sudo update-alternatives --config java will produce:

Selection Path           Priority Status

---

0 /usr/lib/jvm/java-7-openjdk-i386/jre/bin/java 1071 auto mode

*1 /usr/lib/jvm/java-6-openjdk-i386/jre/bin/java 1061 manual mode

2 /usr/lib/jvm/java-7-openjdk-i386/jre/bin/java 1071 manual mode

The you can select a number to specify the default JDK;

use sudo update-alternatives --config javac config javac version.