Exploring Properties and Threads in JavaFx for StackOverflow Question https://stackoverflow.com/questions/38001595/javafx-only-update-binding-after-all-dependencies-are-updated

PropertiesWithThreads.java

package com.isp.stackoverflow;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadLocalRandom;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.binding.Bindings;
import javafx.beans.binding.ObjectBinding;
import javafx.beans.property.Property;
import javafx.beans.property.SimpleObjectProperty;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Separator;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

/**
 * https://stackoverflow.com/questions/38001595/javafx-only-update-binding-after-all-dependencies-are-updated
 *
 * @author okr
 * @date 24.06.2016
 *
 */
public class PropertiesWithThreads extends Application
{
  private final ExecutorService           executor       = Executors.newFixedThreadPool( 2 );

  private final Property<BigDecimal>      a              =
      new SimpleObjectProperty<>( newRandomBigDecimal( ThreadLocalRandom.current(), 10 ) );
  private final Property<BigDecimal>      b              =
      new SimpleObjectProperty<>( newRandomBigDecimal( ThreadLocalRandom.current(), 10 ) );

  private final Task<Void>                taskAB         = new Task<Void>()
                                                         {

                                                           @Override
                                                           protected Void call() throws Exception
                                                           {
                                                             while ( !isCancelled() )
                                                             {
                                                               Thread.sleep( 2000 );
                                                               System.out.println( "Updating A!" );
                                                               Platform.runLater( () -> a
                                                                   .setValue( newRandomBigDecimal( ThreadLocalRandom.current(), 10 ) ) );
                                                               Thread.sleep( 2000 );
                                                               System.out.println( "Updating B!" );
                                                               Platform.runLater( () -> b
                                                                   .setValue( newRandomBigDecimal( ThreadLocalRandom.current(), 10 ) ) );
                                                             }
                                                             return null;
                                                           }
                                                         };


  private final ObjectBinding<BigDecimal> c              = new ObjectBinding<BigDecimal>()
                                                         {
                                                           {
                                                             super.bind( a, b );
                                                           }

                                                           @Override
                                                           protected BigDecimal computeValue()
                                                           {
                                                             return a.getValue().add( b.getValue() );
                                                           }
                                                         };

  private final ObjectBinding<BigDecimal> cOnlyOnBChange = new ObjectBinding<BigDecimal>()
                                                         {
                                                           {
                                                             super.bind( b );
                                                           }

                                                           @Override
                                                           protected BigDecimal computeValue()
                                                           {
                                                             return a.getValue().add( b.getValue() );
                                                           }
                                                         };

  private final Task<Void>                taskC          = new Task<Void>()
                                                         {
                                                           @Override
                                                           protected Void call() throws Exception
                                                           {
                                                             cOnlyOnBChange.addListener( ( __, ___, newValue ) -> System.out
                                                                 .println( "C changed to " + newValue ) );
                                                             return null;
                                                           }
                                                         };

  BigDecimal getC()
  {
    return c.getValue();
  }

  private static BigDecimal newRandomBigDecimal( final Random random, final int precision )
  {
    final BigInteger n = BigInteger.TEN.pow( precision );
    return new BigDecimal( newRandomBigInteger( n, random ), precision );
  }

  private static BigInteger newRandomBigInteger( final BigInteger n, final Random random )
  {
    BigInteger r;
    do
    {
      r = new BigInteger( n.bitLength(), random );
    } while ( r.compareTo( n ) >= 0 );

    return r;
  }

  @Override
  public void start( final Stage primaryStage )
  {
    final Label labelA = new Label();
    final Label labelB = new Label();
    final Label labelC = new Label();

    labelA.textProperty().bind( Bindings.format( "A = %s", a ) );
    labelB.textProperty().bind( Bindings.format( "B = %s", b ) );
    labelC.textProperty().bind( Bindings.format( "C = %s", c ) );

    final VBox root = new VBox( 16, labelA, labelB, new Separator(), labelC );
    primaryStage.setScene( new Scene( root ) );
    primaryStage.show();

    executor.execute( taskAB );
    executor.execute( taskC );

    primaryStage.setOnCloseRequest( __ ->
    {
      executor.shutdownNow();
      primaryStage.close();
    } );
  }

  /**
   * @param args ignore.
   */
  public static void main( final String[] args )
  {
    launch( args );
  }
}