Creating a User Interface in JavaFX - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 71

/**
* The Y coordinate of the left paddle
*/
DoubleProperty leftPaddleY = new SimpleDoubleProperty();
/**
* The Y coordinate of the right paddle
*/
DoubleProperty rightPaddleY = new SimpleDoubleProperty();
/**
* The drag anchor for left and right paddles
*/
double leftPaddleDragAnchorY;
double rightPaddleDragAnchorY;
/**
* The initial translateY property for the left and right paddles
*/
double initLeftPaddleTranslateY;
double initRightPaddleTranslateY;
/**
* The moving ball
*/
Circle ball;
/**
* The Group containing all of the walls, paddles, and ball. This also
* allows us to requestFocus for KeyEvents on the Group
*/
Group pongComponents;
/**
* The left and right paddles
*/
Rectangle leftPaddle;
Rectangle rightPaddle;
/**
* The walls
*/
Rectangle topWall;
Rectangle rightWall;
Rectangle leftWall;
Rectangle bottomWall;
Button startButton;