win:length(2) is fired after first event - esper

Question

I made a very simple test gui based on this brilliant article about getting started with Esper.
What surprises me is that this query is validated to true after the very first tick event is sent, if the price is above 6.
select * from StockTick(symbol='AAPL').win:length(2) having avg(price) > 6.0
As far as I understand, win:length(2) needs TWO ticks before an event is fired, or am I wrong?
Here is a SSCCE for this question, just press the "Create Tick Event" button and you will see the StockTick Event being fired at once.
It needs the following jars which comes bundled with Esper
esper\lib\antlr-runtime-3.2.jar
esper\lib\cglib-nodep-2.2.jar
esper\lib\commons-logging-1.1.1.jar
esper\lib\esper_3rdparties.license
esper\lib\log4j-1.2.16.jar
esper-4.11.0.jar
import javax.swing.JFrame;
import javax.swing.JSplitPane;
import javax.swing.SwingUtilities;
import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.JButton;
import javax.swing.JScrollPane;
import java.awt.TextArea;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;
import java.util.Random;
import javax.swing.JRadioButton;
import javax.swing.JPanel;
import java.awt.GridLayout;
import javax.swing.JTextArea;
import javax.swing.ScrollPaneConstants;
import com.espertech.esper.client.Configuration;
import com.espertech.esper.client.EPAdministrator;
import com.espertech.esper.client.EPRuntime;
import com.espertech.esper.client.EPServiceProvider;
import com.espertech.esper.client.EPServiceProviderManager;
import com.espertech.esper.client.EPStatement;
import com.espertech.esper.client.EventBean;
import com.espertech.esper.client.UpdateListener;
import javax.swing.JTextField;
public class Tester extends JFrame {
/**
*
*/
private static final long serialVersionUID = 1L;
JButton createRandomValueEventButton;
private JPanel panel;
private JPanel southPanel;
private JPanel centerPanel;
private static JTextArea centerTextArea;
private static JTextArea southTextArea;
private static Random generator = new Random();
private EPRuntime cepRT;
private JSplitPane textSplitPane;
private JButton btnNewButton;
private static JTextField priceTextField;
public Tester() {
getContentPane().setLayout(new BorderLayout(0, 0));
JSplitPane splitPane = new JSplitPane();
createRandomValueEventButton = new JButton("Create Tick Event With Random Price");
splitPane.setLeftComponent(createRandomValueEventButton);
createRandomValueEventButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
createTickWithRandomPrice();
}
});
panel = new JPanel();
splitPane.setRightComponent(panel);
panel.setLayout(new GridLayout(1, 0, 0, 0));
btnNewButton = new JButton("Create Tick Event");
panel.add(btnNewButton);
btnNewButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
createTick();
}
});
priceTextField = new JTextField();
priceTextField.setText(new Integer(10).toString());
panel.add(priceTextField);
priceTextField.setColumns(4);
getContentPane().add(splitPane, BorderLayout.NORTH);
textSplitPane = new JSplitPane();
textSplitPane.setOrientation(JSplitPane.VERTICAL_SPLIT);
getContentPane().add(textSplitPane, BorderLayout.CENTER);
centerPanel = new JPanel();
centerPanel.setLayout(new BorderLayout(0, 0));
JScrollPane centerTextScrollPane = new JScrollPane();
centerTextScrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
centerTextArea = new JTextArea();
centerTextArea.setRows(12);
centerTextScrollPane.setViewportView(centerTextArea);
southPanel = new JPanel();
southPanel.setLayout(new BorderLayout(0, 0));
JScrollPane southTextScrollPane = new JScrollPane();
southTextScrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
southTextArea = new JTextArea();
southTextArea.setRows(5);
southTextScrollPane.setViewportView(southTextArea);
textSplitPane.setRightComponent(southTextScrollPane);
textSplitPane.setLeftComponent(centerTextScrollPane);
setupCEP();
}
public static void GenerateRandomTick(EPRuntime cepRT) {
double price = (double) generator.nextInt(10);
long timeStamp = System.currentTimeMillis();
String symbol = "AAPL";
Tick tick = new Tick(symbol, price, timeStamp);
System.out.println("Sending tick:" + tick);
centerTextArea.append(new Date().toString()+" Sending tick:" + tick+"\n");
cepRT.sendEvent(tick);
}
public static void GenerateTick(EPRuntime cepRT) {
double price = Double.parseDouble(priceTextField.getText());
long timeStamp = System.currentTimeMillis();
String symbol = "AAPL";
Tick tick = new Tick(symbol, price, timeStamp);
System.out.println("Sending tick:" + tick);
centerTextArea.append(new Date().toString()+" Sending tick: " + tick+"\n");
cepRT.sendEvent(tick);
}
public static void main(String[] args){
Tester tester = new Tester();
tester.setSize(new Dimension(570,500));
tester.setVisible(true);
}
private void createTickWithRandomPrice(){
SwingUtilities.invokeLater(new Runnable() {
public void run() {
GenerateRandomTick(getEPRuntime());
}
});
}
private void createTick(){
SwingUtilities.invokeLater(new Runnable() {
public void run() {
GenerateTick(getEPRuntime());
}
});
}
private void setupCEP(){
Configuration cepConfig = new Configuration();
cepConfig.addEventType("StockTick", Tick.class.getName());
EPServiceProvider cep = EPServiceProviderManager.getProvider("myCEPEngine", cepConfig);
cepRT = cep.getEPRuntime();
EPAdministrator cepAdm = cep.getEPAdministrator();
EPStatement cepStatement = cepAdm.createEPL(
"select * from " +
"StockTick(symbol='AAPL').win:length(2) " +
"having avg(price) > 6.0");
cepStatement.addListener(new CEPListener());
//System.out.println("cepStatement.getText(): "+cepStatement.getText());
}
private EPRuntime getEPRuntime(){
public static class Tick {
String symbol;
Double price;
Date timeStamp;
public Tick(String s, double p, long t) {
symbol = s;
price = p;
timeStamp = new Date(t);
}
public double getPrice() {return price;}
public String getSymbol() {return symbol;}
public Date getTimeStamp() {return timeStamp;}
#Override
public String toString() {
return symbol+" Price: " + price.toString();
}
}
public static class CEPListener implements UpdateListener {
}

Answer 1

Actually aggregation and conditions are independent of how many events are in data window. There are functions you could use to check whether a data window is "filled": the "leaving", "count" or "prevcount" for example.

Answer 2

For anyone interested,
changing the query to this solved the problem
select * from StockTick(symbol='AAPL').win:length_batch(2) having avg(price) > 6.0 and count(*) >= 2
Now an event will be triggered for every consecutive tick with the price higher than 6, in batches of two.