Re: grasp difference between using and reimplementing API ?
There is obviously a difference, but there have been many implementations of the Java API and android was based on one of them, Harmony. The only time licensing has ever been an issue with anyone but Google was when someone released an implementation and using the Java name without passing Suns/Oracles Java TCK (Technology Compatibility Kit) process.
Microsoft fell foul of this when they shipped their own non compliant Java branded runtime. Android's only Java aspect is the programming language. Where are the lawsuits against GCJ, IcedTea or even Harmony.
It has been mentioned elsewhere on here Sun encouraged Java to be re-implemented which involves implementing the API. In a sane world where law makes sense the only potential issue would be around copying code that actually implements the API. If you go through the code that Oracle brought to the table in the first round of this, it were demonstrated to be test code inadvertently committed by a sub contractor or just so trivial that even the Judge stated that is the only sensible it could have been written (rangeCheck).