Java 16 – Sealed Classes to restrict implementation

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Java 16, the latest release of the Java programming language, introduces sealed classes, a powerful new feature that allows developers to restrict the set of classes that can extend or implement a particular class or interface. In this blog post, we’ll take a closer look at what sealed classes are and how they can benefit Java developers.

What are sealed classes?

Sealed classes are a way of modeling hierarchies of classes and interfaces in a more robust and secure way. With sealed classes, you can define a class or interface that can only be extended or implemented by a specific set of classes. This allows you to control which classes can be used as implementations of your interfaces or as subclasses of your base classes.

Sealed classes are declared using the ‘sealed’ keyword followed by the name of the class or interface. You can then specify the list of classes or interfaces that are allowed to extend or implement the sealed class or interface using the ‘permits’ keyword followed by the list of allowed classes or interfaces.

Here’s an example of how to define a sealed class:

public sealed class Shape permits Circle, Square, Triangle {
   // class definition

In this example, the Shape class is declared as sealed, and it permits three classes: Circle, Square, and Triangle. This means that only these three classes can extend the Shape class.

What are the benefits of sealed classes?

Sealed classes provide several benefits for Java developers:

  1. Enhanced security: By restricting the set of classes that can extend or implement a sealed class or interface, you can reduce the risk of security vulnerabilities caused by unauthorized or malicious code.
  2. Improved code maintainability: Sealed classes make it easier to maintain code over time by ensuring that the set of allowed subclasses or implementations is well-defined and controlled.
  3. Better code design: Sealed classes encourage better code design by forcing developers to think more carefully about the class hierarchy and the relationships between classes and interfaces.
  4. Better error handling: Sealed classes can improve error handling by ensuring that only well-defined classes or interfaces can be used as implementations or subclasses.

In conclusion, sealed classes are a powerful new feature introduced in Java 16 that provides enhanced security, improved code maintainability, better code design, and better error handling. By restricting the set of classes that can extend or implement a particular class or interface, sealed classes provide a more robust and secure way of modeling class hierarchies in Java.

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