There are several ways to run DrJava:
DrJava requires a Java 2 v1.4 or later virtual machine. (Note: The JDK, not the JRE, must be installed to have access to compilation in DrJava.) If you need to download a JVM, we recommend Sun's JDK 5.0 for Solaris, Linux and Windows. Other users should use the Java virtual machine that comes with their operating system (including MacOS X).
Also, DrJava uses two Java Virtual Machines (one for the main program, and one for the Interactions Pane) that use Java's Remote Method Invocation (RMI) to communicate with each other. RMI uses TCP/IP as the default transport mechanism, so you must have those drivers installed. Without TCP/IP, DrJava will not start properly.
See the FAQ page for more details on system compatibility.DrJava has been partially funded by the National Science Foundation, the Texas Advanced Technology Program, and Sun Microsystems, Inc.