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Java16/Examples

This is an informal page listing examples of features that are implemented by the Java 16 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:

  • Records is standard features in Java 16.
  • Instanceof Pattern Matching is also another standard features in Java 16.
  • Sealed Classes is another preview feature in Java 16. They are not enabled by default and can by enabled using --enable-preview.
  • 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: Sealed Classes
Postive compilation1 (Sealed Class Example) Use the following code: 
@SuppressWarnings("preview")
sealed class Y permits X {
}
 
@SuppressWarnings("preview")
non-sealed class X extends Y {
	public static void main(String[] args) {
		System.out.println(0);
	}
}



Sealed-class1.png

Code compiles and prints 0.
Postive compilation2 (Sealed Class Example) Use the following code: 
@SuppressWarnings("preview")
sealed interface I extends SI {
}
 
@SuppressWarnings("preview")
non-sealed class X implements SI {
	public static void main(String[] args) {
		System.out.println(0);
	}
}
 
@SuppressWarnings("preview")
sealed interface SI permits X,I {
}
 
@SuppressWarnings("preview")
non-sealed interface I2 extends I {
}



Sealed-class2.png

Code compiles and prints 0.
Postive compilation3 (Sealed Class Example) Use the following code: 
@SuppressWarnings("preview")
sealed class X permits Y {
	public static void main(String[] args) {
		System.out.println(100);
	}
}
 
@SuppressWarnings("preview")
non-sealed class Y extends X {
}



Sealed-class3.png

Code compiles and prints 100.
Postive compilation4 (Sealed Class Example) Use the following code: 
@SuppressWarnings("preview")
sealed public class X<T> {
	public static void main(String[] args) {
		System.out.println(100);
	}
}
 
@SuppressWarnings({ "preview", "rawtypes" })
non-sealed class Y extends X {
}



Sealed-class4.png

Code compiles and prints 100.
Negative compilation1 (Sealed Class Example) Use the following code: 
@SuppressWarnings("preview")
sealed public sealed class X {
	public static void main(String[] args) {
		System.out.println(100);
	}
}



Sealed-class5 BetaJava16.png

Code fails to compile with error "Multiple markers at this line

- Sealed class lacks the permits clause and no top level or nested class from the same compilation unit declares X as its direct superclass

- Duplicate modifier for the type X"

Syntax coloring for “sealed”, “non-sealed”, “permits”

Syntax-coloring.png

New restricted keywords are colored
Quick fixes support to add sealed/final/non-sealed modifier on a permitted class declaration.

Quick-fixes-3.png

Three quick fix modifier options:

- sealed

- non-sealed

- final

Quick fixes support to add sealed/non-sealed modifier on a permitted interface declaration.

Quick-fixes-2.png

Two quick fix modifier options:

- sealed

- non-sealed

"Match locations" dialog supports "Permitted type declarations"

Permitted-Type-Declarations.png

"Search > Java Search > Match locations" dialog supports "Permitted type declarations" check-box option.
Standard Feature: Records
Postive compilation1 (Record Example) Compile and run the following code: 
record Point(int x, int y) {
}
public class X1 {
	public static void main(String[] args) {
                Point p = new Point(100, 200);
		System.out.println(p.x());
	}
}
 Code compiles and prints 100.
Positive compilation2 (Nested Record Example) Compile and run the following code: 
class X2 {
	public static void main(String[] args) {
		System.out.println(0);
	}
	record Point(int x, int y) {
	}
}
 Code compiles and prints 0.
Positive compilation3 (Record Example) Compile and run the following code: 
class X3 {
	public static void main(String[] args) {
		System.out.println(0);
	}
}
final record Point(int x, int y) {
}
 Code compiles and prints 0. Though a record declaration is implicitly final, it is permitted for the declaration of a record type to redundantly specify the final modifier
Positive compilation4 Compile and run the following code: 
record R() {
}
class X4 {
	public static void main(String[] args) {
		System.out.println(new R().hashCode());
	}
}
 Code compiles and prints 0.
Positive compilation5 Compile and run the following code: 
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;
@Target({ ElementType.PARAMETER })
@interface MyAnnot {
}
record R(@MyAnnot()int i, int j) {
}
class X5 {
	public static void main(String[] args) {
		System.out.println(new R(100, 200).hashCode() != 0);
	}
}
 Code compiles and prints true.
Positive compilation6 Compile and run the following code: 
class X6 {
	public static void main(String[] args) {
		record R(int x,int y){}
		R r = new R(100, 200);
		System.out.println(r.x());
	}
}
 Code compiles and prints 100.
Negative compilation1 (Record Example) Compile and run the following code: 
abstract record Point(int x, int y){
}
class X7 {
	public static void main(String[] args){
		System.out.println(0);
	}
}
 Code fails to compile with error "Illegal modifier for the record Point; only public, final and strictfp are permitted"
Negative compilation2 (Record Example) Compile and run the following code: 
record Point1(int myInt, char myChar) implements I {
	public Point1 {
		this.myInt = myInt;
		this.myChar = myChar;
	}
}
public class X8 {
	public static void main(String[] args) {
		System.out.println(0);
	}
}
interface I {
}
 Code fails to compile with error "The canonical constructor Point1 of a record declaration must be declared public."
Negative compilation3 (Record Example) Compile and run the following code: 
class record {
	public static void main(String[] args) {
		System.out.println(0);
	}
}
 Code fails to compile with error "Record is a restricted identifier and hence not a valid type name"
Record Creation Wizard Right Click on the Project -> New -> Record or Right Click on the Project -> New -> Other and search for Record or Right Click on the Project -> New -> Other -> Java -> Record


FileAddJ15RecordCreation.png

[note: In older workspaces Record option may not appear diectly under New menu in java perspective. To resolve this, use a new workspace or relaunch eclipse with -clearPersistedState for the same workspace]

Record is created
Standard Feature: Instanceof Pattern Matching
Postive compilation1 (Instanceof Pattern Matching Example) Use the following code: 
public class X {
	public boolean isBlank(Object o) {
		return (o instanceof String s) && s.isBlank();
	}
}



Pattern-match1 BetaJava16.png

The pattern variable 's' is in current scope
Postive compilation2 (Instanceof Pattern Matching Example) Use the following code: 
public class X {
	public int size(Object obj) {
		if (obj instanceof String s) {
			return s.le
		}
		return -1;
	}
}



Pattern-match2 BetaJava16.png

The pattern variable 's' is in current scope inside 'then' statement and completion proposes applicable methods on String, the pattern matched type.
Negative compilation1 (Instanceof Pattern Matching Example) Use the following code: 
package p;
 
public class X {
	public int size(Object obj) {
		if (obj instanceof String s) {
			return s.length();
		}
		return s.length(); // s cannot be resolved
	}
}



Pattern-match3 BetaJava16.png

The pattern variable 's' is rejected by the compiler when cannot be resolved.
Negative compilation2 (Instanceof Pattern Matching Example) Use the following code: 
public class X {
	public void foo(Object obj) {
		String s = null;
		if (obj instanceof Integer s) {
		} else if (obj instanceof String) {
		}
	}
}



Pattern-match4 BetaJava16.png

The pattern variable 's' is rejected by the compiler as "Duplicate local variable s".
Retrieved from "https://wiki.eclipse.org/index.php?title=Java16/Examples&oldid=442613"

This page was last modified 02:50, 12 March 2021 by Niraj Modi.

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