Hello Java 26

1.txt

// Java 25
$java -version
openjdk version "25" 2025-09-16
OpenJDK Runtime Environment (build 25+35-3488)
OpenJDK 64-Bit Server VM (build 25+35-3488, mixed mode, sharing)

$java Hello.java       
Hello
Goodbye


// Java 26
$java -version
openjdk version "26" 2026-03-17
OpenJDK Runtime Environment (build 26+35-2893)
OpenJDK 64-Bit Server VM (build 26+35-2893, mixed mode, sharing)

$java Hello.java       
Hello
WARNING: Final field finalField in class Demo1 has been mutated reflectively by class Hello in unnamed module @6c3f5566 (file:/Users/somkiatpuisungnoen/data/slide/java/learn/java26/Hello.java)
WARNING: Use --enable-final-field-mutation=ALL-UNNAMED to avoid a warning
WARNING: Mutating final fields will be blocked in a future release unless final field mutation is enabled
Goodbye

## Disable การแก้ไข
$java --illegal-final-field-mutation=deny Hello.java

DemoClient.java

var client = HttpClient.newBuilder()
       .version(HttpClient.Version.HTTP_3)
       .build();


var request = HttpRequest.newBuilder(URI.create("https://somkiat.cc"))
        .version(HttpClient.Version.HTTP_3)
        .GET().build();

DemoLazy.java

import java.util.logging.Logger;

class OrderController {
    // OLD:
    // private Logger logger = null;

    // NEW:
    private final LazyConstant<Logger> logger = LazyConstant
            .of(() -> Logger.getLogger(OrderController.class.getName()));

    public void submitOrder() {
        // Access the constant value using get()
        logger.get().info("Order started");
    }
}

public class DemoLazy {
    public static void main(String[] args) {
        OrderController controller = new OrderController();
        controller.submitOrder();
    }
}

Hello.java

class Demo1 {
    final String finalField;

    Demo1() {
        finalField = "Hello";
    }
}

public class Hello {
    void main() throws Exception {
        java.lang.reflect.Field f = Demo1.class.getDeclaredField("finalField");
        f.setAccessible(true);

        Demo1 obj = new Demo1();
        System.out.println(obj.finalField); // Prints "Hello"

        f.set(obj, "Goodbye");
        System.out.println(obj.finalField); // Prints "Goodbye"
    }
}