Now Java Developer can write their 'Will' [JDK15 JEP 360: Sealed Class (Preview)]

As a developer if you want to control who can extend your class or interface. 

In this enhancement of Java programming language, new keywords are introduced sealed, non-sealed and permit at the class level. 

A sealed class or interface can be extended or implemented only by those classes and interfaces permitted to do so. If you try to implement or extend to other class which is not permitted then the code will not compile. For example,

public sealed class Point permits Line

A permit keyword defines which are the subclasses or interfaces can be extended or implemented from this class. For example, 

public sealed class Point permits Line

Point class only permits Line class to extend directly. 

A non-sealed class or interface will allow this class to be extended. 

For example,

public non-sealed class Line

Permitted class Line is open for any unknown class extension. 

	public sealed class Shape permits Circle {
	public void name() {
	System.out.println("This is Shape.");
	}
	public static void main(String args[]) {
	Shape shape = new Shape();
	shape.name();
	Shape newShape = new Circle();
	newShape.name();
	}
	}
	non-sealed class Circle extends Shape {
	@Override
	public void name() {
	System.out.println("This is Circle.");
	}
	}

view raw Shape.java hosted with ❤ by GitHub

To Compile

To Run

A permitted subclass must define whether it could be extended to a specific class (sealed) or open to any unknown class(non-sealed) or not open for any extension (final). 

When a not permitted class extend a sealed class. 

Happy Coding and keep learning!

JDK 15 [Pattern Matching of instanceof operator ]

This is an enhancement of Java language with pattern matching for the instanceof operator. Currently, this feature is in the second preview in JDK 15.

So currently when we need to cast an object, we check it using instanceof operation then only we cast the object to save our self from class cast exception.

In the above code snippet, we have to explicitly cast it to an object. 

In this enhancement, we no more have to do it. 

To run the below code you need to install JDK 14 or above and have to enable the preview feature of javac & java. 

In order to enable that preview feature. 

javac 

      --enable-preview 

        -release <version> 

      <Source file>

java 

    --enable-preview 

       <Compiled class> 

	// Anindya Bandopadhyay (anindyabandopadhyay@gmail.com)
	public class PatternMatchingOfInstance {
	public static void main(final String args[]) {
	PatternMatchingOfInstance instance = new PatternMatchingOfInstance();
	Object obj = instance.getValue((instance.new IntValue(1)));
	if(obj instanceof Integer) {
	final Integer intValue = (Integer) obj;
	System.out.println(String.format("Int value = %d", intValue));
	}
	//JEP 375: Pattern Matching for instanceof (Second Preview)
	if(obj instanceof Integer objInt) {
	System.out.println(String.format("Using Pattern Matching for instanceof: Int value = %d", objInt));
	}
	}
	private Object getValue(final Value value) {
	return value.getValue();
	}
	interface Value {
	Object getValue();
	}
	class IntValue implements Value {
	private final int value;
	public IntValue(final int value) {
	this.value = value;
	}
	@Override
	public Integer getValue() {
	return value;
	}
	}
	class BoolValue implements Value {
	private final boolean value;
	public BoolValue(final boolean value) {
	this.value = value;
	}
	@Override
	public Boolean getValue() {
	return value;
	}
	}
	class StrValue implements Value {
	private final String value;
	public StrValue(final String value) {
	this.value = value;
	}
	@Override
	public String getValue() {
	return value;
	}
	}
	class DoubleValue implements Value {
	private final double value;
	public DoubleValue(final double value) {
	this.value = value;
	}
	@Override
	public Double getValue() {
	return value;
	}
	}
	class FloatValue implements Value {
	private final float value;
	public FloatValue(final float value) {
	this.value = value;
	}
	@Override
	public Float getValue() {
	return value;
	}
	}
	}

view raw PatternMatchingOfInstance.java hosted with ❤ by GitHub

Output

 Happy Coding!