Assuming you installed the OpenJDK6 with:
sudo apt-get install openjdk-6-jdk
In Ubuntu 64 bit, make sure the paths are valid for your installation (change if using 32bit version):
/usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java
/usr/lib/jvm/java-6-openjdk-amd64/bin/javac
Setup update-alternatives:
sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java" 1
sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/java-6-openjdk-amd64/bin/javac" 1
sudo update-alternatives --set java /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java
sudo update-alternatives --set javac /usr/lib/jvm/java-6-openjdk-amd64/bin/javac
Alternatively, make sure the correct version is checked for both Java and compiler:
sudo update-alternatives --config java
sudo update-alternatives --config javac
List the installed Java alternatives with:
sudo update-alternatives --list java
sudo update-alternatives --list javac
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