How can I get my screen to not flash when Im calling the repain(); function

[obsidian gale]

I'm working on a school project right now and we were tasked with making a program that spawns a shape when you click the screen, the shape will then move in a random direction and bounce all over the place.

I have an issue right now where when I spawn the shape, the screen flashes which I assume is happening because I am repainting the screen every 200ms

[misty fog]

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[obsidian gale]

this.addMouseListener(new java.awt.event.MouseAdapter() {
            @Override
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                // Get mouse position
                int x = evt.getX();
                int y = evt.getY();
                String randomColor = Randomizer.getRandomColor();
                int randomSpeed = Randomizer.getRandomNumber(1, 10);
                int randomWidth = Randomizer.getRandomNumber(10, 100);
                int randomHeight = Randomizer.getRandomNumber(10, 100);
                int randomNumber = Randomizer.getRandomNumber(10, 100);


                int randomNum = Randomizer.getRandomNumber(1,3);
                Shape newShape = null;

                switch(randomNum){
                    case 1:
                        newShape = new Square(x, y, randomWidth, randomHeight, randomSpeed, randomColor);
                        break;
                    case 2:
                        newShape = new Triangle(x, y, randomWidth, randomHeight, randomSpeed, randomColor);
                        break;
                    case 3:
                        newShape = new Circle(x, y, randomWidth, randomHeight, randomSpeed, randomColor);
                        break;
                }
                shapes.add(newShape);








            }
        });

    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2 = (Graphics2D) g;
        for (Shape shape : shapes) {
            shape.draw(g2);
        }
    }

    // Timer to move the shapes
    public void startTimer() {
        Timer timer = new Timer(200, e -> {
            System.out.println("Timer");
            for (Shape shape : shapes) {
                shape.move();
            }
            repaint();
        });
        timer.start();
    }

[sly otter]

is this inside a JFrame or JPanel ?

[obsidian gale]

JFrame, sorry I should have included that

[sly otter]

does this persist if you instead of a JFrame use a JPanel ?

[obsidian gale]

let me take a look here

[obsidian gale]

sorry not the best at java here. When I make it extend JPanel instead of JFrame it doesnt let me run it as a window, so I make a JFrame to put the panel inside of. But that isnt working the panel just doesnt show up

idk if that makes any sense

package classes;
import javax.swing.*;
import java.awt.*;

public class ProgramWindow extends JFrame{
    public ProgramWindow() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(800, 600);
        this.setResizable(false);
        this.setVisible(true);

        //Make our own JPanel
        DrawingPanel drawing = new DrawingPanel();
        drawing.setBackground(Color.RED);

        this.add(drawing );
        drawing.setLayout(null);
    }
}

[sly otter]

public class ProgramWindow extends JFrame{
    public ProgramWindow() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(800, 600);
        this.setResizable(false);
        this.setLayout(new BorderLayout());

        //Make our own JPanel
        DrawingPanel drawing = new DrawingPanel();
        drawing.setBackground(Color.RED);

        this.add(drawing,BorderLayout.CENTER);
        drawing.setLayout(null);
        this.setVisible(true);
    }
}

[obsidian gale]

that works, do you think you can tell me exactly what I did wrong so I know for next time!

And that also fixes my flashing problem 🙂

Like I see you added a border Layout but what does that do specifically?

[sly otter]

are you still overriding paint in the JPanel ?

[obsidian gale]

I changed it from paint and made it paintComponent

but yes

i am overiding it

[sly otter]

yeah that's what I would expect.

[obsidian gale]

@Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        for (Shape shape : shapes) {
            shape.draw(g2);
        }
    }

[sly otter]

A LayoutManager does the job of resizing the components that have been added to them. In our case BorderLayout divides the frame into 5 compartments. NORTH, EAST, SOUTH, WEST, CENTER. I am adding to center because then the component gets stretched to fit the entire window and resizing as well as collisions with other elements registered to this layout manager are taken care of.

[obsidian gale]

thats awesome, okay thank you very much! i wish i could upvote you some how cause you rrly saved me a lot of struggles

[misty fog]

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[obsidian gale]

thank you very much im closing the post now!