boundingbox.java

@Override
	public void addCollisionBoxesToList(World world, int x, int y, int z, AxisAlignedBB blockBounds, List list, Entity collidingEntity) {
	// you should use blockBounds as a "mask". Only the intersection of all BoundingBoxes and blockBounds should be added
	// (this basically means that you should offset your bounding box by the block's position)
	// The list is the list you should add your bounding boxes to by calling list.add(AxisAlignedBoundBox); 
	// Also by sure that you add different bounding box objects for every bounding box. The bounds are NOT copied when you add
	// it to the list so changes to the added box will be reflected in the list. Just instantiate a new AxisAlignedBoundingBox for
	// every box you add.
	// You may use collidingEntity to let different entities board (only players?)
		//this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 2.0F, 1.0F);
		int m = world.getBlockMetadata(x, y, z);
		System.out.println("meta = "+m);
		switch (m) {
			case 2: this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 2.0F, 0.2F); 
			case 3: this.setBlockBounds(0.0F, 0.0F, 0.8F, 1.0F, 2.0F, 1.0F);
			case 4: this.setBlockBounds(0.8F, 0.0F, 0.0F, 1.0F, 2.0F, 1.0F);
			case 5: this.setBlockBounds(0.0F, 0.0F, 0.0F, 0.2F, 2.0F, 1.0F);
		}
        super.addCollisionBoxesToList(world,x,y,z,blockBounds,list,collidingEntity);
	}