This program shows how to draw anti-aliased lines. It draws two diagonal lines to form an X; when 'r' is typed in the window, the lines are rotated in opposite directions. The example is ported from C examples in the OpenGL Programming Guide (known as the "red book").

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 package glredbook11;

import java.awt.event.*;
import javax.swing.JFrame;
import javax.media.opengl.*;
import javax.media.opengl.glu.*;

public class aargb
  extends JFrame
    implements GLEventListener, KeyListener
{
  private GLCapabilities caps;
  private GLCanvas canvas;
  private float rotAngle = 0f;
  private boolean rotate = false;

  public aargb()
  {
    super("aargb");

    caps = new GLCapabilities();
    canvas = new GLCanvas(caps);
    canvas.addGLEventListener(this);
    canvas.addKeyListener(this);
  
    getContentPane().add(canvas);
  }

  public void run()
  {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(512, 512);
    setLocationRelativeTo(null);
    setVisible(true);
    canvas.requestFocusInWindow();
  }

  public static void main(String[] args)
  {
    new aargb().run();
  }

  public void init(GLAutoDrawable drawable)
  {
    GL gl = drawable.getGL();
    //
    float values[] = new float[2];
    gl.glGetFloatv(GL.GL_LINE_WIDTH_GRANULARITY, values, 0);
    System.out.println("GL.GL_LINE_WIDTH_GRANULARITY value is " + values[0]);
    gl.glGetFloatv(GL.GL_LINE_WIDTH_RANGE, values, 0);
    System.out.println("GL.GL_LINE_WIDTH_RANGE values are " + values[0] + ", "
                       + values[1]);
    gl.glEnable(GL.GL_LINE_SMOOTH);
    gl.glEnable(GL.GL_BLEND);
    gl.glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA);
    gl.glHint(GL.GL_LINE_SMOOTH_HINT, GL.GL_DONT_CARE);
    gl.glLineWidth(1.5f);
    gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
  }

  public void display(GLAutoDrawable drawable)
  {
    GL gl = drawable.getGL();
    //
    gl.glClear(GL.GL_COLOR_BUFFER_BIT);
    gl.glColor3f(0.0f, 1.0f, 0.0f);
    gl.glPushMatrix();
    gl.glRotatef(-rotAngle, 0.0f, 0.0f, 0.1f);
    gl.glBegin(GL.GL_LINES);
    gl.glVertex2f(-0.5f, 0.5f);
    gl.glVertex2f(0.5f, -0.5f);
    gl.glEnd();
    gl.glPopMatrix();
    gl.glColor3f(0.0f, 0.0f, 1.0f);
    gl.glPushMatrix();
    gl.glRotatef(rotAngle, 0.0f, 0.0f, 0.1f);
    gl.glBegin(GL.GL_LINES);
    gl.glVertex2f(0.5f, 0.5f);
    gl.glVertex2f(-0.5f, -0.5f);
    gl.glEnd();
    gl.glPopMatrix();
    gl.glFlush();
    if (rotate) rotAngle += 1f;
    if (rotAngle >= 360f) rotAngle = 0f;
  }

  public void reshape(GLAutoDrawable drawable, int x, int y, int w, int h)
  {
    GL gl = drawable.getGL();
    GLU glu = new GLU();
    gl.glViewport(0, 0, w, h);
    gl.glMatrixMode(GL.GL_PROJECTION);
    gl.glLoadIdentity();
    if (w <= h) //
    glu.gluOrtho2D(-1.0, 1.0, -1.0 * (float) h / (float) w, //
        1.0 * (float) h / (float) w);
    else glu.gluOrtho2D(-1.0 * (float) w / (float) h, //
        1.0 * (float) w / (float) h, -1.0, 1.0);
    gl.glMatrixMode(GL.GL_MODELVIEW);
    gl.glLoadIdentity();
  }

  public void displayChanged(GLAutoDrawable drawable, boolean modeChanged,
      boolean deviceChanged)
  {
  }

  public void keyTyped(KeyEvent key)
  {
  }

  public void keyPressed(KeyEvent key)
  {
    switch (key.getKeyCode()) {
      case KeyEvent.VK_ESCAPE: 
        System.exit(0);
      case KeyEvent.VK_R:
        rotate = !rotate;
        canvas.display();
      default:
        break;
    }
  }

  public void keyReleased(KeyEvent key)
  {
  }
}

Source: Kiet Le's The Red Book Examples using JOGL