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Hazelcast needs to serialize the Java objects that you put into Hazelcast because Hazelcast is a distributed system. The data and its replicas are stored in different partitions on multiple cluster members. The data you need may not be present on the local member, and in that case, Hazelcast retrieves that data from another member. This requires serialization.

Serialization is used in the following cases:

  • Adding key/value objects to a map

  • Putting items in a queue/set/list

  • Sending a runnable using an executor service

  • Processing an entry within a map

  • Locking an object

  • Sending a message to a topic

Hazelcast optimizes the serialization for the basic types and their array types. You cannot override this behavior.

The following are the default types:

  • Byte, Boolean, Character, Short, Integer, Long, Float, Double, String

  • byte[], boolean[], char[], short[], int[], long[], float[], double[], String[]

  • java.util.Date, java.math.BigInteger, java.math.BigDecimal, java.lang.Class

Hazelcast optimizes all of the above object types. You do not need to worry about their (de)serializations.