How to do the "stars" at random location and size using Math.random()*MAX?

Question

Im just starting Java course and professor have asked us to fill out the window with small circles making it look like stars. We need to use Math.random()*MAX to set the random amount and size with a given limit.

Java Screenshot

I have been trying different things but I feel so lost with Java. I have also look for examples online but they are all about random numbers.

gc.fillRect(0, 0, 400, 400);

gc.setFill(Color.WHITE);

    gc.fillOval(50, 60, 2, 2);
    gc.fillOval(150, 200, 2, 2);
    gc.fillOval(150, 100, 3, 3);
    gc.fillOval(230, 220, 3, 3);
    gc.fillOval(80, 200, 2, 2);
    gc.fillOval(350, 200, 2, 2);
    gc.fillOval(300, 250, 2, 2);
    gc.fillOval(320, 350, 2, 2);
    gc.fillOval(20, 320, 2, 2);

Instead of having all this lines repeat with different values I believe the Math.random is supposed to do it but im not sure how to use it properly, or how to implement it properly to my problem. Any example or guidance is more than welcome.

[This](https://stackoverflow.com/questions/59014258/adding-randomly-generated-circles-of-uniform-size-in-a-scene-to-represent-star/59015888#59015888) uses nodes and not `Canvas`. Hopefully the ideas are helpful. — SedJ601, Jan 21 '23 at 05:37
_I believe the Math.random is supposed to do it but im not sure how to use it properly_ then you have to do some research: study your coursebook, the api doc, external tutorials .. anyway, using random is basic java unrelated to javafx — kleopatra, Jan 21 '23 at 10:41
Example [random circle tutorial](https://docs.oracle.com/javafx/2/get_started/animation.htm), though it does more stuff and is more complex than what you need, it is pretty. — jewelsea, Jan 21 '23 at 12:39

score 4 · Answer 1 · answered Jan 21 '23 at 07:08

Math.random() is pretty straight forward.

int nrOfStars = 20; // you choose your parameters
int maxSizeX = 400;
int maxSizeY = 400;
int maxWidth = 10;
int maxHeight = 10;

int posX;
int posY;
int width;
int height;

gc.fillRect(0, 0, maxSizeX, maxSizeY);
gc.setFill(Color.WHITE);

for (int i = 0; i < nrOfStars; i++) {
  posX = (int) (Math.random() * maxSizeX);
  posY = (int) (Math.random() * maxSizeY);
  width = (int) (Math.random() * maxWidth);
  height = (int) (Math.random() * maxHeight);
  System.out.println(
      "x: " + posX + " | y: " + posY + " | height: " + width + " | height " + height);
}

Although I do recoment you youse nextInt() like:

Random r = new Random();
// for...
posX = r.nextInt(maxSizeX);
posY = r.nextInt(maxSizeY);
width = r.nextInt(maxWidth);
height = r.nextInt(maxHeight);

Giovanni Contreras · Answer 2 · 2023-01-21T06:03:49.047

2

You can set a pane as parent of the circle shapes . E.g. pane 400 width and 300 heigth . Those are the maxinum random number to translate in x and y axis . Also you can set radius of circles at random number e.g. 5 as max random number . You can make a for loop and make a new circle instance with those random number as arguments in circle`s constructor in each iteration and add it as child of pane

edited Jan 21 '23 at 06:03

answered Jan 21 '23 at 05:53

Giovanni Contreras

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1
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score 1 · Answer 3 · answered Jan 21 '23 at 16:01

In this example circles are made in a loop and add it to pane's children. circles are evenly distributed . It's up to you make it at random positions :). Check this ramdom.nexInt() tutorial

App.java

public class App extends Application {

    @Override
    public void start(Stage stage) {
        // pane as root of scene
        Pane pane = new Pane();
        // pane background black
        pane.setStyle("-fx-background-color:black;");

        // loop to make new circles and add it  as pane's children 
        for (int i = 1; i < 20; i++) {
            for (int j = 1; j < 15; j++) {
                Circle circle = new Circle(20 * i, 20 * j, 5, Color.WHITE);
                pane.getChildren().add(circle);
            }

        }
        var scene = new Scene(pane, 400, 300);

        stage.setScene(scene);
        stage.show();
    }

    public static void main(String[] args) {
        launch();
    }

}

result :

How to do the "stars" at random location and size using Math.random()*MAX?

3 Answers3