Java 17: What's New and What You Need to Know

Table of Contents

1. New Features in Java 17
2. Usage Methods
3. Common Practices
4. Best Practices
5. Conclusion
6. References

New Features in Java 17

Sealed Classes

Sealed classes and interfaces restrict which other classes or interfaces may extend or implement them. This is useful for creating a closed hierarchy.

// Define a sealed class
sealed class Shape permits Circle, Rectangle {
    // Common methods for shapes
}

// Sub - class of Shape
final class Circle extends Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    public double getRadius() {
        return radius;
    }
}

// Another sub - class of Shape
final class Rectangle extends Shape {
    private double length;
    private double width;

    public Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }

    public double getLength() {
        return length;
    }

    public double getWidth() {
        return width;
    }
}

Pattern Matching for instanceof

Pattern matching for instanceof allows you to simplify the code when checking and casting objects.

Object obj = "Hello";
if (obj instanceof String str) {
    System.out.println(str.toUpperCase());
}

Deprecation of Applet API

The Applet API has been deprecated since Java 9, and in Java 17, it is finally removed. Applets were used to embed small Java applications in web pages, but with the rise of modern web technologies, they have become obsolete.

Strongly Encapsulated JDK Internals

Java 17 further enhances the encapsulation of JDK internals, making it more difficult for code to access non - public internal APIs. This helps in writing more secure and maintainable code.

Usage Methods

Compiling and Running Java 17 Code

To compile and run Java 17 code, you first need to have the Java 17 JDK installed.

Compiling:

javac -source 17 -target 17 YourJavaFile.java

Running:

java YourJavaFile

Using Sealed Classes

When using sealed classes, you need to ensure that all permitted sub - classes are defined correctly. You can use them in a switch statement for pattern matching.

Shape shape = new Circle(5);
switch (shape) {
    case Circle circle -> System.out.println("Circle area: " + Math.PI * circle.getRadius() * circle.getRadius());
    case Rectangle rectangle -> System.out.println("Rectangle area: " + rectangle.getLength() * rectangle.getWidth());
}

Using Pattern Matching for instanceof

Pattern matching for instanceof can be used in conditional statements to reduce boilerplate code. You can also use it in methods to handle different types of objects in a more concise way.

public static void printInfo(Object obj) {
    if (obj instanceof Integer num) {
        System.out.println("Integer value: " + num);
    } else if (obj instanceof String str) {
        System.out.println("String value: " + str);
    }
}

Common Practices

Use Sealed Classes for Closed Hierarchies

When you have a well - defined set of sub - classes for a particular class or interface, use sealed classes. For example, in a game development scenario, if you have a Character class with different types like Warrior, Mage, and Archer, you can use a sealed class to restrict the types of characters.

sealed class Character permits Warrior, Mage, Archer {
    // Common character methods
}

final class Warrior extends Character {
    // Warrior - specific methods
}

final class Mage extends Character {
    // Mage - specific methods
}

final class Archer extends Character {
    // Archer - specific methods
}

Leverage Pattern Matching for instanceof

In code where you need to check the type of an object and perform different actions based on its type, use pattern matching for instanceof. This makes the code more readable and less error - prone.

Avoid Using Deprecated APIs

Since Java 17 has removed some deprecated APIs, make sure your codebase does not rely on them. If you are migrating an older project to Java 17, carefully review the code for any usage of deprecated APIs and replace them with modern alternatives.

Best Practices

Keep Your Codebase Up - to - Date

Regularly update your Java version to the latest LTS version like Java 17. This ensures that you can take advantage of the latest features, security patches, and performance improvements.

Follow Encapsulation Principles

With the enhanced encapsulation of JDK internals in Java 17, follow good encapsulation practices in your own code. Keep your classes and methods as private as possible, and only expose the necessary interfaces.

Write Unit Tests

When using new features like sealed classes and pattern matching for instanceof, write comprehensive unit tests to ensure that your code behaves as expected. This helps in catching any potential bugs early in the development cycle.

Conclusion

Java 17 brings a set of powerful new features that enhance the language’s expressiveness, security, and maintainability. Sealed classes and pattern matching for instanceof simplify the code and make it more readable. The removal of deprecated APIs and the enhanced encapsulation of JDK internals contribute to a more secure and future - proof codebase. By understanding the new features, usage methods, common practices, and best practices, developers can efficiently use Java 17 in their projects.

References

• Java 17 Release Notes
• The Java Tutorials - Oracle

In summary, Java 17 is a significant step forward in the evolution of the Java programming language, and developers should embrace these new features to write better code.