A NEWT JogAmp JOGL 2 port of: https://sites.google.com/site/justinscsstuff/jogl-tutorial-3

SimpleScene.java

/*
# This code is a NEWT JogAmp JOGL 2 port of:
# https://sites.google.com/site/justinscsstuff/jogl-tutorial-3
#
# Get the latest JogAmp JOGL 2
wget http://jogamp.org/deployment/jogamp-current/archive/jogamp-all-platforms.7z
7z x jogamp-all-platforms.7z
cd jogamp-all-platforms

# Compile this demo.
javac -cp jar/jogl-all.jar:jar/gluegen-rt.jar SimpleScene.java

# And run it!
java -cp jar/jogl-all.jar:jar/gluegen-rt.jar:. SimpleScene

# Xerxes Rånby
*/

import javax.media.opengl.*;
import com.jogamp.opengl.util.*;
import com.jogamp.newt.opengl.GLWindow;

public class SimpleScene implements GLEventListener {

    private double theta = 0;
    private double s = 0;
    private double c = 0;

    public static void main(String[] args) {
        GLProfile glp = GLProfile.getDefault();
        GLCapabilities caps = new GLCapabilities(glp);
        GLWindow window = GLWindow.create(caps);

        window.setSize(300, 300);
        window.setVisible(true);

        window.addGLEventListener(new SimpleScene());

        FPSAnimator animator = new FPSAnimator(window, 60);
        animator.add(window);
        animator.start();
    }

    @Override
    public void display(GLAutoDrawable drawable) {
        update();
        render(drawable);
    }

    @Override
    public void dispose(GLAutoDrawable drawable) {
        System.exit(0);
    }

    @Override
    public void init(GLAutoDrawable drawable) {
    }

    @Override
    public void reshape(GLAutoDrawable drawable, int x, int y, int w, int h) {
    }

    private void update() {
        theta += 0.01;
        s = Math.sin(theta);
        c = Math.cos(theta);
    }

    private void render(GLAutoDrawable drawable) {
        GL2 gl = drawable.getGL().getGL2();

        gl.glClear(GL.GL_COLOR_BUFFER_BIT);

        // draw a triangle filling the window
        gl.glBegin(GL.GL_TRIANGLES);
        gl.glColor3f(1, 0, 0);
        gl.glVertex2d(-c, -c);
        gl.glColor3f(0, 1, 0);
        gl.glVertex2d(0, c);
        gl.glColor3f(0, 0, 1);
        gl.glVertex2d(s, -s);
        gl.glEnd();
    }
}

Same issue as BonzaiThePenguin (his fix works):

Drawable already added to animator