Sealed type
A sealed type is a class or interface that restricts which other types may directly extend or implement it to a permitted set.
100 Java Mistakes and How to Avoid Them
A sealed interface is a Java interface that restricts which classes or interfaces may directly implement or extend it.
- How it is used
- Uses a closed Entry hierarchy to make list processing exhaustive at compile time.
- How deep it goes
- Defines a sealed interface hierarchy and demonstrates compiler-checked exhaustive switching, without detailing broader hierarchy design.
- Examples
- Uses Entry with IntEntry and StringEntry records to process a list through an exhaustive switch.
- What you can do after
- Apply via the Java 21 compiler to force handling of newly added inheritors.
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Kotlin in Action, 2E
A sealed interface is a Kotlin interface whose implementations are restricted to a known set once its containing module is compiled.
- How it is used
- Restricts interface implementations so closed hierarchies can be handled exhaustively with when expressions.
- How deep it goes
- Explains module-level implementation restrictions and compiler exhaustiveness, stopping short of broader hierarchy mechanics.
- Examples
- Uses Toggleable with LightSwitch and Camera, alongside expression hierarchies demonstrating exhaustive evaluation.
- What you can do after
- Build it from scratch by declaring a sealed interface, implementing it, and relying on compiler-checked exhaustive when handling.
Related concepts
- natural language interfacekind of · A natural language interface enables interaction with a system through human-language text or speech.
- union typeimplements · A union type is a type whose values can be any one of several specified alternative types or variants.
- compileruses · A compiler is software that translates source code into executable code or another representation, while analyzing it according to the source language’s rules.
- HTTP response codeproduces · An HTTP status code is a standardized three-digit value in an HTTP response that indicates the outcome of processing the corresponding request.
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