This is a scope issue. You have your queue named: "kassas", but you also have a variable in the parameters of your constructor named: "kassas", which is an int. When you don't use a qualifying keyword (such as this.), java will look for the variable with the closes scope. In this case, it is attempting to call the .length method on your kassas int parameter, not your kassas queue.
One solution is to use this.kassas.length (like you do when you construct the queue a few lines before), but a potentially "better" solution would be to rename the int kassas parameter to something which makes more sense (perhaps kassasLength).