Sealed Classes in Java 17
An Introduction
What are Sealed Classes?
Sealed classes are a feature introduced in Java 16 (as a preview feature) and finalized in Java 17.
Sealed classes allow developers to restrict the inheritance hierarchy of a class or interface. In other words, they provide more control over how a class can be extended or implemented.
Code Example for a Sealed class
Take a Shapeclass, which can be extended by Circle, Square, or Triangle classes. With Sealed Classes, we can specify that only these three classes can inherit from Shape, and no other class can extend it.
Check syntax below:
public sealed class Shape permits Circle, Square, Triangle {
// Class definition
}Above, we have defined a sealed class, Shape, which allows only Circle, Square, and Triangle to extend it.
1. Defining a sealed class
public sealed interface Vehicle permits Car, Bike {
void start();
}In this example, we have defined a sealed interface calledVehiclewhich permits only Car and Bike classes to implement it. The interface defines a single method called start().
