpha 3 with GNOME 3 load properly).

[Hibernate]

No I never faced any problems, but I'm using Arch Linux. (If you decide to test Arch Linux, be aware that is it a nuclear playground for geeks and you should test it on a virtual computer first and save an installation manual which you can access during installation on a physical computers.)

It sounds weird that your hard drive should fail to load GNOME 3.

[rootnet47]

Not hard drive it was hardware, I think, the message points to graphics card or HD accelerator.

[Tolls]

Summary:
A ClassVersion error is entirely down to you compiling in one version and then attempting to run the code in an earlier version of Java.
In your case it was compiled under 7 and you tried to run under 6.
48 is 1.4, 49 is 1.5, 50 is Java 6, and 51 is Java 7.

[Hibernate]

That is some weird numbering (not really, but it should be improved.).