||Instances of DatabaseError are passed to callbacks when an operation failed.
||A Firebase reference represents a particular location in your Database and can be used for
reading or writing data to that Database location.
||A DataSnapshot instance contains data from a Firebase Database location.
||The entry point for accessing a Firebase Database.
||Due to the way that Java implements generics (type-erasure), it is necessary to use a slightly
more complicated method to properly resolve types for generic collections at runtime.
||Instances of this class encapsulate the data and priority at a location.
||The OnDisconnect class is used to manage operations that will be run on the server when this
||The Query class (and its subclass,
DatabaseReference) are used for reading data.
||Contains placeholder values to use when writing data to the Firebase Database.
||The Transaction class encapsulates the functionality needed to perform a transaction on the data
at a location.
||Instances of this class represent the desired outcome of a single run of a