Problems with Constructors and Drawing a Car

[Mathew Dodge]

Hello All,

I was attempting to write a code which would create a car class. Then display two cars on a screen. The problem is I keep getting a couple errors.
It seems that the car constructor is not being created before the CarComponent class creates the object. But I don't really know what to do..... Thanks!

___________________________________

import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;

public class CarComponent extends JComponent
{
   public void paintComponent(Graphics g)
   {
      Graphics2D g2 = (Graphics2D) g;
      
      Car car1 = new Car(0, 0);
      
      int x = this.getWidth() - 60;
      int y = this.getHeight() - 30;
      
      Car car2 = new Car(x, y);
      
      car1.draw(g2);
      car2.draw(g2);
   }
}
__________________________________________

import javax.swing.JFrame;

public class CarViewer 
{
   public static void main(String[] args)
   {
      JFrame frame = new JFrame();
      
      frame.setSize(300, 400);
      frame.setTitle("Two Cars");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      
      CarComponent component = new CarComponent();
      frame.add(component);
      
      frame.setVisible(true);
   }
}
______________________________________________

import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JComponent;

/**
   A car shape that can be positioned anywhere on the screen.
*/
public class Car 
{
   private int xLeft;
   private int yTop;
   
   /**
      Constructs a car with a given top left corner.
      @param x the x coordinate of the top left corner
      @param y the y coordinate of the top left corner
   */
   public car(int x, int y)
   {
      xLeft = x;
      yTop = y;
   }
   
   /**
      Draws the car.
      @param g2 the graphics context
   */
   public void draw(Graphics2D g2)
   {
      Rectangle body = new Rectangle(xLeft, yTop + 10, 60, 10);
      Ellipse2D.Double frontTire = new Ellipse2D.Double(xLeft + 10, yTop + 20, 10, 10);
      Ellipse2D.Double rearTire = new Ellipse2D.Double(xLeft + 40, yTop + 20, 10, 10);
      
      // The Bottom of the front windshield
      Point2D.Double r1 = new Point2D.Double(xLeft + 10, yTop + 10);
      
      // The front of the roof
      Point2D.Double r2 = new Point2D.Double(xLeft + 20, yTop);
      
      // The rear of the roof
      Point2D.Double r3 = new Point2D.Double(xLeft + 40, yTop);
      
      // The bottom of the rear windshield
      Point2D.Double r4 = new Point2D.Double(xLeft + 50, yTop + 10);
      
      Line2D.Double frontWindshield = new Line2D.Double(r1, r2);
      Line2D.Double roofTop = new Line2D.Double(r2, r3);
      Line2D.Double rearWindshield = new Line2D.Double(r3, r4);
      
      g2.draw(body);
      g2.draw(frontTire);
      g2.draw(rearTire);
      g2.draw(frontWindshield);
      g2.draw(roofTop);
      g2.draw(rearWindshield);
      
   }
}

_________________________________________________________

[Greg Charles]

Hi Mathew, welcome to Java Ranch!

First, please use code tags when posting code samples. They make the code much easier to read. I've added them for you above.

Now, what kind of errors are you getting? Compile errors, run time exceptions, wrong behavior? On a quick scan, I see you defined your Car class with a capital C, but you've written the constructor with a lowercase c. The constructor name has to match the class name exactly, even the case. That mismatch will cause a compile error. If it still doesn't compile after you fix that, post the messages the compiler gives you and we'll try to figure it out together.

[Darryl Burke]

In addition to what Greg said, don't construct new Cars in the paintComponent(...) override. Painting methods are for painting, and painting alone. You have absolutely no control over how often or how many times that method will be called.

[Mathew Dodge]

Thanks to both of you! You're more helpful than my programming professor.... It was the lower case letter in the car constructor which was causing the error. That was something that I just wouldn't have seen! Thank you both again!