A JDK must be present on Red Hat Enterprise Linux systems. See http://kbase.redhat.com/faq/FAQ_54_4667.shtm for more information. While almost any JDK is sufficient, installing one of these JDKs is recommended:
For 32-bit Red Hat Enterprise Linux 4 platforms, a pre-packaged binary distribution of the 32-bit version of the IBM JDK 1.5.0, the java-1.5.0-ibm-devel rpm package, is available through either the Red Hat Enterprise Linux AS (v. 4 for x86) Extras Red Hat Network channel or the Red Hat Enterprise Linux ES (v. 4 for x86) Extras Red Hat Network channel.
A similar package is available for 64-bit Red Hat Enterprise Linux 4 platforms. This package is available through either the Red Hat Enterprise Linux AS (v. 4 for AMD64/EM64T) Extras Red Hat Network channel or the Red Hat Enterprise Linux ES (v. 4 for AMD64/EM64T) Extras Red Hat Network channel.
After installing the JDK, run /usr/sbin/alternatives --config javac as root to ensure that a JDK is available.