Welcome Jorge.
This is a Java-Developer speaking.

edit /etc/profile
Code:
JAVA_HOME=/usr/local/java
PATH=$PATH:/usr/local/java/bin
export JAVA_HOME
export PATH
I used 'java' instead of 'j2sdk1.4.0-4-beta-alpha.linux-bla' because of 2 reasons:
1) To lazy to tip it in.
2) I recommend to create a symbolic link:
Code:
ln -s /usr/local/j2sdk1.4.0-4 /usr/local/java
Then you may install a jdk1.5 parallel, and just change the link, to test the tiger.
But the path and JAVA_HOME (which is important) still point to the right direction.

If you don't like this solution, just specify the complete path in 'profile'.

You needn't restart the system.
To read the profile again, you can source /etc/profile.
But perhaps on user (or root) -level the system-variables have been manipulated after reading profile (~/.profile, /etc/bashrc, ~/.bashrc, ~/.bashlogin)
I guess a re-login will work.

P.S.: I made good experiences using eclipse-gtk for development.
For small files, the midnight-commander and scite are good editors.
I guess scite isn't included in the distro (as well as eclipse).