By design, the ArrayList class in Java is serializable by default. This means you don't need to implement any special interfaces to write an ArrayList to a byte stream using ObjectOutputStream . The real catch is that every inside that list must also implement java.io.Serializable . If even one object in a list of thousands fails this requirement, the entire process crashes with a NotSerializableException . The "Disaster" of Java Serialization
It bypasses constructors and uses reflection to "scrape" private fields directly from memory to create a byte stream. Android Java Serialize Arraylist
While functional, standard Java serialization is often described by language designers as a "disaster" for several reasons: By design, the ArrayList class in Java is