Solution 1 (by Petr Prikryl)

Bug#560044: net.ipv6.bindv6only=1 breaks java networking
http://www.mail-archive.com/debian-qa-packages@lists.debian.org/msg30468.html

Netbase has recently introduced the sysctl-setting
net.ipv6.bindv6only=1 in /etc/sysctl.d/bindv6only.conf and this setting
will probably be the default in squeeze.

This setting breaks networking in java, and any traffic will always
result in a „java.net.SocketException: Network is unreachable“.

It should probably be an rc-bug, but setting as important for now, since
users can easily rectify the issue.

Quick fix for users hit by this:

sudo sed -i 's/net.ipv6.bindv6only\ =\ 1/net.ipv6.bindv6only\ =\ 0/' \
/etc/sysctl.d/bindv6only.conf && sudo invoke-rc.d procps restart

Solution 2 (by Tonda Míšek)

Add line to sqldeveloper.conf:

AddVMOption -Djava.net.preferIPv4Stack=true