// only time you have to care explicitely for memomry managment.
FixtureDef fixtureDef = new FixtureDef();
fixtureDef.shape = groundPoly;
fixtureDef.filter.groupIndex = 0;
groundBody.createFixture(fixtureDef);
groundPoly.dispose();
PolygonShape boxPoly = new PolygonShape();
boxPoly.setAsBox(1, 1);
// Next we create the 50 box bodies using the PolygonShape we just