Drawing image only once, without repainting

Question

I have written simple animation in java, with paintComponent(Graphics g) method being called all over again.

The problem is, the painting I draw in the background is generated randomly. So every time the repaint() is called, it changes.

It's generated by drawing rectangles, so I need graphics handler there.

How can I solve this problem?

public void paintComponent(Graphics g)
{
   landscape = new Landscape(g); // landscape - attribute

   //...
}

So the constructor is called a lot of times:

public class Landscape 
{

    public Landscape(Graphics g)
    {
        Graphics2D g2d = (Graphics2D)g;

        g2d.setColor(new Color(92, 163, 99));

        Random rand = new Random();
        int first = rand.nextInt((800 - 1) + 1) + 1;
        g2d.fillRect(0, 800 - first, 1, first);

        int d = first % 2;
        if(d == 0) d = -1;

        for(int i = 1; i <= 800; i++) {
            int choose = rand.nextInt((1000 - 1) + 1) + 1;

            if(choose > 950) {
                d = -(d);
            }

            if(d == -1) {
                first += 1;                
            } else {
                first -= 1;
            }

            g2d.fillRect(i, 800 - first, 1, first);
        }
    }

} // End Landscape

And everytime all points change.

Answer 1

Separate the construction of the rectangles from the drawing of the rectangles.

You construct the rectangles in the constructor and draw the rectangles in the draw method.

Here's your Landscape class, rearranged.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Landscape {

    List<Rectangle> rectangles;

    public Landscape() {
        rectangles = new ArrayList<Rectangle>();

        Random rand = new Random();
        int first = rand.nextInt((800 - 1) + 1) + 1;
        rectangles.add(new Rectangle(0, 800 - first, 1, first));

        int d = first % 2;
        if (d == 0)
            d = -1;

        for (int i = 1; i <= 800; i++) {
            int choose = rand.nextInt((1000 - 1) + 1) + 1;

            if (choose > 950) {
                d = -(d);
            }

            if (d == -1) {
                first += 1;
            } else {
                first -= 1;
            }

            rectangles.add(new Rectangle(i, 800 - first, 1, first));
        }
    }

    public void draw(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(new Color(92, 163, 99));
        for (Rectangle r : rectangles) {
            g2d.fillRect(r.x, r.y, r.width, r.height);
        }
    }

} // End Landscape