Solved Noobish question... spawning blocks

I'm just not understanding why this isn't working the way I think it should:

Code (Text):

    private void replaceBlock() {
        Bukkit.broadcastMessage("changed " + block.getType().name() + " to " + material.name());
        block.setType(material);
    }

In game, if I break a diamond ore, it should replace that block to cobblestone.
The debug message prints out:
"changed DIAMOND_ORE to COBBLESTONE"
but when I then call Block#setType it doesnt seem to update the block to cobblestone? ;/
also no errors in console... idk what Im doing wrong, never had to spawn blocks using code before

 

realised I had to cancel my event of breaking blocks, because apparantly the block break still goes through if you change the block type... anyway solved ;p