You will need to install a Java development environment on your home computer. The expected tool is Dr. Java but you may also BlueJ if needed.
1. You need to get the Java Development Kit (JDK) first. This installs the Java language, compiler, libraries, etc. Go to Oracle.com and select the version that is appropriate for your computer. It is a goo idea to restart your computer after this installation to make sure it is properly installed.
2. Copy this file, Dr. Java jar file, to your desktop or go to http://drjava.org/ and download the appropriate file.
3. Run Dr. java and try a Hello World program to make sure all is working. If you are on a Mac, you may need to go into your security settings and give the program permission to run.