JAVA EE: Static Keyword

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Tuesday, 4 October 2016

Java Tutorial : Java IO (Java Serialization with static data member)

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Introduction

A classic interview and core Java conceptual question is: What happens to a static data member during object serialization? In Java, serialization is designed to persist the state of an object instance. Because static members belong to the class definition rather than any single instance, their behavior during serialization follows distinct rules.

Why Static Variables Are Not Serialized

In Java, static variables are loaded into memory when the class itself is loaded and are shared across all instances of that class.

Instance State vs Class State: Serialization persists only an instance's non-static fields. Static fields represent class-level state and are completely skipped by ObjectOutputStream.
No Storage in Byte Stream: The byte stream created during serialization contains no record of the static variable's value at the time the object was serialized.

What Happens During Deserialization?

When the object is deserialized using ObjectInputStream, Java loads the class if it is not already loaded. The static field will reflect whatever value is currently loaded in the JVM's memory, not the value it held when the object was written to the stream.

If the static variable was modified after serialization took place, reading the object back will expose that updated static value—proving it was never persisted with the object.

Static vs Transient in Serialization

Feature	`static` Variable	`transient` Variable
Belongs To	Class level	Object instance level
Serialized?	No	No
Value After Deserialization	Current value in JVM memory	Default data type value (null, 0, false)