Question: > 
> **Possible Duplicate:**  
> 
> [Interface vs Base class](https://stackoverflow.com/questions/56867/interface-vs-base-class) 
> 
> 
> 

A class implementing an `interface` has to implement all the methods of the interface, `but` if that class is implementing an `abstract class` is it necessary to implement all `abstract methods`?  

**If not**, can we create the `object` of that class which is implementing the `Abstract class`???

Answer: 
> 
> ... but I don't understand licensing issues.
> 
> 
> 

If you are going to build a commercial application on top of someone elses platform or libraries, you *need* to understand the licensing issues, *irrespective* of whether the libraries are open source or closed source. There are no short cuts here. **You** need to do the research, understand the licenses and make your decisions based on that understanding.
Software released under GPL or LGPL might not be what you're looking for, just because it requires that your product will be released under the same license.

Here is an overview of licenses with tons of links to explanations: <http://en.wikipedia.org/wiki/Comparison_of_free_software_licenses>