Why is the output wrong

Question

I should be getting a tree. But I am not getting a tree. I am getting a long thing, not a tree.

This is my code:

Main.java

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Main extends JFrame {

private static final long serialVersionUID = 1L;

public Main() {

    setTitle("Tree");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    //setResizable(false);

    add(new TreeDrawer(), BorderLayout.CENTER);
    getContentPane().setBackground(Color.BLACK);

    //button shit
    JButton generate = new JButton("Generate");
    generate.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {

            TreeDrawer.generate();
            repaint();
        }
    });

    add(generate, BorderLayout.SOUTH);
    pack();
    setVisible(true);

}

public static void main(String[] args) {

    SwingUtilities.invokeLater(() -> {
        new Main();
    });

    }

}

TreeDrawer.java

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.AffineTransform;

import javax.swing.JComponent;

public class TreeDrawer extends JComponent {

private static final long serialVersionUID = 1L;

public static final int ROOM_WIDTH = 1080;
public static final int ROOM_HEIGHT = 720 - 47;// 47 is the height of menu bar on top of jframe or some shit
static double len = 100; the length of each branch shit

public TreeDrawer() {
    setPreferredSize(new Dimension(ROOM_WIDTH, ROOM_HEIGHT));
}

private static String axiom = "F";
private static String sentence = axiom;

private static Graphics2D graphics;

//this shit will change on vary of l system, new rules and etc
private static String rules(char a) {
    if(a == 'F')//a rule
        return "FF+[+F-F-F]-[-F+F+F]";
    return "";//if nothing else works, shit
}

//generates the whole shit
    //probably correct
public static void generate() {
    len *= 0.5;//shrink the shit
    String nextSentence = "";
    for(int i = 0; i < sentence.length(); i++) {
        char current = sentence.charAt(i);
        nextSentence += rules(current);
    }
    sentence = nextSentence;
    System.out.println(sentence);
    turtle();
}

public static void turtle() {

    AffineTransform transform = null;//so you can save shit

    for(int i = 0; i < sentence.length(); i++) {
        char current = sentence.charAt(i);

        if(current == 'F') {//draw up
            graphics.drawLine(0, 0, 0, (int) -len);
            graphics.translate(0, -len);
        }

        else if(current == '+') {//right turn
            graphics.rotate(Math.PI / 6);
        }

        else if(current == '-') {//left turn
            graphics.rotate(-Math.PI / 6);
        }
        //probably wrong shit
        else if(current == '[') {//save transformations

            transform = graphics.getTransform();
        }
        //also probably wrong shit
        else if(current == ']') {//restore from last save
            graphics.setTransform(transform);
        }
    }
}

@Override
public void paintComponent(Graphics g) {//so that shit is drawn
    graphics = (Graphics2D) g;
    graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    super.paintComponent(graphics);
    graphics.translate(ROOM_WIDTH / 2, ROOM_HEIGHT - 10);
    graphics.setPaint(Color.WHITE);

    turtle();

}
}

What did I do wrong. I can not figure out how to post a screenshot of the output that I got, but it looks completely off of what is correct. I know that my algorithm of the L-system is right, because that is working well. But I think that when I try to save and restore the transformation state, something goes wrong. Saving the transformation state is the brackets ([ and ]. '[' saves, ']' restores from that save). But I do not know what is wrong. I need help to find what is wrong. Thank you.

Answer 1

Observations...

1. If you didn't create the instance of Graphics, you should not maintain a reference to it for any longer than you need to use it. Instead, you should pass it as a parameter to the methods that need to use it. This will save you from some serious weird artefacts and possible NullPointerExceptions
2. If you are going to transform the Graphics context, you'd best to create a copy of it before you do, as it's a shared resource between all components getting painted.
3. In this context, static is NOT your friend and is poor design.

Taking all that into account, something like the following works...at a basic level

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Main extends JFrame {

    private static final long serialVersionUID = 1L;

    private TreeDrawer treeDrawer;

    public Main() {

        setTitle("Tree");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        //setResizable(false);

        treeDrawer = new TreeDrawer();
        add(treeDrawer, BorderLayout.CENTER);
        getContentPane().setBackground(Color.BLACK);

        //button shit
        JButton generate = new JButton("Generate");
        generate.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                treeDrawer.generate();
                repaint();
            }
        });

        add(generate, BorderLayout.SOUTH);
        pack();
        setVisible(true);

    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(() -> {
            new Main();
        });

    }

    public class TreeDrawer extends JComponent {

        private static final long serialVersionUID = 1L;

        public static final int ROOM_WIDTH = 1080;
        public static final int ROOM_HEIGHT = 720 - 47;// 47 is the height of menu bar on top of jframe or some shit
        double len = 100;

        public TreeDrawer() {
            setPreferredSize(new Dimension(ROOM_WIDTH, ROOM_HEIGHT));
        }

        private String axiom = "F";
        private String sentence = axiom;

        private String rules(char a) {
            if (a == 'F')//a rule
            {
                return "FF+[+F-F-F]-[-F+F+F]";
            }
            return "";//if nothing else works, shit
        }

        //probably correct
        public void generate() {
            len *= 0.5;//shrink the shit
            String nextSentence = "";
            for (int i = 0; i < sentence.length(); i++) {
                char current = sentence.charAt(i);
                nextSentence += rules(current);
            }
            sentence = nextSentence;
            System.out.println(sentence);
//            turtle();
        }

        public void turtle(Graphics2D graphics) {

            AffineTransform transform = null;//so you can save shit

            for (int i = 0; i < sentence.length(); i++) {
                char current = sentence.charAt(i);

                if (current == 'F') {//draw up
                    graphics.drawLine(0, 0, 0, (int) -len);
                    graphics.translate(0, -len);
                } else if (current == '+') {//right turn
                    graphics.rotate(Math.PI / 6);
                } else if (current == '-') {//left turn
                    graphics.rotate(-Math.PI / 6);
                } //probably wrong shit
                else if (current == '[') {//save transformations

                    transform = graphics.getTransform();
                } //also probably wrong shit
                else if (current == ']') {//restore from last save
                    graphics.setTransform(transform);
                }
            }
        }

        @Override
        public void paintComponent(Graphics g) {//so that shit is drawn
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            super.paintComponent(g2d);
            g2d.translate(ROOM_WIDTH / 2, ROOM_HEIGHT - 10);
            g2d.setPaint(Color.WHITE);

            turtle(g2d);
            g2d.dispose();
        }
    }

}