imagej/hackathon-Ostrava-2019

/**
 * A variable of type {@code T}.
 * Accessible via {@link #get()} / {@link #set(Object)}.
 * Listeners
 *
 * @author Tobias Pietzsch
 */
public class ListenableVar< T, L >
{
    private final AtomicReference< T > ref;

    private final Listeners.List< L > listeners;

    private final BiConsumer< L, T > notify;

    private final boolean notifyWhenSet;

    public ListenableVar( final T value, final Consumer< L > notify )
    {
        this( value, notify, false );
    }

    public ListenableVar( final T value, final BiConsumer< L, T > notify )
    {
        this( value, notify, false );
    }

    public ListenableVar( final T value, final Consumer< L > notify, final boolean notifyWhenSet )
    {
        this( value, ( l, t ) -> notify.accept( l ), notifyWhenSet );
    }

    public ListenableVar( final T value, final BiConsumer< L, T > notify, final boolean notifyWhenSet )
    {
        this.ref = new AtomicReference<>( value );
        this.notify = notify;
        this.notifyWhenSet = notifyWhenSet;
        this.listeners = new Listeners.SynchronizedList<>();
    }

    public void set( final T value )
    {
        final T previous = this.ref.getAndSet( value );
        if ( notifyWhenSet || !previous.equals( value ) )
            listeners.list.forEach( l -> notify.accept( l, value ) );
    }

    public T get()
    {
        return ref.get();
    }

    public Listeners< L > listeners()
    {
        return listeners;
    }

    interface ChangeListener
    {
        void changed();
    }

    interface ValueListener< T >
    {
        void valueChanged( T value );
    }

    public static void main( String[] args )
    {
        {
            ListenableVar< Integer, ChangeListener > var = new ListenableVar<>( 1, ChangeListener::changed );
            var.listeners().add( () -> System.out.println( "value changed" ) );
            var.set( 10 );
            System.out.println( "var = " + var.get() );
        }

        {
            ListenableVar< Integer, ValueListener< Integer > > var = new ListenableVar<>( 1, ValueListener::valueChanged );
            var.listeners().add( v -> System.out.println( "value changed to " + v ) );
            var.set( 10 );
            System.out.println( "var = " + var.get() );
        }
    }
}