This is for a 64bit system:
Download Oracle’s JDK7 RPM package for 64bit Linux. The filename should be “jdk-7-linux-x64.rpm”.

Then as root:

zypper install jdk-7-linux-x64.rpm
cd /usr/java/jdk1.7.0/bin
for bin in *; do update-alternatives --install /usr/bin/$bin $bin $(pwd)/$bin 20000; done