How to Draw a Diamond in Java

Although Java does not include any default methods for drawing a diamond, it is relatively easy to create one yourself. This method will take a x coordinate and a y coordinate that mark the upper-left corner of the rectangle that encompasses your diamond. For example, if the y coordinate of the highest point on the diamond is 50 and the x coordinate of the leftmost point on the diamond is 25, the bounding coordinates will be 25 and 50. The method will also take a value for the height of the diamond and a value for the width of the diamond.

Instructions

Create a JFrame to Draw On

1. Start a new project in the Integrated Development Environment, or IDE, that you are most experienced with.

2. Create a new class called "DrawingComponent" in your project. Type "extends Component" immediately after "DrawingComponent" but before the opening bracket at the end of the class declaration.

3. Type the following code above the DrawingComponent class's declaration to import the required files into the class:
   import java.awt.Component;
   import java.awt.Graphics;
   import java.awt.Graphics2D;
   import java.awt.geom.GeneralPath;

4. Add a new paint method to override the component's default paint method. Insert the following code between the opening and closing brackets of the DrawingComponent class:
   public void paint(Graphics g) {

   }

5. Create a new JFrame in your project's main method and add your custom drawing component to it with this code:
   javax.swing.JFrame frame = new javax.swing.JFrame();
   int frameWidth = 300;
   int frameHeight = 300;
   frame.setSize(frameWidth, frameHeight);
   frame.setVisible(true);
   frame.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
   frame.getContentPane().add(new DrawingComponent());

Draw a Diamond

1. Create a new method in the DrawingComponent class by adding this code between the class's opening and closing brackets, but outside of the other methods in the class:
   GeneralPath createDiamond(int x, int y, int width, int height){

   }

2. Enter the following code inside the createDiamond method to define a new GeneralPath with four lines:
   GeneralPath diamond = new GeneralPath(GeneralPath.WIND_EVEN_ODD,4);

3. Calculate the four points of the diamond given the values passed into the method. Each time you calculate a point, guide the path through that point. Use the following code to accomplish this:
   x+=width/2;
   diamond.moveTo(x, y);
   x+=width/2;
   y+=height/2;
   diamond.lineTo(x,y);
   x-=width/2;
   y+=height/2;
   diamond.lineTo(x,y);
   x-=width/2;
   y-=height/2;
   diamond.lineTo(x,y);

4. Close the GeneralPath object to turn it into a completed diamond and then return it with this code:
   diamond.closePath();
   return diamond;

5. Call the createDiamond method inside of the paint method and pass the result to an instance of Graphics2D to draw the diamond with the following code:
   Graphics2D g2d = (Graphics2D) g;
   g2d.draw(createDiamond(100,100,50,100));

References

• Oracle: Drawing Arbitrary Shapes
• John Hopkins University; Java2D An Introduction and Tutorial