In theory, you can run "make install" on a newly built JDK to have it installed in /usr/local/bin, just as with many system tools.

This is not recommended to do. You might mess up your boot JDK, and Java installations generally do not work like this. (Instead, you are likely to have symbolic links to e.g. bin/java, bin/javac etc in a JDK home.)

This code is not only old and untested, I also think it offers the user a very unwise move. It should be removed.