After you uncompress the bin file you should move your jdb directory to a more 'logical' place and create a symbolic link to the java binary.
mv Downloads/jdk1.6.0_24 /usr/share
ln -s /usr/share/jdk1.6.0_24/bin/java /usr/bin/java
From that moment on you can call java from any directory in your system if /usr/bin is in your PATH which normally always is. If you install a package using the package manager the binary files are normally installed in /usr/bin on Ubuntu if I'm not mistaking.