Sealed Classes (JEP 409): Java 17 introduces sealed classes, a new language feature that allows developers to restrict the set of classes that can extend or implement a particular class or interface. Sealed classes offer improved control over class hierarchies, making code more maintainable and secure. By explicitly specifying which classes can extend a sealed class, developers can prevent unauthorized subclassing, reducing the risk of unintended behavior and vulnerabilities.
To declare a sealed class, use the "sealed" modifier followed by the permitted subclasses. Subclasses can be declared using the "non-sealed" modifier for classes with unrestricted subclassing or the "sealed" modifier for further constraining subclassing.
public sealed class Shape permits Circle, Rectangle, Triangle {
// Class definition
}
public final class Circle extends Shape {
// Class definition
}
public non-sealed class Rectangle extends Shape {
// Class definition
}
public non-sealed class Triangle extends Shape {
// Class definition
}
Pattern Matching for Switch (JEP 406): Pattern matching for switch expressions is another noteworthy addition in Java 17. This feature enhances the expressiveness and readability of switch statements by allowing developers to combine pattern matching with switch expressions. With pattern matching, switch expressions can now destructure and extract components from objects, facilitating concise and intuitive code. Visit - Java Course in Ahmednagar
Consider the following example where we use pattern matching to handle different shapes:
public double calculate area(Shape shape) {
return switch (shape) {
case Circle c -> Math.PI * c.getRadius() * c.getRadius();
case Rectangle r -> r.getLength() * r.getWidth();
case Triangle t -> 0.5 * t.getBase() * t.getHeight();
default -> throw new IllegalArgumentException("Unknown shape: " + shape);
};
}
Pattern matching simplifies code by eliminating the need for explicit type casting and instance checks, resulting in cleaner and more maintainable code.
Foreign Function and Memory API (JEP 412): Java 17 introduces the Foreign Function and Memory API, providing a standardized, safe, and efficient mechanism for interacting with native code and memory outside the Java Virtual Machine (JVM). This feature enables seamless integration with native libraries and systems programming languages like C and C++, opening up new possibilities for developers to leverage existing native code and libraries within their Java applications.
The Foreign Function and Memory API consists of several interfaces and classes for representing native memory segments, managing memory access, and defining native function signatures. By using these APIs, developers can interact with native code without sacrificing type safety or performance.
Here's a basic example demonstrating the usage of the Foreign Function and Memory API to call a native function:
import jdk.incubator.foreign.*;
public class Example {
public static void main(String[] args) {
try (var scope = MemoryScope.stack()) {
MemorySegment buffer = scope.allocateNative(1024); // Allocate native memory
CLinker.getInstance().downcallVoid("someNativeFunction", "(N)V", buffer.address()); // Call native function
}
}
}
Strongly Encapsulate JDK Internals by Default (JEP 396): Java 17 strengthens encapsulation by default, further enhancing the modularity and security of the Java platform. With this change, internal APIs within the Java Development Kit (JDK) are strongly encapsulated by default, making them inaccessible to external code unless explicitly opened via modules.
Strong encapsulation prevents unintended access to internal JDK APIs, reducing the risk of compatibility issues and security vulnerabilities caused by unauthorized usage. Developers can still access internal APIs for testing and debugging purposes by adding the "--add-exports" command-line option to open specific packages to external modules. Visit - Java Training in Ahmednagar
