Java – Silico Sciences

sort a Set

Q: How to sort an instance of java.util.Set?

Set<String> set = new HashSet<>();
List<String> list = new ArrayList<>();
list.addAll(set);
Collections.sort(list);
// sorted by insertion order
Set<String> sortedSet = new LinkedHashSet<>();
sortedSet.addAll(list);
// sorted by natural ordering of elements (need to implement Comparable)
// or by given Comparator
Set<String> sortedTreeSet = new TreeSet<>();
// we can add the unsorted set, will be sorted automatically each time
// when modifying
sortedTreeSet.addAll(set);

Set<String> set = new HashSet<>();

List<String> list = new ArrayList<>();

list.addAll(set);

Collections.sort(list);

// sorted by insertion order

Set<String> sortedSet = new LinkedHashSet<>();

sortedSet.addAll(list);

// sorted by natural ordering of elements (need to implement Comparable)

// or by given Comparator

Set<String> sortedTreeSet = new TreeSet<>();

// we can add the unsorted set, will be sorted automatically each time

// when modifying

sortedTreeSet.addAll(set);

See a more detailed explanation here.

run a backtest using the JForex API (v. 2.x)

Create a client instance

final ITesterClient testerClient = TesterFactory.getDefaultInstance();

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final ITesterClient testerClient = TesterFactory.getDefaultInstance();
Register event listeners

testerClient.setSystemListener(new MySystemListener();

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testerClient.setSystemListener(new MySystemListener();
Connect the client

testerClient.connect("http://platform.dukascopy.com/demo/jforex.jnlp", username, password);

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testerClient.connect("http://platform.dukascopy.com/demo/jforex.jnlp", username, password);

Configure the time period to backtest

final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd-HH:mm:ss");
dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
final Date dateFrom = dateFormat.parse("2013-01-01-12:00:00");
final Date dateTo = dateFormat.parse("2013-02-01-12:00:00");
testerClient.setDataInterval(DataLoadingMethod.ALL_TICKS, dateFrom.getTime(), dateTo.getTime());

final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd-HH:mm:ss");

dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));

final Date dateFrom = dateFormat.parse("2013-01-01-12:00:00");

final Date dateTo = dateFormat.parse("2013-02-01-12:00:00");

testerClient.setDataInterval(DataLoadingMethod.ALL_TICKS, dateFrom.getTime(), dateTo.getTime());

Configure the instrument

testerClient.setSubscribedInstruments(new LinkedHashSet<>(Arrays.asList(Instrument.EURUSD)));

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testerClient.setSubscribedInstruments(new LinkedHashSet<>(Arrays.asList(Instrument.EURUSD)));
Start the Backtest

final long processId = testerClient.startStrategy(myStrategy);

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final long processId = testerClient.startStrategy(myStrategy);

Get more info here: Dukaskopy Knowledge Base

maintain library project for Maven and Eclipse RCP/ OSGi in the same repository

If you are working both in the Maven and the Eclipse RCP/ OSGi universe, you might find it quite frustrating that these two worlds cooperate so poorly. In order to use the same library in both worlds, a lot of error-prone copy-and-paste is needed, at least if you would like to use this project in a Maven and Maven Tycho build.

In principle, there is not much that is different for a Maven artifact and an Eclipse RCP/ OSGi Plug-in:
In an Eclipse RCP/ OSGi Plug-in you just need an additional META-INF/MANIFEST.MF and build.properties file. The problem comes with the Maven pom file, which looks completely different for standard Maven and Maven Tycho. Luckily, you can specify the name of the pom file when invoking Maven:

mvn -f <other pom file>

1	mvn -f <other pom file>

Therefore, you can just maintain two pom files and with only few limitations, it is possible to maintain a library that can be used in a standard Maven build and in a Maven Tycho build within the same repository:

Modify your .gitignore so that it contains the following lines:
```
bin
.project
.settings
.classpath
```
We don’t want to have any Eclipse project configuration information in the project, since we want to be able to import it both as ‘Maven project’ and ‘Eclipse/ OSGi project’.
Remove all files from the git index that match the pattern above.

Shell

$ git rm --cached .classpath .project $ git rm --cached -r .settings/

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$ git rm --cached .classpath .project
$ git rm --cached -r .settings/
- If your project is a Maven project, right-click on the project and select ‘Configure -> Convert to Plug-in project’. This will create the META-INF/MANIFEST.MF and build.properties files.
- If your project is a Plug-in project, right-click on the project and select ‘Configure -> Convert to Maven project’. This will create the pom.xml file.
These steps are optional and only needed if you are missing either pom.xml or META-INF/MANIFEST.MF and build.properties .

Create the Tycho pom file, name it e.g. pom-tycho.xml. It’s content should look like this:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>	
	<groupId>net.sf.kerner</groupId>
	<artifactId>net.sf.kerner.utils</artifactId>
	<version>1.3.1-SNAPSHOT</version>
	<packaging>eclipse-plugin</packaging>
</project>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<groupId>net.sf.kerner</groupId>

<artifactId>net.sf.kerner.utils</artifactId>

<version>1.3.1-SNAPSHOT</version>

<packaging>eclipse-plugin</packaging>

</project>

Commit all changes and delete the project from your workspace.
Import the project using the ‘Import Existing Maven Project’ or ‘Checkout Maven Project from scm’ wizard. To use the project as an Eclipse RCP/ OSGi Plug-in project, disable it’s Maven nature via ‘Maven -> disable Maven nature’.
Done!

Note: You manually need to keep in sync the version strings in pom.xml, META-INF/MANIFEST.MF and pom-tycho.xml! E.g. after running a Maven release, you need to adapt the version numbers in META-INF/MANIFEST.MF and pom-tycho.xml so that they match the automatically changed version strings in pom.xml.
Also note that you cannot use a Bundle Activator in this project. If you need one, just create another Eclipse-RCP Plug-in that depends on your library and contains a Bundle Activator.

Troubleshooting: After importing as Maven project or converting to Maven project, you might run into build-path problems. Try to resolve using ‘right-click on project -> Maven -> Update Project..’ And/ or fix the Java Build Path of the project (Standard Eclipse source folder is src, in Maven it is src/main/java).

change file encoding recursively

Good:

find . -name "*.java" -exec iconv -f windows-1252 -t utf-8 {} -o {}.utf8 \;

1	find . -name "*.java" -exec iconv -f windows-1252 -t utf-8 {} -o {}.utf8 \;

Bad:

find . -name "*.java" -exec iconv -f windows-1252 -t utf-8 {} -o converted/{} \;

1	find . -name "*.java" -exec iconv -f windows-1252 -t utf-8 {} -o converted/{} \;

The second one will only work if find will not descend into sub directories, since the directory tree inside of converted will not be created on demand, as it would be the case e.g. for mkdir -p. The result will be a ‘file or directory not found’ error.

OrientDB Document API best practices

OrientDB is an open source NoSQL Database Managment System, which supports multiple models of operation:

Document Model,
Graph Model
Object Model.

We will write here about the Document Model. It is the most low-level of the three models and and can provide great performance if no graph or object model is needed. Nevertheless, using a document-based database requires different programming patterns than the ones you know already from the world of object-oriented programming. We will try to compose some best-practices and programming patterns here to guide you when working with document-based database systems in general and the usage of the OrientDB Document API in particular.

Performance and Threading
ODocument is not thread save. It is not intended to be accessed by multiple threads at the same time. Accessing the db using multiple instances of ODatabaseDocumentTx nevertheless is thread save.

Anti-Pattern

private static String dbString = "testData/databases/TestCaseDB4";
ODatabaseDocumentTx documentDatabase = new ODatabaseDocumentTx("plocal:" + dbString, true);
documentDatabase.open("admin", "admin");
List<ODocument> manyManyDocuments = getManyDocuments();
manyManyDocuments.parallelStream().forEach(a -> a.field("someFieldID", "newValue"));

private static String dbString = "testData/databases/TestCaseDB4";

ODatabaseDocumentTx documentDatabase = new ODatabaseDocumentTx("plocal:" + dbString, true);

documentDatabase.open("admin", "admin");

List<ODocument> manyManyDocuments = getManyDocuments();

manyManyDocuments.parallelStream().forEach(a -> a.field("someFieldID", "newValue"));

Pattern

private static String dbString = "testData/databases/TestCaseDB4";
OPartitionedDatabasePool pool = new OPartitionedDatabasePool("plocal:" + dbString, "admin", "admin");
List<ODocument> manyManyDocuments = getManyDocuments();
manyManyDocuments.parallelStream().forEach(a -> {
ODatabaseDocumentTx documentDatabase = null;
try {
	ODatabaseDocumentTx documentDatabase = pool.acquire();
	a.field("someFieldID", "newValue");
} finally {
	if(documentDatabase != null) {
		documentDatabase.close();
	}
}
});

private static String dbString = "testData/databases/TestCaseDB4";

OPartitionedDatabasePool pool = new OPartitionedDatabasePool("plocal:" + dbString, "admin", "admin");

List<ODocument> manyManyDocuments = getManyDocuments();

manyManyDocuments.parallelStream().forEach(a -> {

ODatabaseDocumentTx documentDatabase = null;

try {

ODatabaseDocumentTx documentDatabase = pool.acquire();

a.field("someFieldID", "newValue");

} finally {

if(documentDatabase != null) {

documentDatabase.close();

}

});

Explanations
Note that documentDatabase itself is not used. ODocument accesses the document database via a thread-local, static instance of ODatabaseDocumentInternal.

public abstract class ORecordAbstract implements ORecord {
    [..]
    public ODatabaseDocumentInternal getDatabase() {
        return ODatabaseRecordThreadLocal.INSTANCE.get();
    }
    [..]
}

public abstract class ORecordAbstract implements ORecord {

[..]

public ODatabaseDocumentInternal getDatabase() {

return ODatabaseRecordThreadLocal.INSTANCE.get();

}

[..]

}

Consistently, it is required to set this thread-local instance in each thread that is running on the ODocument class.

public class OPartitionedDatabasePool extends OOrientListenerAbstract {
    [..]
    public ODatabaseDocumentTx acquire() {
        [..]
        data.acquiredDatabase.activateOnCurrentThread();
        return data.acquiredDatabase;
    }
    [..]
}

public class OPartitionedDatabasePool extends OOrientListenerAbstract {

[..]

public ODatabaseDocumentTx acquire() {

[..]

data.acquiredDatabase.activateOnCurrentThread();

return data.acquiredDatabase;

}

[..]

}

public ODatabaseDocumentTx(final String iURL, boolean keepStorageOpen) {
    super(false);
    activateOnCurrentThread();
    [..]
}

public ODatabaseDocumentTx(final String iURL, boolean keepStorageOpen) {

super(false);

activateOnCurrentThread();

[..]

}

To be continued

trigger dependency injection from any class

If you need an injectable service, such as the IEventBroker, in a class that is not subject to DI per default, you can trigger DI manually:

MyPoJoClass {

@Inject
private IEventBroker eventBroker;

public MyPoJoClass {
inject();
}

private void inject() {
IEclipseContext serviceContext = EclipseContextFactory.getServiceContext(Activator.getContext());
ContextInjectionFactory.inject(this, serviceContext);
}

private void inject2() {
IEclipseContext serviceContext = EclipseContextFactory.getServiceContext(Activator.getDefault().getBundle().getBundleContext());
ContextInjectionFactory.inject(this, serviceContext);
}

public void fireSomeEvents(Object data){
eventBroker.publish("My_Event", data)
}
}

MyPoJoClass {

@Inject

private IEventBroker eventBroker;

public MyPoJoClass {

inject();

}

private void inject() {

IEclipseContext serviceContext = EclipseContextFactory.getServiceContext(Activator.getContext());

ContextInjectionFactory.inject(this, serviceContext);

}

private void inject2() {

IEclipseContext serviceContext = EclipseContextFactory.getServiceContext(Activator.getDefault().getBundle().getBundleContext());

ContextInjectionFactory.inject(this, serviceContext);

}

public void fireSomeEvents(Object data){

eventBroker.publish("My_Event", data)

}

Eclipse RCP e4 and JavaFX: minimal working example

Install Java 8

Install JavaFX Tooling and Runtime for Eclipse and OSGi

Make sure Java8 is selected as the default JRE.

Create a new Eclipse 4 application project.

Make sure you select Create sample content (parts, menu etc.).

The e4 application.

Create a new class, FXMLController, with the following content:

package parts;

import java.net.URL;
import java.util.ResourceBundle;

import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.chart.AreaChart;
import javafx.scene.chart.XYChart;

public class FXMLController implements Initializable {

	@FXML
	private AreaChart areaChart;
	private XYChart.Series series;

	private void createChart() {

		series = new XYChart.Series();

		for (int i = 0; i < 100; i++) {
			series.getData().add(new XYChart.Data(i, Math.random()));
		}

		areaChart.getData().addAll(series);
	}

	@Override
	public void initialize(URL url, ResourceBundle rb) {

		createChart();
	}
}

package parts;

import java.net.URL;

import java.util.ResourceBundle;

import javafx.fxml.FXML;

import javafx.fxml.Initializable;

import javafx.scene.chart.AreaChart;

import javafx.scene.chart.XYChart;

public class FXMLController implements Initializable {

@FXML

private AreaChart areaChart;

private XYChart.Series series;

private void createChart() {

series = new XYChart.Series();

for (int i = 0; i < 100; i++) {

series.getData().add(new XYChart.Data(i, Math.random()));

}

areaChart.getData().addAll(series);

}

@Override

public void initialize(URL url, ResourceBundle rb) {

createChart();

}

Create a new file, fxml/FXML.fxml, with the following content:

<?xml version="1.0" encoding="UTF-8"?>
 
<?import java.lang.*?>
<?import java.net.*?>
<?import java.util.*?>
<?import javafx.scene.chart.*?>
<?import javafx.geometry.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
 
<AnchorPane id="AnchorPane" prefHeight="400.0" prefWidth="600.0" styleClass="mainFxmlClass" xmlns:fx="http://javafx.com/fxml/1" fx:controller="parts.FXMLController">
    <stylesheets>
        <URL value="@/styles/fxml.css"/>
    </stylesheets>
    <children>
        <AreaChart fx:id="areaChart" title="TIC"  layoutX="10" layoutY="10" AnchorPane.bottomAnchor="10.0" AnchorPane.leftAnchor="10.0" AnchorPane.rightAnchor="10.0" AnchorPane.topAnchor="10.0">
            <xAxis>
                <NumberAxis side="BOTTOM" />
            </xAxis>
            <yAxis>
                <NumberAxis side="LEFT" />
            </yAxis>
        </AreaChart>
    </children>
</AnchorPane>

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>

<?import java.net.*?>

<?import java.util.*?>

<?import javafx.scene.chart.*?>

<?import javafx.geometry.*?>

<?import javafx.scene.*?>

<?import javafx.scene.control.*?>

<?import javafx.scene.layout.*?>

</stylesheets>

<xAxis>

</xAxis>

<yAxis>

</yAxis>

</AreaChart>

</children>

</AnchorPane>

Create a new file, styles/fxml.css, with the following content:

CSS

/* * Empty Stylesheet file. */ .mainFxmlClass { }

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/*
* Empty Stylesheet file.
*/

.mainFxmlClass {

}

Open SamplePart.java and replace its content with the following:

package parts;

import java.net.URL;

import javax.annotation.PostConstruct;

import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Composite;

import javafx.application.Platform;
import javafx.embed.swt.FXCanvas;
import javafx.fxml.FXMLLoader;
import javafx.fxml.JavaFXBuilderFactory;
import javafx.scene.Parent;
import javafx.scene.Scene;

public class SamplePart {

	private FXMLController controller;

	private FXCanvas fxCanvas;

	@PostConstruct
	public void createComposite(Composite parent) {

		init(parent);
	}

	private void createScene() {

		System.out.println("Initializing FX");

		try {
			final URL location = getClass().getResource("/fxml/FXML.fxml");
			final FXMLLoader fXMLLoader = new FXMLLoader();
			fXMLLoader.setLocation(location);
			fXMLLoader.setBuilderFactory(new JavaFXBuilderFactory());
			final Parent root = fXMLLoader.load(location.openStream());
			final Scene scene = new Scene(root);
			scene.getStylesheets().add("/styles/fxml.css");
			fxCanvas.setScene(scene);
			controller = fXMLLoader.getController();

			System.out.println("Initializing FX successful");

		} catch (final Exception e) {
			e.printStackTrace();
		}
	}

	private void init(Composite parent) {

		// this will initialize the FX Toolkit
		fxCanvas = new FXCanvas(parent, SWT.NONE);

		Platform.setImplicitExit(false);
		Platform.runLater(() -> createScene());
	}
}

package parts;

import java.net.URL;

import javax.annotation.PostConstruct;

import org.eclipse.swt.SWT;

import org.eclipse.swt.widgets.Composite;

import javafx.application.Platform;

import javafx.embed.swt.FXCanvas;

import javafx.fxml.FXMLLoader;

import javafx.fxml.JavaFXBuilderFactory;

import javafx.scene.Parent;

import javafx.scene.Scene;

public class SamplePart {

private FXMLController controller;

private FXCanvas fxCanvas;

@PostConstruct

public void createComposite(Composite parent) {

init(parent);

}

private void createScene() {

System.out.println("Initializing FX");

try {

final URL location = getClass().getResource("/fxml/FXML.fxml");

final FXMLLoader fXMLLoader = new FXMLLoader();

fXMLLoader.setLocation(location);

fXMLLoader.setBuilderFactory(new JavaFXBuilderFactory());

final Parent root = fXMLLoader.load(location.openStream());

final Scene scene = new Scene(root);

scene.getStylesheets().add("/styles/fxml.css");

fxCanvas.setScene(scene);

controller = fXMLLoader.getController();

System.out.println("Initializing FX successful");

} catch (final Exception e) {

e.printStackTrace();

}

private void init(Composite parent) {

// this will initialize the FX Toolkit

fxCanvas = new FXCanvas(parent, SWT.NONE);

Platform.setImplicitExit(false);

Platform.runLater(() -> createScene());

}

Open META-INF/MANIFEST.MF and add org.eclipse.fx.javafx and org.eclipse.fx.osgi.util to Required Plug-ins.
Open e4-javafx.product and add the following to the VM Arguments:
```
-Dosgi.framework.extensions=org.eclipse.fx.osgi
```
Launch the application:

Exception vs. RuntimeException

An Exception indicates a user’s error (FileNotFoundException), while a RuntimeException indicates a Programmer’s Error (IllegalStateException, UnsupportedOperationException).

Checked vs. Unchecked Exceptions

Use checked exceptions for recoverable conditions and runtime exceptions for programming errors.
Joshua Bloch, Effective Java

This might be a little abstract, so we to concretize to
User’s error vs. Programmer’s error.

RuntimeException and all its child classes indicate a programmer’s error, while Exception and all its child classes indicate a user’s error:

FileNotFoundException: Can happen anytime, its not a programmer’s mistake but a user’s error (choose a wrong file, working with a read-only or full file system, etc.)
SQLException: Something went wrong with the database operation. Try to recover or notify the user. This example fits very good to the above mentioned ‘recoverable’ condition but can be as well caused by a user’s error, e.g. an invalid search query.
NullPointerException: Clearly a programmer’s error, don’t catch it but make it not happen.
ArithmeticException: Happens for example when you divide by zero. A programmer’s error. Don’t divide by zero.
UnsupportedOperationException: Thrown for example by immutable implementations of Collection (e.g. Collections.unmodifiableList()). It’s the responsibility of the programmer to handle this case.

Maven: pass pom.xml as a parameter

mvn clean install -f libraries/modules/module1/pom.xml