how do i run java programs using the terminal to add more ram to the program?

Hi please try to use this command:
java -jar /path/to/file.jar

Change /path/to/file.jar witht the path of your file before.

You can also try to do this:
http://manoharbhattarai.wordpress.com/2010/09/23/execute-java-program-in-ubuntu-from-terminal/

iv tried both and they didnt work do you have a more simple way to explain it, im kinda new to usimg the terminal

What's the name of your java file ?

The name of the java file is easy: Minecraft.jar .

From http://www.minecraft.net/download.jsp.
(1) It says that the Sun JVM is required. That would be a package with a name like sun-java6-jre. The default jre (Java Runtime Environment) is probably openjdk instead (depending on your Ubuntu version).
(2) Once you have a jre in place, find the path to the java executable. If your system has two JREs you will need the path to run the correct version. If you have only one JRE, then life is easier and you can ignore this step.
(3) Download Mincraft.jar
(4) Use the command line
% ${PATH_TO_JAVA}/java -Xmx1024M -Xms512M -cp Minecraft.jar net.minecraft.LauncherFrame

whats the default path to java?

You can simply use "java".
Else open a terminal and type "which java".

i tried everything the jre location is /urs/bin/java what command do i need to use?

im kinda new at using the terminal

Try
% echo $PATH
should respond with a :-separated list of directories and one of these should be /usr/bin. Paste the result as an added comment here in Launchpad.

Try
% java -version
% /usr/bin/java -version
Paste the results as an added comment here in Launchpad.

If your Minecraft.jar is in the current working directory
% /usr/bin/java -Xmx1024M -Xms512M -cp Minecraft.jar net.minecraft.LauncherFrame

If Minecraft.jar is in a different directory, say /home/yourname/foo/mine.
% /usr/bin/java -Xmx1024M -Xms512M -cp /home/yourname/foo/mine/Minecraft.jar net.minecraft.LauncherFrame

For many programs, the -X arguments are not needed. Minecraft is a memory pig. There are two kinds of memory, heap and stack. When running a program, it's best to follow user instructions when setting these. The -cp <path> argument pair is a path to the Java classes you wish to run. In this case, the classes are inside a jar file -- a kind of software bottle. net.minecraft.LauncherFrame is an argument to the Minecraft program.

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

java version "1.6.0_22"
OpenJDK Runtime Environment (IcedTea6 1.10.2) (6b22-1.10.2-0ubuntu1~11.04.1)
OpenJDK Client VM (build 20.0-b11, mixed mode, sharing)

% java -Xmx1024M -Xms512M -cp /home/yourname/foo/mine/Minecraft.jar
should work. The -Xmx1024M is adding more ram to your program. That's 1024 Megabytes of heap space. If you need more, change it to -Xmx1500M. I don't know what the upper limit is.