How to set or change the default Java (JDK) version on OS X?

Question

How can you change the default version of Java on a mac?

Answer 1

From the Apple's official java_home(1) man page:

**USAGE**

   /usr/libexec/java_home  helps  users  set a $JAVA_HOME in their login rc files, or provides a way for
   command-line Java tools to use the most appropriate JVM which can satisfy a minimum version or archi-
   tecture  requirement.  The --exec argument can invoke tools in the selected $JAVA_HOME/bin directory,
   which is useful for starting Java command-line tools from launchd plists without hardcoding the  full
   path to the Java command-line tool.

   Usage for bash-style shells:
          $ export JAVA_HOME=`/usr/libexec/java_home`

   Usage for csh-style shells:
          % setenv JAVA_HOME `/usr/libexec/java_home`