Random is shared between all instances of an object

I want to create a bunch of dots and move each of them in a random direction. Problem is that all dots are heading the same direction, so they look like a single dot even if there are a hundred of them. I tried to google it but found nothing. I bet it's just my stupidity, but I really don't know what to do with it. Thanks for helping me.

Dot class:

public class Dot extends JPanel {
    
    private PVector pos;
    private PVector vel;
    private PVector acc;
    
    private Brain brain;
    
    private boolean dead = false;
    
    public Dot(){
        this.brain = new Brain(400);
        
        this.pos = new PVector(Main.width/2, Main.height/2);
        this.vel = new PVector(0, 0);
        this.acc = new PVector(0, 0);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.fillOval((int)pos.x, (int)pos.y, 4, 4);
    }
    
    public void show(JFrame frame) {
        frame.add(this);
    }
    
    public void move() {
        if(brain.directions.length > brain.step) {
            acc = brain.directions[brain.step];
            brain.step++;
        } else {
            dead = true;
        }
        
        vel.add(acc);
        vel.limit(5);
        pos.add(vel);
    }
    
    public void update() {
        if(!dead) {
            move();
            
            if(pos.y < 2 || pos.y < 2 || pos.x > Main.width - 2 || pos.y > Main.height - 2) {
                dead = true;
            }
        }
    }
}

Brain class:

public class Brain {

    public PVector[] directions;
    public int step = 0;
    
    public Brain(int size) {
        directions = new PVector[size];
        randomize();
    }
    
    private void randomize() {
        for(int i = 0; i < directions.length; i++) {
            Random random = new Random();
            float randomAngle = (float)(random.nextFloat() * 2 * Math.PI);
            directions[i] = PVector.fromAngle(randomAngle);
        }
    }
}

Population class:

public class Population {

    public Dot[] dots;
    
    public Population(int size) {
        dots = new Dot[size];
        
        for(int i = 0; i < size; i++) {
            dots[i] = new Dot();
        }
    }
    
    public void show(JFrame frame) {
        for(int i = 0; i < dots.length; i++) {
            dots[i].show(frame);
        }
    }
    
    public void update() {
        for(int i = 0; i < dots.length; i++) {
            dots[i].update();
        }
    }
}

Gui class:

public class Gui {

    JFrame frame = new JFrame();
    
    Population test = new Population(100);
    
    public Gui() {
        startup();
    }
    
    private void startup() {
        frame.setSize(Main.width, Main.height);
        frame.setLocation(200, 200);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
        
        ScheduledExecutorService executor = Executors
                .newSingleThreadScheduledExecutor();
        executor.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                update();
            }
        }, 0, 1000 / 60, TimeUnit.MILLISECONDS);
        
        test.show(frame);
    }
    
    private void update() {
        frame.repaint();
        
        test.update();
    }
}