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Java19/Examples

Revision as of 02:27, 19 September 2022 by Niraj.modi.in.ibm.com (Talk | contribs)

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. 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
Postive compilation1 (Pattern Matching for switch Example) Use the following code: 
public class X {
	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-Java17.png

Code compiles and prints below message:

String: Hello World!

Positive compilation2 (Pattern Matching for switch Example) Use the following code: 
public class X {
	private static void foo(Object o) {
	   switch (o) {
	     case Integer I: System.out.println("Integer"); break;
	     case String s && s.length()>1: System.out.println("String > 1"); break;
	     case String s1: System.out.println("String"); break;
	     case X x: System.out.println("X"); break;
	     default : System.out.println("Object");
	   }
	}
 
	public static void main(String[] args) {
		foo("Hello World!");
		foo("H");
		foo(bar());
	}
 
	public static Object bar() {
		return new Object();
	}
}



Pattern-matching-switch-positive2-Java17.png

Code compiles and prints below message:

String > 1
String
Object

Positive compilation3 (Pattern Matching for switch Example) Use the following code: 
public class X {
	private static void foo(Object o) {
	   switch (o) {
	     case Integer I: 
	       System.out.println("Integer"); 
	       System.out.println(I); 
	       break; 
	     case String s && 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(bar());
	}
 
	public static Object bar() {
		return new Object();
	}
}



Pattern-matching-switch-positive3-Java17.png

Code compiles and prints below message:

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

Positive compilation4 (Pattern Matching for switch Example) Use the following code: 
public class X {
	public static void main(String[] args) {
		foo(Integer.valueOf(11));
		foo(Integer.valueOf(9));
	}
 
	private static void foo(Object o) {
	   switch (o) {
	   case Integer i && i>10:
	     System.out.println("Greater than 10:" + o);
	     break;
	   case Integer j && j>0:
	     System.out.println("Greater than 0:" + o);
	     break;
	   default:
	     System.out.println("Object" + o);
	   }
	}
}



Pattern-matching-switch-positive4-Java17.png

Code compiles and prints below message:

Greater than 10:11 Greater than 0:9

Positive compilation5 (Pattern Matching for switch Example) Use the following code: 
public class X {
	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-positive5-Java17.png

Code compiles and prints below exception stack trace message:

Exception in thread "main" java.lang.Exception: hello
at X.foo(X.java:5)
at X.main(X.java:12)

Preview Feature: Record Patterns
Positive compilation1 (Code Snippets in Java API documentation Example) Use the following code: 
package pkg1;
 
/**
 * An example of internal Java-doc Snippet
 * {@snippet :
 *    System.out.println("Hello World"); // @highlight substring="System" type="highlighted"
 *    System.out.println("Hello World"); // @replace region="one" substring="Hello World" replacement="Hello All"
 *    System.out.println("Hello World"); // @link substring="System.out" target="System#out" @end region="one"
 * }
 */
public class JavaDocSnippetTest {
 
}



Javadoc Internal Snippet.png

Code compiles.
Preview Feature: Virtual Threads
Positive compilation1 (Code Snippets in Java API documentation Example) Use the following code: 
package pkg1;
 
/**
 * An example of internal Java-doc Snippet
 * {@snippet :
 *    System.out.println("Hello World"); // @highlight substring="System" type="highlighted"
 *    System.out.println("Hello World"); // @replace region="one" substring="Hello World" replacement="Hello All"
 *    System.out.println("Hello World"); // @link substring="System.out" target="System#out" @end region="one"
 * }
 */
public class JavaDocSnippetTest {
 
}



Javadoc Internal Snippet.png

Code compiles.
Incubator Feature: Structured Concurrency
Positive compilation1 (Code Snippets in Java API documentation Example) Use the following code: 
package pkg1;
 
/**
 * An example of internal Java-doc Snippet
 * {@snippet :
 *    System.out.println("Hello World"); // @highlight substring="System" type="highlighted"
 *    System.out.println("Hello World"); // @replace region="one" substring="Hello World" replacement="Hello All"
 *    System.out.println("Hello World"); // @link substring="System.out" target="System#out" @end region="one"
 * }
 */
public class JavaDocSnippetTest {
 
}



Javadoc Internal Snippet.png

Code compiles.
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