Class SealedClassesPreviewExamples

java.lang.Object

net.jrodolfo.java_evolution.java15.SealedClassesPreviewExamples

public class SealedClassesPreviewExamples
extends Object

Demonstrates sealed classes as a Java 15 preview feature.

Before sealed classes, a type hierarchy was usually open to any subtype that could access the parent type. That made it difficult to model small closed domains directly in the type system.

Sealed classes solve this by letting the parent type explicitly list permitted subtypes. They became final in Java 17. The sealed-type syntax shown here is also faithful to the Java 15 preview, while the documentation identifies its preview status.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final record	SealedClassesPreviewExamples.Circle	Circle implementation permitted by SealedClassesPreviewExamples.Shape.
static final record	SealedClassesPreviewExamples.Rectangle	Rectangle implementation permitted by SealedClassesPreviewExamples.Shape.
static interface	SealedClassesPreviewExamples.Shape	Sealed parent type that explicitly lists permitted implementations with permits.

Constructor Summary

Constructors

Constructor	Description
SealedClassesPreviewExamples()

Method Summary

Modifier and Type	Method	Description
double	area(SealedClassesPreviewExamples.Shape shape)	Calculates the area of a known shape hierarchy.
String	java15ReflectionApiSource()	Returns the reflection API shape from the Java 15 first preview.
List<String>	permittedShapeNames()	Lists the classes explicitly permitted by the sealed SealedClassesPreviewExamples.Shape parent.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

SealedClassesPreviewExamples

public SealedClassesPreviewExamples()

Method Details

area

public double area(SealedClassesPreviewExamples.Shape shape)

Calculates the area of a known shape hierarchy.

Parameters:

shape - the shape to measure

Returns:

the shape area

permittedShapeNames

public List<String> permittedShapeNames()

Lists the classes explicitly permitted by the sealed SealedClassesPreviewExamples.Shape parent.

Returns:

permitted subtype simple names

java15ReflectionApiSource

public String java15ReflectionApiSource()

Returns the reflection API shape from the Java 15 first preview.

The preview method is preserved as source text because the current JDK exposes the later getPermittedSubclasses() API instead.

Returns:

Java 15 preview reflection source