Error with random number

Question

There's something wrong with this code and not to sure what, I'm trying to make a random number between 0.8 and 1.2, this can then be used to times the length of the branches that are made using this program.

import java.awt.*;
import javax.swing.*;
import java.util.Random;


public class OneFractalTree extends JApplet {

final double ONE_DEGREE   = Math.PI/180;  
final double BRANCHANGLE  = ONE_DEGREE*30; 
final double SHRINKFACTOR = .65;           
final int    START_LENGTH = 75;            

//Draws branches
public void drawbranch( Graphics g, 
                        double   startx, //coordinates of branch start
                        double   starty, 
                        double   length, //length of branch
                        double   angle   ) //angle of branch
{
    double endx = startx + Math.sin(angle) * length; //Calculates the end coordinates of the branch
    double endy = starty + Math.cos(angle) * length;

    /** 
     * The loop draws the branches and continues until the length becomes too small 
     * i.e. when length is less than 1, length becomes smaller by shrinkfacter every iteration)
     */
    if( 1 < length ) {      

         Random rand = new Random();
         int randomNum = rand.nextInt((12 - 8) + 1) + 1;
         double randomNumdouble = randomNum / 10;



        g.setColor( length < 5 ? Color.green : Color.black ); //Sets color according to length
        g.drawLine( (int)startx, (int)starty, (int)endx, (int)endy ); //Coordinates to draw line
        drawbranch( g, endx, endy, (length * SHRINKFACTOR) * randomNumdouble, angle - BRANCHANGLE ); //1st branch creation
        drawbranch( g, endx, endy, (length * SHRINKFACTOR) * randomNumdouble, angle + BRANCHANGLE ); //2nd branch creation
        drawbranch( g, endx, endy, (length * SHRINKFACTOR) * randomNumdouble, angle); //3rd branch creation
    }
}


public void paint( Graphics g ) {
    Rectangle r = getBounds(); //Finds height of applet viewer
    drawbranch( g, r.width/2, r.height, START_LENGTH, Math.PI );     //Calls method to draw branch
}

}

Answer 1

The correct formula is

Random.nextDouble() * (max - min) + min;

But to fix your code:

int randomNum = rand.nextInt((12 - 8) + 1) + 1;
double randomNumdouble = randomNum / 10.0; // 10 will be interpreted as an `int`, whereas 10.0 will be a `double`