Draw a tree

package iTest;

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

public class CayleyTree extends JFrame
{
public static void main( String []args ){
CayleyTree frm = new CayleyTree("CayleyTree");
frm.setVisible( true );
SwingUtilities.invokeLater(()->{
frm.init();
frm.drawTree( 10, 200, 400, 100, -Math.PI/2 );
});
}
private Frame frm;
private Graphics graphics;
private int width;
private int height;
private final double PI = Math.PI;
private final double th1 = 30 * PI / 180;
private final double th2 = 20 * PI / 180;
private final double per1 = 0.6;
private final double per2 = 0.7;

public CayleyTree(String title){
super(title);
setSize( 400, 440 );
setBackground( Color.lightGray );
setDefaultCloseOperation(EXIT_ON_CLOSE);
}

public void init(){
width = getSize().width;
height = getSize().height;
graphics = this.getGraphics();
}



void drawTree(int n,
double x0, double y0, double leng, double th)
{
if( n==0 ) return;

double x1 = x0 + leng * Math.cos(th);
double y1 = y0 + leng * Math.sin(th);

drawLine(x0, y0, x1, y1);

drawTree( n - 1, x1, y1, per1 * leng, th + th1 );
drawTree( n - 1, x1, y1, per2 * leng, th - th2 );
}
void drawLine( double x0, double y0, double x1, double y1 ){
graphics.drawLine( (int)x0, (int)y0, (int)x1, (int)y1 );
}

}