How to avoid collision with the border or with each other by changing the heading i.e. rotate the object

• The task is actually, two cars moving, the cars must be able to avoid
  collision with the border or with each other by changing the heading
  for example: rotate the object. **
  >I got an error for this
  > getRadius()

   import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import javafx.animation.KeyFrame;
  import javafx.animation.Timeline;
  import javafx.application.Application;
  import javafx.event.ActionEvent;
  import javafx.event.EventHandler;
  import javafx.geometry.Bounds;
  import javafx.scene.Scene;
  import javafx.scene.image.Image;
  import javafx.scene.image.ImageView;
  import javafx.scene.layout.Pane;
  import javafx.scene.paint.Color;
  //import javafx.scene.shape.Circle;
  import javafx.stage.Stage;
  import javafx.util.Duration;
  public class Car extends Application {
  //public static Image car;
  public static Pane canvas;
  @Override
  public void start(final Stage primaryStage) throws FileNotFoundException {
  canvas = new Pane();
  final Scene scene = new Scene(canvas, 800, 600);
  scene.setFill(Color.LIGHTGREEN);
  primaryStage.setTitle("Car");
  primaryStage.setScene(scene);
  primaryStage.show();
  //export image
  Image car1 = new Image(new FileInputStream("src/car2.png"));
  Image car2 = new Image(new FileInputStream("src/car1.png"));
  ImageView c1 = new ImageView(car1);
  ImageView c2 = new ImageView(car2);
  c1.setFitHeight(100);//Resize image
  c1.setFitWidth(100);
  c1.relocate(100,100);
  c2.setFitHeight(100);//Resize image
  c2.setFitWidth(100);
  c2.relocate(600,100);
  c2.setImage(car2);
  c2.setVisible(true);
  //add to stage
  canvas.getChildren().add(c1);
  canvas.getChildren().add(c2);
  final Timeline loop = new Timeline(new KeyFrame(Duration.millis(10), new EventHandler<ActionEvent>() {
  double deltaX = 3;
  double deltaY = 3;
  @Override
  public void handle(final ActionEvent t) {
  c1.setLayoutX(c1.getLayoutX() + deltaX);
  c1.setLayoutY(c1.getLayoutY() + deltaY);
  c2.setLayoutX(c2.getLayoutX() + deltaX);
  c2.setLayoutY(c2.getLayoutY() + deltaY);
  final Bounds bounds = canvas.getBoundsInLocal();
  final boolean atRightBorder = c1.getLayoutX() >= (bounds.getMaxX() - c1.getRadius());
  final boolean atLeftBorder = c1.getLayoutX() <= (bounds.getMinX() + c1.getRadius());
  final boolean atBottomBorder = c1.getLayoutY() >= (bounds.getMaxY() - c1.getRadius());
  final boolean atTopBorder = c1.getLayoutY() <= (bounds.getMinY() + c1.getRadius());
  if (atRightBorder || atLeftBorder) {
  deltaX *= -1;
  }
  if (atBottomBorder || atTopBorder) {
  deltaY *= -1;
  }
  }
  }));
  loop.setCycleCount(Timeline.INDEFINITE);
  loop.play();
  }
  /**
  * @param args the command line arguments
  */
  public static void main(String[] args) {
  launch(args);
  }
  }
  

First thing, get the movement of the two cars fixed, so they stay withing canvas bounds. <br/>

import java.io.FileNotFoundException;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Bounds;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.util.Duration;
public class Car extends Application {
private Pane canvas;
private static final String[] CIRCLES_128 = {
"https://cdn3.iconfinder.com/data/icons/softwaredemo/PNG/128x128/Circle_Green.png",
"https://cdn3.iconfinder.com/data/icons/softwaredemo/PNG/128x128/Circle_Red.png",
};
@Override
public void start(final Stage primaryStage) throws FileNotFoundException {
canvas = new Pane();
final Scene scene = new Scene(canvas, 800, 600);
scene.setFill(Color.LIGHTGREEN);
primaryStage.setTitle("Car");
primaryStage.setScene(scene);
Image car1Image = new Image(CIRCLES_128[0]);
Image car2Image = new Image(CIRCLES_128[1]);
ImageView car1 = new ImageView(car1Image);
ImageView car2 = new ImageView(car2Image);
car1.setFitHeight(100);//Resize image
car1.setFitWidth(100);
car1.relocate(100,100);
car2.setFitHeight(100);//Resize image
car2.setFitWidth(100);
car2.relocate(600,100);
//add to stage
canvas.getChildren().addAll(car1, car2);
final Timeline loop = new Timeline(new KeyFrame(Duration.millis(10), new EventHandler<ActionEvent>() {
double car1DeltaX = 3, car2DeltaX = 3;  //each car must have its own deltaX and Y because
double car1DeltaY = 3, car2DeltaY = 3;  //only one car has to change direction when hitting the edge
@Override
public void handle(final ActionEvent t) {
car1.setLayoutX(car1.getLayoutX() + car1DeltaX);
car1.setLayoutY(car1.getLayoutY() + car1DeltaY);
car2.setLayoutX(car2.getLayoutX() + car2DeltaX);
car2.setLayoutY(car2.getLayoutY() + car2DeltaY);
final Bounds bounds = canvas.getBoundsInLocal();
final Bounds car1Bounds = car1.getBoundsInParent();
final Bounds car2Bounds = car2.getBoundsInParent();
//check car1
final boolean car1AtRightBorder = car1Bounds.getMaxX() >= bounds.getMaxX() ;//- bounds.getRadius();
final boolean car1AtLeftBorder = car1Bounds.getMinX()<= bounds.getMinX() ;//+ car1.getRadius();
final boolean car1AtBottomBorder = car1Bounds.getMaxY() >= bounds.getMaxY() ;//- car1.getRadius();
final boolean car1AtTopBorder = car1Bounds.getMinY()  <= bounds.getMinY() ;//+ car1.getRadius();
if (car1AtRightBorder || car1AtLeftBorder) {
car1DeltaX *= -1;
}
if (car1AtBottomBorder || car1AtTopBorder) {
car1DeltaY *= -1;
}
//check car2
final boolean car2AtRightBorder = car2Bounds.getMaxX() >= bounds.getMaxX() ;
final boolean car2AtLeftBorder = car2Bounds.getMinX()<= bounds.getMinX() ;
final boolean car2AtBottomBorder = car2Bounds.getMaxY() >= bounds.getMaxY() ;
final boolean car2AtTopBorder = car2Bounds.getMinY()  <= bounds.getMinY() ;
if (car2AtRightBorder || car2AtLeftBorder) {
car2DeltaX *= -1;
}
if (car2AtBottomBorder || car2AtTopBorder) {
car2DeltaY *= -1;
}
}
}));
primaryStage.show();
loop.setCycleCount(Timeline.INDEFINITE);
loop.play();
}
static void main(String[] args) {
launch(args);
}
}

Then you can add a simple method to determine if two bounds intersect :

private boolean collisionDetected(Bounds b1, Bounds b2) {
return b1.intersects(b2);
}

and use it in the loop:

   public void handle(final ActionEvent t) {
car1.setLayoutX(car1.getLayoutX() + car1DeltaX);
car1.setLayoutY(car1.getLayoutY() + car1DeltaY);
car2.setLayoutX(car2.getLayoutX() + car2DeltaX);
car2.setLayoutY(car2.getLayoutY() + car2DeltaY);
final Bounds bounds = canvas.getBoundsInLocal();
final Bounds car1Bounds = car1.getBoundsInParent();
final Bounds car2Bounds = car2.getBoundsInParent();
if(collisionDetected(car1Bounds, car2Bounds)){
car1DeltaX *= -1;  car1DeltaY *= -1;
car2DeltaX *= -1;  car2DeltaY *= -1;
}
//check car1
final boolean car1AtRightBorder = car1Bounds.getMaxX() >= bounds.getMaxX() ;
final boolean car1AtLeftBorder = car1Bounds.getMinX()<= bounds.getMinX() ;
final boolean car1AtBottomBorder = car1Bounds.getMaxY() >= bounds.getMaxY() ;
final boolean car1AtTopBorder = car1Bounds.getMinY()  <= bounds.getMinY() ;
if (car1AtRightBorder || car1AtLeftBorder) {
car1DeltaX *= -1;
}
if (car1AtBottomBorder || car1AtTopBorder) {
car1DeltaY *= -1;
}
//check car2
final boolean car2AtRightBorder = car2Bounds.getMaxX() >= bounds.getMaxX() ;
final boolean car2AtLeftBorder = car2Bounds.getMinX()<= bounds.getMinX() ;
final boolean car2AtBottomBorder = car2Bounds.getMaxY() >= bounds.getMaxY() ;
final boolean car2AtTopBorder = car2Bounds.getMinY()  <= bounds.getMinY() ;
if (car2AtRightBorder || car2AtLeftBorder) {
car2DeltaX *= -1;
}
if (car2AtBottomBorder || car2AtTopBorder) {
car2DeltaY *= -1;
}
}
}));

<hr>

<hr>
The following is a refactored cleaner version:

public class Car extends Application {
private Pane canvas;
private static final String[] CIRCLES_128 = {
"https://cdn3.iconfinder.com/data/icons/softwaredemo/PNG/128x128/Circle_Green.png",
"https://cdn3.iconfinder.com/data/icons/softwaredemo/PNG/128x128/Circle_Red.png",
};
private double car1DeltaX = 3, car2DeltaX = 3;  //each car must have its own deltaX and Y because
private double car1DeltaY = 3, car2DeltaY = 3;  //only one car has to change direction when hitting the edge
@Override
public void start(final Stage primaryStage) throws FileNotFoundException {
canvas = new Pane();
final Scene scene = new Scene(canvas, 800, 600);
scene.setFill(Color.LIGHTGREEN);
primaryStage.setTitle("Car");
primaryStage.setScene(scene);
Image car1Image = new Image(CIRCLES_128[0]);
Image car2Image = new Image(CIRCLES_128[1]);
ImageView car1 = new ImageView(car1Image);
ImageView car2 = new ImageView(car2Image);
car1.setFitHeight(100);//Resize image
car1.setFitWidth(100);
car1.relocate(100,100);
car2.setFitHeight(100);//Resize image
car2.setFitWidth(100);
car2.relocate(600,100);
//add to stage
canvas.getChildren().addAll(car1, car2);
final Timeline loop = new Timeline(new KeyFrame(Duration.millis(10), t -> {
//move 2 cars to new position
positionNode(car1, car1DeltaX, car1DeltaY);
positionNode(car2, car2DeltaX, car2DeltaY);
final Bounds canvasBounds = canvas.getBoundsInLocal();
final Bounds car1Bounds = car1.getBoundsInParent();
final Bounds car2Bounds = car2.getBoundsInParent();
if(collisionDetected(car1Bounds, car2Bounds)){
handleCollision();
}
//check car1 within canvas bounds
if(atHorizontalEdge(canvasBounds,car1Bounds)){
car1DeltaX *= -1;
}
if(atVerticalEdge(canvasBounds,car1Bounds)){
car1DeltaY *= -1;
}
//check car2 within canvas bounds
if(atHorizontalEdge(canvasBounds,car2Bounds)){
car2DeltaX *= -1;
}
if(atVerticalEdge(canvasBounds,car2Bounds)){
car2DeltaY *= -1;
}
}));
primaryStage.show();
loop.setCycleCount(Timeline.INDEFINITE);
loop.play();
}
private void positionNode(Node node, double deltaX, double deltaY) {
node.setLayoutX(node.getLayoutX() + deltaX);
node.setLayoutY(node.getLayoutY() + deltaY);
}
private boolean collisionDetected(Bounds b1, Bounds b2) {
return b1.intersects(b2);
}
private boolean atHorizontalEdge(Bounds enclosing, Bounds enclosed) {  
return enclosed.getMaxX() >= enclosing.getMaxX() || enclosed.getMinX()<= enclosing.getMinX() ;
}
private boolean atVerticalEdge(Bounds enclosing, Bounds enclosed) {  
return enclosed.getMaxY() >= enclosing.getMaxY() || enclosed.getMinY()<= enclosing.getMinY() ;
}
private void handleCollision() {
//change cars directions
car1DeltaX *= -1;  car1DeltaY *= -1;
car2DeltaX *= -1;  car2DeltaY *= -1;
}
public static void main(String[] args) {
launch(args);
}
}