Little demo of detecting collisions with shapes

MainFrame.java

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.geom.Ellipse2D;

public class MainFrame extends JFrame implements MouseListener {
    private int x;
    private int y;

    public static void main(String[] args) {
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

        MainFrame mainFrame = new MainFrame();

        mainFrame.x = screenSize.width/2 - 50;
        mainFrame.y = screenSize.height/2 - 50;

        mainFrame.setSize(screenSize.width, screenSize.height);
        mainFrame.setVisible(true);

        mainFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        mainFrame.addMouseListener(mainFrame);
    }

    @Override
    public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;

        g2.setColor(Color.BLACK);
        g2.fillRect(0,0, this.getWidth(), this.getHeight());

        Shape circle = new Ellipse2D.Double(x,y,100,100);
        Shape house = drawHouse(500, 500, 50);

        if (circle.intersects(house.getBounds())) {
            g2.setColor(Color.RED);
            g2.fill(circle);
        }

        g2.setColor(Color.WHITE);
        g2.draw(circle);

        g2.setColor(Color.RED);
        g2.draw(house);
    }

    private Shape drawHouse(int x, int y, int wallLength) {
        int bottomLeftX = x - wallLength /2;
        int bottomLeftY = y + wallLength /2;

        Polygon house = new Polygon();

        house.addPoint(bottomLeftX, bottomLeftY);
        house.addPoint(bottomLeftX + 50, bottomLeftY);
        house.addPoint(bottomLeftX + wallLength, bottomLeftY - wallLength);
        house.addPoint(bottomLeftX + wallLength /2, bottomLeftY - wallLength - wallLength /2);
        house.addPoint(bottomLeftX, bottomLeftY - wallLength);
        house.addPoint(bottomLeftX, bottomLeftY);

        return house;
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        this.x = e.getX() - 50;
        this.y = e.getY() - 50;

        this.repaint();
    }

    @Override
    public void mousePressed(MouseEvent e) {}
    @Override
    public void mouseReleased(MouseEvent e) {}
    @Override
    public void mouseEntered(MouseEvent e) {}
    @Override
    public void mouseExited(MouseEvent e) {}
}