Android upload data to Firebase realtime database

MainActivity.java

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_donations_details_entry);

  edtQuantity = (EditText)findViewById(R.id.edt_quantity);
  edtAddress = (EditText)findViewById(R.id.edt_address);
  edtFood = (EditText)findViewById(R.id.edt_food);
  edtPhone = (EditText)findViewById(R.id.edt_phone);

  findViewById(R.id.btn_donate).setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  submitDonation();
              }
  });
}

private void submitDonation() {
  quantity = Integer.parseInt(edtQuantity.getText().toString().trim());
  address = edtAddress.getText().toString().trim();
  foodName = edtFood.getText().toString().trim();
  phoneNumber = edtPhone.getText().toString().trim();

  String instanceName = getRandomString();
  FirebaseDatabase database = FirebaseDatabase.getInstance(); //follow Firebase setup in Android Studio (Tools > Firebase)
  DatabaseReference myQuant = database.getReference(instanceName+"/");
  myQuant.child("quantity").setValue(quantity);
  myQuant.child("address").setValue(address);
  myQuant.child("foodName").setValue(foodName);
  myQuant.child("phoneNumber").setValue(phoneNumber);
}

private String getRandomString(){
  Random generator = new Random();
  StringBuilder randomStringBuilder = new StringBuilder();
  int randomLength = generator.nextInt(20);
  char tempChar;
  for (int i = 0; i < randomLength; i++){
    tempChar = (char) (generator.nextInt(26) + 65);
    randomStringBuilder.append(tempChar);
  }
  return randomStringBuilder.toString();
}