Supported Java Features

Feature Supported Note

Classes
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Classes without default constructor
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Abstract classes / Interfaces
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Perfectly handleable as types, but there can never be instances to be persisted in the first place.

Inner classes
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Anonymous inner classes
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Primitives
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References
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Final fields
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Static fields
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Not supported since they are outside of an entity graph / a database, i.e. potentially shared by multiple graphs.

Constant primitives
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No sense in persisting those. These are just plain trivial values outside of an entity graph / a database.

Constant instances
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Must be registered for loading to update them instead of creating independent new instances.

Primitive arrays
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Object arrays
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Multi dimensional arrays
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Technically the same as object arrays as every array is an object itself.

JDK value types (String, Number types, Date, File, Locale, Optional, …​)
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Optimized handling via custom TypeHandlers.

Collections
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Via generic handling logic (List, Set, Map, etc.). Optimal handling required tailored TypeHandler (e.g. correctly handling loadFactor in java.util.HashMap)

Nested Collections
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JVM system-tied classes (Thread, ClassLoader, WeakReference, …​)
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Technically handleable, but handling system-instances could cause fatal problems (e.g. start a Thread just from loading data), so it is intentionally disabled.

JVM external-tied classes (IO-Streams, FileChannel, …​)
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Technically handleable, but external dependencies could cause fatal problems (e.g. existence of a referenced file), so it is intentionally disabled.

Java 5

Feature Supported Note

Enums
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Automatically handled as constant instances to maintain referential integrity / identity.

Enums with mutable state
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Enums anonymous subclasses
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Java 8

Feature Supported Note

Lambdas
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Type-handleable in theory. But JVM is not able to resolve its own type definitions for lambdas.

Java 14

Feature Supported Note

Records
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Records are mere syntax sugar for classes, see FAQ.