What is the difference between openjdk-7-jre-headless and openjdk-7-jre(jdk)?

When I type for **java -version** in command prompt in ubuntu I get following output The program 'java' can be found in the following packages: * default-jre * gcj-4.8-jre-headless * openjdk-7-jre-headless * gcj-4.6-jre-headless * openjdk-6-jre-headless Try: apt-get install <selected package> I get above output as I do not have java install. I want to know difference between **openjdk-7-jre-headless** and **openjdk-7-jre**