1. Sealed Classes

• Description: Sealed classes allow developers to restrict which classes can extend or implement a given class or interface. This provides a more controlled inheritance hierarchy.
• Use Case:
  • Define closed hierarchies for business logic, ensuring only specific subclasses are allowed.
  • Useful in modeling scenarios like a Payment hierarchy with subclasses such as CreditCardPayment, PaypalPayment, etc.
• Code Example:

public sealed class Payment permits CreditCardPayment, PaypalPayment {
   public abstract void process();
}

public final class CreditCardPayment extends Payment {
   @Override
   public void process() {
       // Implementation
   }
}

public final class PaypalPayment extends Payment {
   @Override
   public void process() {
       // Implementation
   }
}
 

2. Pattern Matching for Switch (Preview)

• Description: Enhanced switch statements now support pattern matching, simplifying type-checking and extraction logic.
• Use Case:
  • Handle various types of objects in a single, concise block.
  • Improve readability and maintainability of complex decision logic.
• Code Example:

public static String formatValue(Object value) {
   return switch (value) {
       case Integer i -> "Integer: " + i;
       case String s -> "String: " + s;
       case null -> "Null value";
       default -> "Unknown type";
   };
}

3. Text Blocks

• Description: Introduced in Java 15 and part of Java 17, text blocks simplify handling of multi-line strings.
• Use Case:
  • Write cleaner code for SQL queries, JSON, XML, or HTML templates.
  • Improve readability and reduce boilerplate code.
• Code Example:

String jsonTemplate = """
   {
       "name": "%s",
       "age": %d,
       "address": "%s"
   }
   """;
 

4. New macOS Rendering Pipeline (JEP 382)

• Description: The new rendering pipeline replaces Apple's deprecated OpenGL.
• Use Case:
  • Ensures compatibility and performance improvements for GUI applications on macOS.
• Complex Project Application:
  • Enterprise-grade GUI applications for data visualization.

5. Enhanced Random Number Generators (JEP 356)

• Description: New interfaces and classes for random number generation, such as RandomGenerator and support for stream-based programming.
• Use Case:
  • Cryptography, simulations, gaming, or data sampling.
• Code Example:

RandomGenerator generator = RandomGenerator.of("L128X256MixRandom");
generator.ints(5, 1, 100).forEach(System.out::println);
 

6. Removal of Deprecated Features

• Description:
  • Deprecated features like RMI Activation, Applet API, and others have been removed, ensuring a cleaner ecosystem.
• Use Case:
  • Encourages migration to modern alternatives like web technologies.

7. Foreign Function & Memory API (Preview)

• Description: Enables Java applications to interoperate with code and data outside the JVM safely.
• Use Case:
  • Integrate with C libraries for performance-critical applications like machine learning or multimedia processing.
• Code Example:

try (MemorySegment segment = MemorySegment.allocateNative(1024)) {
   MemoryAccess.setIntAtOffset(segment, 0, 42);
   int value = MemoryAccess.getIntAtOffset(segment, 0);
   System.out.println(value);
}
 

8. Deprecating Finalization (JEP 421)

• Description: Finalization is deprecated to prepare for its removal, encouraging use of alternative resource management techniques like try-with-resources.
• Use Case:
  • Avoid reliance on unpredictable garbage collection for resource cleanup.

9. Context-Specific Deserialization Filters

• Description: Simplifies configuration of deserialization filters for security.
• Use Case:
  • Protect against deserialization vulnerabilities in distributed systems.

Complex Project Implementation

Let’s consider a financial application leveraging Java 17 features:

Features Used:

• Sealed Classes for modeling transaction types.
• Pattern Matching for Switch for processing various event types.
• Text Blocks for generating SQL and JSON responses.
• RandomGenerator for generating secure IDs.
• Foreign Memory API for handling large datasets.

Sample Code:

public sealed interface Transaction permits Deposit, Withdrawal, Transfer {}

public final class Deposit implements Transaction {
   private final double amount;
   public Deposit(double amount) { this.amount = amount; }
}

public final class Withdrawal implements Transaction {
   private final double amount;
   public Withdrawal(double amount) { this.amount = amount; }
}

public final class Transfer implements Transaction {
   private final double amount;
   private final String account;
   public Transfer(double amount, String account) {
       this.amount = amount;
       this.account = account;
   }
}

public static void handleTransaction(Transaction tx) {
   switch (tx) {
       case Deposit d -> System.out.println("Processing deposit: " + d.amount);
       case Withdrawal w -> System.out.println("Processing withdrawal: " + w.amount);
       case Transfer t -> System.out.println("Transferring " + t.amount + " to " + t.account);
       default -> throw new IllegalArgumentException("Unknown transaction");
   }
}