List all installed jre linux

/usr/sbin/update-alternatives --config java

There are 2 programs which provide 'java'. Selection Command ----------------------------------------------- * 1 /usr/lib/jvm/jre-1.4.2-gcj/bin/java + 2 /usr/java/jdk1.6.0_18/bin/java Enter to keep the current selection[+], or type selection number: