Sealed classes, interfaces and records

Sealed classes, interfaces work well with records. To demonstrate the example, I am defining a sealed interface Operation, and two record types Add, Mul will implement this sealed interface.

 

Operation.java

package com.sample.app.recrods;

public sealed interface Operation permits Add, Mul{

    public Long operation();
}

Add.java

package com.sample.app.recrods;

public record Add(int... a) implements Operation {

    @Override
    public Long operation() {
        if(a == null || a.length == 0) {
            return null;
        }
        
        long sum = 0;
        
        for(int ele : a) {
            sum += ele;
        }
        
        return sum;
    }

}

Mul.java

package com.sample.app.recrods;

public record Mul(int... a) implements Operation {

    @Override
    public Long operation() {
        if (a == null || a.length == 0) {
            return null;
        }

        long result = 1;

        for (int ele : a) {
            result *= ele;
        }

        return result;
    }

}

SealedAndRecordDemo.java

package com.sample.app;

import com.sample.app.recrods.Add;
import com.sample.app.recrods.Mul;

public class SealedAndRecordDemo {

    public static void main(String[] args) {
        Add add = new Add(new int[] { 2, 3, 5, 7 });
        Mul mul = new Mul(new int[] { 2, 3, 5, 7 });

        System.out.println("Sum of first four primes : %d".formatted(add.operation()));
        System.out.println("Multiplication of first four primes : %d".formatted(mul.operation()));
    }

}

Output

Sum of first four primes : 17
Multiplication of first four primes : 210

 

References

https://openjdk.org/jeps/360

https://openjdk.org/jeps/384

 

 

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Java15: Sealed interfaces

This is continuation to my previous post ‘sealed classes’, I would request you to go through the previous post before reading this.

 

Sealed classes and interfaces specify who can extend or implement this class or interface. A sealed class or interface can be extended or implemented only by those classes and interfaces permitted to do so.

 

A interface is sealed by applying the sealed modifier to its declaration. For example, the following declaration declare a sealed interface EmployeeService which permits two classes (PermanentEmployeeServiceImpl,TemporaryEmployeeServiceImpl) to implement it.

 

EmployeeService.java

package com.sample.app.interfaces.sealed;

public sealed interface EmployeeService permits PermanentEmployeeServiceImpl,TemporaryEmployeeServiceImpl {

}

 

PermanentEmployeeServiceImpl.java

package com.sample.app.interfaces.sealed;

public final class PermanentEmployeeServiceImpl implements EmployeeService{

}

 

TemporaryEmployeeServiceImpl.java

package com.sample.app.interfaces.sealed;

public final class TemporaryEmployeeServiceImpl implements EmployeeService{

}

 

Where to specify the permit clause, if my interface extends another interfaces?

After any extends clause to specify superinterfaces, the implementing classes and subinterfaces are specified with a permits clause. 

public sealed interface PersonInterface extends Serializable permits PersonImpl, UserImpl{

}

  

References

https://openjdk.org/jeps/360

 

 

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