Bouncy Balls

Functional Specifications

The user will be presented with a window having a play button, which needs to be clicked to start the game. There will also be an input textfield to enter the number of balls to start with.
The user can have a look at the help/info instructions before starting the game.
If the user puts an invalid entry into the text field which is not an integer the game will start with the default of 50 balls.
The user is only allowed to fill the space with up to 1000 balls in the start. If the user puts more than that in the text field the balls will be set to 1000.
When the user enters the starting number of balls in the text field, the user needs to press the enter button and click the play button. When the user hits the play button the screen is presented with balls of different sizes and velocities moving around and a counter on top to display the number of balls.
The user can also add more balls and remove balls from the screen using the add and subtract buttons. The maximum amount of balls in the screen can be 1050 (1000 max in the start and then the user can add 50 more).
The user can stop and restart the game by pressing the pause button.
The text field on the start screen gets replaced by the count of the balls, add and subtract buttons when the user presses the play button.
The default number of balls on the screen is 50.
The background of the balls panel changes to black on mouse over and changes back to white on mouse exit, while playing the game.