Have you installed JDK? If so, set the "JAVA_HOME" to your JDK installation folder. Set the "path" to the bin folder of the JDK folder. Set the "CLASSPATH" to whatever location you have classes or JAR files which you need to invoke when compiling/running a java application.
Eclipse doesn't need the PATH, CLASSPATH and JAVA_HOME environment variables.
If you want to run the Java compiler and other tools from the JDK from the command line, then you should add the 'bin' directory of the JDK to your PATH. See the JDK installation instructions for details.
The CLASSPATH is used by Java to find class files to load. You normally should not set it at all.
The JAVA_HOME variable is not needed for most Java software. Some software wants this to be able to find the JRE. If you have installed the JDK, you could make it point to the JDK installation directory. But I wouldn't set it unless I would have software that specifically asks for it.
Originally posted by Jesper Young: Eclipse doesn't need the PATH, CLASSPATH and JAVA_HOME environment variables.
True. But you can if required. In the run dialog you can do it through the classpath and environment tabs. Since the OP mentioned "Today I installed Eclipse.." I was trying to confirm where exactly these settings need to go.