I would like to ask a few questions about software licenses, with regards to a (Java) program I am making. I am very very new to licenses, so please bear with me.
1. If I produce a Java program using 'internal' libraries (such as JavaFX), am I allowed to sell my program? Do I need to include (distribute) my source code?
2. If I produce a Java program using 'external' libraries (in addition to 'internal ones') which are licensed under the GPL license, am I able to sell my program? Do I need to include (distribute) my source code OR the external library source OR both?
3. Does selling a program which makes use of GPL licensed 'external' library, give the purchaser the option of reselling and charging any price ($0.00-$infinite), (and making potentially infinite, copies of) my program?
4. Are there any other notable constraints that using a external library (licensed under this GPL license) in my program, will incur?