Skip to main content

Notice: This Wiki is now read only and edits are no longer possible. Please see: https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/wikis/Wiki-shutdown-plan for the plan.

Jump to: navigation, search

Java19/Examples

This is an informal page listing examples of features that are implemented by the Java 19 Support, which can be installed from the Marketplace. You are welcome to try out these examples. If you find bugs, please file a bug after checking for a duplicate entry here

Watch out for additional examples being added soon.

NOTE:

  • Pattern Matching for switch is a preview feature in Java 19. They are not enabled by default and can by enabled using --enable-preview.
  • Record Patterns is a preview feature in Java 19. They are not enabled by default and can by enabled using --enable-preview.
  • Virtual Threads is a preview feature in Java 19. They are not enabled by default and can by enabled using --enable-preview.
  • Structured Concurrency is a incubator features in Java 19.
  • In Eclipse, --enable-preview can be enabled from the Preferences > Java > Compiler. It is implicitly added while launching a java program if the feature has been enabled for the project/workspace.
Feature / Steps Expected Result
Standard Java/JRE setup with Eclipse More details can be found on dedicated Java/JRE setup page. Setting up Java/JRE in Eclipse.
Overview of eclipse.ini More details can be found on dedicated eclipse.ini page. Specifying the JVM in eclipse.ini
Preview Feature: Pattern Matching for switch
Positive compilation1 (Pattern Matching for switch Example) Use the following code: 
package pkg1;
public class X {
	@SuppressWarnings("preview")
	private static void foo(Object o) {
	   switch (o) {
	     case Integer i     -> System.out.println("String:");
	     case String s     	-> System.out.println("String: Hello World!");
	     default       	-> System.out.println("Object");
	   }
	}
 
	public static void main(String[] args) {
		foo("Hello World");
	}
}



Pattern-matching-switch-positive1-Java19.png

Code compiles and prints below message:

String: Hello World!

Positive compilation2 (Pattern Matching for switch Example) Use the following code: 
package pkg1;
public class X {
	@SuppressWarnings("preview")
	private static void foo(Object o) {
	   switch (o) {
	     case Integer I: 
	       System.out.println("Integer"); 
	       System.out.println(I); 
	       break; 
	     case String s when s.length()>1: 
	       System.out.println("String s && s.length()>1"); 
	       System.out.println(s); 
	       break;
	     case String s: 
	       System.out.println("String"); 
	       System.out.println(s);
	       break; 
	     case X x:
	       System.out.println("X"); 
	       System.out.println(x);
	       break;
	     default : System.out.println("Object"); 
	   }
	}
	public static void main(String[] args) {
		foo("Hello World!");
		foo("H");
		foo(new Object());
	}
}



Pattern-matching-switch-positive2-Java19.png

Code compiles and prints below message:

String s && s.length()>1
Hello World!
String
H
Object

Positive compilation3 (Pattern Matching for switch Example) Use the following code: 
package pkg1;
public class X {
	public static void main(String[] args) {
		foo(Integer.valueOf(11));
		foo(Integer.valueOf(9));
	}
 
	@SuppressWarnings("preview")
	private static void foo(Object o) {
	   switch (o) {
	   case Integer i when i>10:
	     System.out.println("Greater than 10:" + o);
	     break;
	   case Integer j when j>0:
	     System.out.println("Greater than 0:" + o);
	     break;
	   default:
	     System.out.println("Object" + o);
	   }
	}
}



Pattern-matching-switch-positive3-Java19.png

Code compiles and prints below message:

Greater than 10:11
Greater than 0:9

Positive compilation4 (Pattern Matching for switch Example) Use the following code: 
package pkg1;
public class X {
	@SuppressWarnings("preview")
	public static void foo(Object o) throws Exception {
		switch (o) {
			case String s1:
				throw new Exception(s1);
			default:
				break;
		}
	}
 
	public static void main(String[] args) throws Exception {
		foo("hello");
	}
}



Pattern-matching-switch-positive4-Java19.png

Code compiles and prints below exception stack trace message:

Exception in thread "main" java.lang.Exception: hello
at BetaJava19/pkg1.X.foo(X.java:7)
at BetaJava19/pkg1.X.main(X.java:14)

Preview Feature: Record Patterns
Positive compilation1 (Record Patterns Example) Use the following code: 
package pkg1;
 
record Point(int x, int y) {}
record Length(int l) {}
 
public class A {
	@SuppressWarnings("preview")
	static void printObject(Object obj) {
		if (obj instanceof Point(int x, int y)) {
			System.out.println("Point.x= " + x + "\nPoint.y= " + y);
		} else if (obj instanceof Length(int l)) {
			System.out.println("Lenght.l= " + l);
		} else {
			System.out.println(obj);
		}
	}
 
	public static void main(String[] args) {
		printObject(new Point(10, 20));
		printObject(new Length(100));
	}
}



Positive case1 RecordPatters Java19.png

Code compiles and prints below message:

Point.x= 10
Point.y= 20
Lenght.l= 100

Preview Feature: Virtual Threads
Positive compilation1 (Virtual Threads Example) Use the following code: 
package pkg1;
public class B {
	static Thread currentThread;
	@SuppressWarnings("preview")
	public static void main(String[] args) {
		Runnable runnable = () -> {
			System.out.println("---Start-Run---");
			if (currentThread.isVirtual()) {
				System.out.println("Virtual Thread:\n\tJava19 feature running with VM arguments:\n\t--enable-preview");
			} else {
				System.out.println("Standard Platform Thread:");
			}
			System.out.println("isVirtual: " + currentThread.isDaemon() + "\nisDaemon : " + currentThread.isDaemon());
			System.out.println("---End---Run---");
		};
		currentThread = new Thread(runnable); // Normal thread is non-daemon by default
		currentThread.start();
		currentThread = Thread.startVirtualThread(runnable); // Virtual thread is by default daemon
		try {
			Thread.sleep(100); // Sleep for 100 ms
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}



Positive Test case1 Virtual thread.png

Code compiles and prints below message:

---Start-Run---
Standard Platform Thread:
isVirtual: false
isDaemon : false
---End---Run---
---Start-Run---
Virtual Thread:
Java19 feature running with VM arguments:
--enable-preview
isVirtual: true
isDaemon : true
---End---Run---

Positive compilation2 (Virtual Threads Example) Use the following code: 
package pkg1;
public class C {
	static Thread currentThread;
	@SuppressWarnings("preview")
	public static void main(String[] args) {
		Runnable runnable = () -> {
			System.out.println("---Start-Run---");
			if (currentThread.isVirtual()) {
				System.out.println("Virtual Thread:\n\tJava19 feature running with VM arguments:\n\t--enable-preview");
			} else {
				System.out.println("Standard Platform Thread:");
			}
			System.out.println("isVirtual: " + currentThread.isDaemon() + "\nisDaemon : " + currentThread.isDaemon());
			System.out.println("---End---Run---");
		};
		currentThread = new Thread(runnable); // Normal thread is non-daemon by default
		currentThread.start();
		Thread.Builder threadBuilder = Thread.ofVirtual().name("Virtual-Thread", 1);
		currentThread = threadBuilder.start(runnable); // Virtual thread is by default daemon
		try {
			Thread.sleep(100); // Sleep for 100 ms
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}



Positive Test case2 Virtual thread.png

Code compiles and prints below message:

---Start-Run---
Standard Platform Thread:
isVirtual: false
isDaemon : false
---End---Run---
---Start-Run---
Virtual Thread:
Java19 feature running with VM arguments:
--enable-preview
isVirtual: true
isDaemon : true
---End---Run---

Positive compilation3 (Virtual Threads Example) Use the following code: 
package pkg1;
 
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class D {
	static ExecutorService service;
 
	@SuppressWarnings("preview")
	public static void main(String[] args) {
		Runnable runnable = () -> {
			System.out.println("---Start-Run---");
			System.out.println(
					"VirtualThreadPerTaskExecutor:\n\tJava19 feature running with VM arguments:\n\t--enable-preview");
			System.out.println("---End---Run---");
		};
		service = Executors.newVirtualThreadPerTaskExecutor();
		service.execute(runnable);
		try {
			Thread.sleep(100); // Sleep for 100 ms
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}



Positive Test case3 Virtual thread.png

Code compiles and prints below message:

---Start-Run---
VirtualThreadPerTaskExecutor:
Java19 feature running with VM arguments:
--enable-preview
---End---Run---

Retrieved from "https://wiki.eclipse.org/index.php?title=Java19/Examples&oldid=446110"

This page was last modified 03:14, 22 October 2022 by Eclipsepedia anonymous user Unnamed Poltroon.

Back to the top