Problems with JOGL depth testing

Newbie & Debugging Questions
#1

I have been programming a jogl application and I can’t get deph testing to work. Can anyone with more experience than me sugfgest something i am missing, or something silly i have done?

I use the following code (in my class that implements GLEventListener) to enable depth testing,

	public void display(GLDrawable drawable) 
	{
		GL gl = drawable.getGL();
		GLU glu = drawable.getGLU();


		camera.position(gl, glu);

		//enable removal of hidden faces
		gl.glClear(GL.GL_DEPTH_BUFFER_BIT);
		gl.glEnable(GL.GL_DEPTH_TEST);
		gl.glDepthFunc(GL.GL_LEQUAL);

		gl.glClear(GL.GL_COLOR_BUFFER_BIT);

		owner.display(drawable);

		gl.glFlush();
	}

where owner.display(drawable) calls a display object function in all the objects in the universe, each of which either draws a quad of a triangle, as follows:

	public void displayObject(GLDrawable drawable)
	{
		GL gl = drawable.getGL();

		if(fill) { gl.glPolygonMode( GL.GL_FRONT, GL.GL_FILL ); gl.glPolygonMode( GL.GL_BACK,  GL.GL_POINT); }
		else { gl.glPolygonMode( GL.GL_FRONT_AND_BACK, GL.GL_LINE ); }

		//gl.glCullFace(GL.GL_FRONT_AND_BACK);
		//l.glPolygonMode( GL.GL_FRONT_AND_BACK, GL.GL_FILL );


		gl.glColor4f(colour[0], colour[1], colour[2], colour[3]);

		gl.glBegin(GL.GL_POLYGON);

		for(int i = 0; i < points.length; i++)
		{
			gl.glNormal3d(vertexNormals[i].getX(), vertexNormals[i].getY(), vertexNormals[i].getZ()); //Set the normal for the node
			gl.glVertex3d(points[i].getX(), points[i].getY(), points[i].getZ()); 
		}
		gl.glEnd();
	}