Actually, learnmebitcoin helped toooo much in understanding and developing the simple app that I have developed. What would you say about entropy generation ? Would you only use java's SecureRandom ?
I do not know.
If it is for learning purposes, you may use whatever you want if it only gives you fun. You may experiment with different inputs etc.
For serious usage I would stay with secure solutions understanding what they really do. You call java method, but what does it mean? Depending on system it may use Windows or Linux entropy source etc - that subject is really wide and you may read a lot about it.
If you base your program purely on user input, you will receive nothing else than brainwallet generator.