Android Custom Dialog without title

AlertDialog alertDialog;
AlertDialog.Builder builder = new AlertDialog.Builder(this);
LayoutInflater inflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
View layout = inflater.inflate(R.layout.linkpopup,null);
CheckBox dontdisplay=(CheckBox)layout.findViewById(R.id.dontdisplay);
Button popupok=(Button)layout.findViewById(R.id.linkpopupok);
dontdisplay.setOnCheckedChangeListener(new OnCheckedChangeListener(){
      @Override
      public void onCheckedChanged(CompoundButton buttonView,    boolean isChecked) {
             if(isChecked)
                        db.updateDegfaultvalues("dontflag",1);
            else
                        db.updateDegfaultvalues("dontflag",0);
       }
});
popupok.setOnClickListener(new OnClickListener(){
    @Override
     public void onClick(View arg0) {
             alertDialog.cancel();
    }
});
       builder.setView(layout);
       alertDialog = builder.create();
       alertDialog.show();