What are Transient and Volatile Modifiers

Question

Can someone explain what the transient and volatile modifiers mean in Java

User · Answer

Volatile means other threads can edit that particular variable. So the compiler allows access to them.

http://www.javamex.com/tutorials/synchronization_volatile.shtml

Transient means that when you serialize an object, it will return its default value on de-serialization

http://www.geekinterview.com/question_details/2

User · Answer

Transient     First need to know where it needed how it bridge the gap   1  An Access modifier transient is only applicable to variable component only   It will not used with method or class   2  Transient keyword cannot be used along with static keyword   3  What is serialization and where it is used  Serialization is the process of making the object s state persistent  That means the state of the object is converted into a stream of bytes to be used for persisting  e g  storing bytes in a file  or transferring  e g  sending bytes across a network   In the same way  we can use the deserialization to bring back the object s state from bytes  This is one of the important concepts in Java programming because serialization is mostly used in networking programming  The objects that need to be transmitted through the network have to be converted into bytes   Before understanding the transient keyword  one has to understand the concept of serialization  If the reader knows about serialization  please skip the first point   Note 1  Transient is mainly use for serialzation process   For that the class must implement the java io Serializable interface  All of the fields in the class must be serializable  If a field is not serializable  it must be marked transient   Note 2  When deserialized process taken place they get set to the default value - zero  false  or null as per type constraint   Note 3  Transient keyword and its purpose  A field which is declare with transient modifier it will not take part in serialized process  When an object is serialized saved in any state   the values of its transient fields are ignored in the serial representation  while the field other than transient fields will take part in serialization process  That is the main purpose of the transient keyword

User · Answer

The volatile and transient modifiers can be applied to fields of classes1 irrespective of field type   Apart from that  they are unrelated   The transient modifier tells the Java object serialization subsystem to exclude the field when serializing an instance of the class   When the object is then deserialized  the field will be initialized to the default value  i e  null for a reference type  and zero or false for a primitive type  Note that the JLS  see 8 3 1 3  does not say what transient means  but defers to the Java Object Serialization Specification  Other serialization mechanisms may pay attention to a field s transient-ness    Or they may ignore it     Note that the JLS permits a static field to be declared as transient   This combination doesn t make sense for Java Object Serialization  since it doesn t serialize statics anyway   However  it could make sense in other contexts  so there is some justification for not forbidding it outright    The volatile modifier tells the JVM that writes to the field should always be synchronously flushed to memory  and that reads of the field should always read from memory   This means that fields marked as volatile can be safely accessed and updated in a multi-thread application without using native or standard library-based synchronization   Similarly  reads and writes to volatile fields are atomic   This does not apply to   non-volatile lt  lt  long or double fields  which may be subject to  word tearing  on some JVMs    The relevant parts of the JLS are 8 3 1 4  17 4 and 17 7     1 - But not to local variables or parameters

User · Answer

volatile and transient keywords  1  transient keyword is used along with instance variables to exclude them from serialization process  If a field  is transient its value will not be persisted   On the other hand  volatile keyword is used to mark a Java variable as  being stored in main memory    Every read of a volatile variable will be read from the computer s main memory  and not from the CPU cache  and that every write to a volatile variable will be written to main memory  and not just to the CPU cache   2  transient keyword cannot be used along with static keyword but volatile can be used along with static   3  transient variables are initialized with default value during de-serialization and there assignment or restoration of value has to be handled by application code   For more information  see my blog  http   javaexplorer03 blogspot in 2015 07 difference-between-volatile-and html

[java] What are Transient and Volatile Modifiers?

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