Error SmartWall airpush, void is an invalid type for the variable onAdCached

Question

i have this code:

info.setOnClickListener(new OnClickListener(){
        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            if(ma==null)
                ma = new MA(my, adCallbackListener, true);   // ad caching is enabled

            ma.callAppWall();   //this will start the AppWall ad but it will not show you AppWall instantly.  
            @Override
            public void onAdCached(AdType adType) {


                //you will receive the information here if an ad is cached. 

            }

            ma.showCachedAd(my, AdType.appwall);


}});

The method onAdCached gives me the following error:

"void is an invalid type for the variable onAdCached" Why? I hope to resolve.