CASCalculator.java

package main;

import java.util.concurrent.atomic.AtomicReference;

public class CASCalculator extends CalculatorBase {

    private enum Status {
        NOT_STARTED,
        STARTED,
        DISPOSED
    }

    private AtomicReference<Status> status = new AtomicReference<Status>(Status.NOT_STARTED);

    @Override
    public void start() {
        if (status.compareAndSet(Status.NOT_STARTED, Status.STARTED)) {
            startCore();
        }
        // Do something useful, calculator is started now.
    }

    @Override
    public void dispose() {
        if (status.compareAndSet(Status.STARTED, Status.DISPOSED)) {
            disposeCore();
            // Do something useful, calculator is disposed now.
        } else {
            // Calculator is not started yet or has been disposed.
        }
    }
}