global boolean value is setting inside addListenerForSingleEventValue function, but not recognized in following if statement

I'm cycling through some children in firebase to see if the value of a key exists, and in my addListenerForSingleValueEvent function the key is found and a global boolean is set to true. However, after the function, the variable is set as false so the program does not enter the second if statement.

referenceClasses.addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                            if (snapshot.getKey().compareTo(combinedString) == 0) {
                                found = true;
                                break;
                            }
                        }
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) { }
                });

                if(found) {
                   //...
                }

I know found is set to true within the addListenerForSingleValueEvent through various inputs to my database. the boolean is instantiated as

boolean found;

globally, before any other functions. I even tried to implement two functions, one which sets the boolean and another which returns it but I ended up with the same results of the boolean being true within addListenerForSingleValueEvent and false in the if statement. Any ideas?