Investor – A Java Quantitative Trading Library

Investor – A Java Quantitative Trading Library

Published by pschatzmann on 30. May 2018

Introduction

Last year I was busy to build my own project which provides an easy to use functionality to implement and evaluate automatic stock trading strategies. It is implemented in java and therefore can be used in any environment which builds on the JVM.

It provides the following functionality:
– Simple access to stock data
– Declarative formulation of trading strategies
– Evaluation of trading strategies
– Optimization of trading strategies
– Support of portfolio of multiple stocks / trading strategies

At the end it should be possible to easily formulate and evaluate stock strategy and to evaluate the impact of changes on assumptions.

In this document we demonstrates the basic functionality using Scala: We are using JupyterLab with the BeakerX Scala Kernel. The Jupyter source code can be found on github. And finally here is the link to the Javadoc.

Setup

We need to add the java libraries:

%classpath config resolver maven-public http://software.pschatzmann.ch/repository/maven-public/
%classpath add mvn ch.pschatzmann:investor:0.9-SNAPSHOT
%classpath add mvn ch.pschatzmann:jupyter-jdk-extensions:0.0.1-SNAPSHOT

Added new repo: maven-public

Imports

First we define all the imports which are used in this demo:

// our stock evaluation framwork
import ch.pschatzmann.dates._;
import ch.pschatzmann.stocks._;
import ch.pschatzmann.stocks.data.universe._;
import ch.pschatzmann.stocks.input._;
import ch.pschatzmann.stocks.accounting._;
import ch.pschatzmann.stocks.accounting.kpi._;
import ch.pschatzmann.stocks.execution._;
import ch.pschatzmann.stocks.execution.fees._;
import ch.pschatzmann.stocks.execution.price._;
import ch.pschatzmann.stocks.parameters._;
import ch.pschatzmann.stocks.strategy._;
import ch.pschatzmann.stocks.strategy.optimization._;
import ch.pschatzmann.stocks.strategy.allocation._;
import ch.pschatzmann.stocks.strategy.selection._;
import ch.pschatzmann.stocks.integration._;
import ch.pschatzmann.stocks.integration.ChartData.FieldName._;
import ch.pschatzmann.stocks.strategy.OptimizedStrategy.Schedule._;


// java
import java.util.stream.Collectors;
import java.util._;
import java.lang._;
import java.util.function.Consumer;

// ta4j
import org.ta4j.core._;
import org.ta4j.core.analysis._;
import org.ta4j.core.analysis.criteria._;
import org.ta4j.core.indicators._;
import org.ta4j.core.indicators.helpers._;
import org.ta4j.core.trading.rules._;

// jupyter custom displayer
import ch.pschatzmann.display.Displayers

import ch.pschatzmann.dates._
import ch.pschatzmann.stocks._
import ch.pschatzmann.stocks.data.universe._
import ch.pschatzmann.stocks.input._
import ch.pschatzmann.stocks.accounting._
import ch.pschatzmann.stocks.accounting.kpi._
import ch.pschatzmann.stocks.execution._
import ch.pschatzmann.stocks.execution.fees._
import ch.pschatzmann.stocks.execution.price._
import ch.pschatzmann.stocks.parameters._
import ch.pschatzmann.stocks.strategy._
import ch.pschatzmann.stocks.strategy.optimization._
import ch.pschatzmann.stocks.strategy.allocation._
import ch.pschatzmann.stocks.strategy.selection._
import ch.pschatzmann.stocks.integration._
import ch.pschatzmann.stocks.integration.ChartData.FieldName._
import ch.pschatzmann.stocks.strategy.OptimizedStrategy.Schedule._
import java.util.stream...

We register the automatic displayers for charts. We are also not interested in information messages from the log, so we define a higher log level:

Displayers.setup("WARN")

true

Basic Data Structures: Universe, StockID, StockData

A StockID is identifiying a stock by the trading symbol and the exchange.

The Uninverse is a collection of StockIDs. We can use the universe to find stocks or to process a collection relevant stocks.
– QuandlWIKIUniverse
– QuandlSixUniverse
– QuandlEuronextUniverse
– MarketUniverse
– JsonUniverse
– ListUniverse

var universe = new ListUniverse(Arrays.asList(new StockID("AAPL","NASDAQ")));
var values = universe.list();

Displayers.display(values)

ticker	exchange
AAPL	NASDAQ

var universe = new QuandlSixUniverse();
var values = Context.head(universe.list(),10);

Displayers.display(values)

ticker	exchange
ARP290071876CHF	SIX
AN8068571086CHF	SIX
AT0000652011CHF	SIX
AT0000741053CHF	SIX
AT0000606306CHF	SIX
AT0000676903CHF	SIX
AT0000743059CHF	SIX
AT0000644505CHF	SIX
AT0000720008CHF	SIX
AT0000697750CHF	SIX

Just as a side note: The API provides java collections. It is possible to convert them to a Scala type – e.q a Seq.

var universe = new IEXUniverse();
var values = Context.head(universe.list(),10);

Displayers.display(values)

ticker	exchange
A
AA
AABA
AAC
AADR
AAL
AAMC
AAME
AAN
AAOI

import scala.collection.JavaConverters;

JavaConverters.asScalaBufferConverter(values).asScala.toSeq

[[:A, :AA, :AABA, :AAC, :AADR, :AAL, :AAMC, :AAME, :AAN, :AAOI]]

The StockData is the class which provides the history of stock rates and some stock related KPIs. We need to indicate a Reader which defines the source of the data.

Currently we support
– YahooReader
– QuandlWIKIReader
– QuandlSixReader
– MarketArchiveHttpReader
– AlphaVantageReader
– IEXReader

Here is the example how to retrieve the stock history:

var stockdata = new StockData(new StockID("AAPL", "NASDAQ"), new IEXReader());

Displayers.display(Context.tail(stockdata.getHistory(),10));

index	date	low	high	open	closing	adjustmentFactor	volume
1248	2018-05-14	187.86		189.01	188.15		20778772
1249	2018-05-15	185.1		186.78	186.44		23695159
1250	2018-05-16	186		186.07	188.18		19183064
1251	2018-05-17	186.36		188	186.99		17294029
1252	2018-05-18	186.13		187.19	186.31		18297728
1253	2018-05-21	186.9106		188	187.63		18400787
1254	2018-05-22	186.78		188.375	187.16		15240704
1255	2018-05-23	185.76		186.35	188.36		20058415
1256	2018-05-24	186.21		188.77	188.15		23233975
1257	2018-05-25	187.65		188.23	188.58		17460963

Charts

Unfortunatly the BeakerX charting currently does not work in Jupyterlab. Therfore we use JFeeChart http://www.jfree.org/jfreechart/.

Now, we can display a stock chart in just 1 line:

var aapl = new StockData(new StockID("AAPL", "NASDAQ"), new MarketArchiveHttpReader());
new TimeSeriesChart().add(aapl)

Technical Analysis with TA4J

Ta4j is an open source Java library for technical analysis. It provides the basic components for creation, evaluation and execution of trading strategies.

We can use our StockData functionality as data source for TA4J to e.g. to calculate indicators:

var stockData:IStockData = new StockData(new StockID("AAPL", "NASDAQ"), new MarketArchiveHttpReader());
// translate to Ta4j TimeSeries
var series = new Ta4jTimeSeries(stockData, new DateRange(Context.date("2017-01-01"),new Date()));
// Closing Prices
var closePrice:Indicator[Decimal] = new ClosePriceIndicator(series);
// Getting the simple moving average (SMA) of the close price over the last 5 ticks
var shortSma:Indicator[Decimal] = new SMAIndicator(closePrice, 5);
// Getting a longer SMA (e.g. over the 30 last ticks)
var longSma:Indicator[Decimal] = new SMAIndicator(closePrice, 30);

// create chart
var chart = new TimeSeriesChart()
chart.add(shortSma,"shortSma")
chart.add(closePrice,"close")
chart.add(longSma,"longSma")

chart

Trading with TA4J

Here is the complete trading and evaluation example which we took from the TA4J documentation that can be found at
https://github.com/ta4j/ta4j/wiki/Getting%20started.

The example has been converted to Scala:

var stockData = new StockData(new StockID("AAPL", "NASDAQ"), new MarketArchiveHttpReader());
var series = new Ta4jTimeSeries(stockData);
var closePrice = new ClosePriceIndicator(series);

// Getting the simple moving average (SMA) of the close price over the last 5 ticks
var shortSma = new SMAIndicator(closePrice, 5);
// Getting a longer SMA (e.g. over the 30 last ticks)
var longSma = new SMAIndicator(closePrice, 30);

// Buying rules
// We want to buy:
//  - if the 5-ticks SMA crosses over 30-ticks SMA
//  - or if the price goes below a defined price (e.g $800.00)
var buyingRule = new CrossedUpIndicatorRule(shortSma, longSma)
        .or(new CrossedDownIndicatorRule(closePrice, Decimal.valueOf("800")));

// Selling rules
// We want to sell:
//  - if the 5-ticks SMA crosses under 30-ticks SMA
//  - or if if the price looses more than 3%
//  - or if the price earns more than 2%
var sellingRule = new CrossedDownIndicatorRule(shortSma, longSma)
        .or(new StopLossRule(closePrice, Decimal.valueOf("3")))
        .or(new StopGainRule(closePrice, Decimal.valueOf("2")));

var strategy = new BaseStrategy(buyingRule, sellingRule);

// Running our juicy trading strategy...
var manager = new TimeSeriesManager(series);
var tradingRecord = manager.run(strategy);
println("Number of trades for our strategy: " + tradingRecord.getTradeCount());

// Getting the cash flow of the resulting trades
var cashFlow = new CashFlow(series, tradingRecord);

// Getting the profitable trades ratio
var profitTradesRatio = new AverageProfitableTradesCriterion();
println("Profitable trades ratio: " + profitTradesRatio.calculate(series, tradingRecord));

// Getting the reward-risk ratio
var rewardRiskRatio = new RewardRiskRatioCriterion();
println("Reward-risk ratio: " + rewardRiskRatio.calculate(series, tradingRecord));

// Total profit of our strategy
// vs total profit of a buy-and-hold strategy
var vsBuyAndHold = new VersusBuyAndHoldCriterion(new TotalProfitCriterion());
println("Our profit vs buy-and-hold profit: " + vsBuyAndHold.calculate(series, tradingRecord));

"--END--"

Number of trades for our strategy: 218
Profitable trades ratio: 0.536697247706422
Reward-risk ratio: 1.8774625448568232
Our profit vs buy-and-hold profit: 0.0019066141135999938





--END--

So far we have seen how we can use our functionality toghether with TA4J to implement an automatic trading and evaluation platform.

In the next Chapter we demonstrate our own Trading Simulation and Optimization functionality.

Accounts and Paper Trader

The Account class is used to record and evaluate trades. We need to indicate the opening amount, the open date of the account and the Fees Model (IFeesModel).
We can optionally register a generic reader or a ticker specific reader which defines from where the stock information is read.

The requested stock trades are recorded with the addTransaction() method. Positive quantities are purchased, negative quantities are sold.

The paper trader implements the basic trading (simulation) functionality. We can indicate a delay (with setDelay() and the price logic with setPrice(). In our example the trade is executed on the next day with the open rate.

With the execute() method we start the processing which is processing the open unfilled orders.

var stockdata = new StockID("AAPL", "NASDAQ");
var account = new Account("Simulation","USD", 100000.00, Context.date("2015-01-01"), new PerTradeFees(10.0));

account.putReader(new MarketArchiveHttpReader());
account.addTransaction(new Transaction(Context.date("2015-01-04"), stockdata, +100l));
account.addTransaction(new Transaction(Context.date("2015-10-04"), stockdata, -90l));

var trader = new PaperTrader(account);
// configure alternative logic
trader.setDelay(new OneDayDelay());
trader.setPrice(new OpenPrice());
trader.execute();

// display the resulting transactions
Displayers.display(account.getTransactions());

active	stockID	date	quantity	requestedPrice	filledPrice	fees	comment	id	impactOnCash	buyOrSell	requestedPriceType
true	Key Value ticker Cash exchange Account	2015-01-01	0	0	0	0		7217808a-02f5-4204-8c33-0ffb74e1e423	100000	NA	CashTransfer
true	Key Value ticker AAPL exchange NASDAQ	2015-01-05	100	0	102.5099	10		d8590f3b-7f8c-4795-8eaa-a01e73ce0f91	-10260.9933	Buy	Market
true	Key Value ticker AAPL exchange NASDAQ	2015-10-05	-90	0	105.3364	10		fd1bd3ec-b5fb-4a86-8521-84e9c20d9d2a	9470.2776	Sell	Market

Trading Strategies

The heart of automatic trading are the “trading strategies”. A class which implements ITradingStrategy can be used for automatic trading. A class which implements IOptimizableTradingStrategy can be used for automatic parameter optimization and automatic trading.

The framework comes with the following standard strategies:

TradingStrategyFactory.list()

[CCICorrectionStrategy, GlobalExtremaStrategy, MovingMomentumStrategy, RSI2Strategy, BuyAndHoldStrategy]

The Fitness class will be used to evaluate the strategies. As a result it provides both the input and the calculated KPI ouput parameters and updates the account.

You can use the SimulatedFitness class if you want to avoid the update to the account.

Displayers.display(account.getTransactions().collect(Collectors.toList()))

active	stockID	date	quantity	requestedPrice	filledPrice	fees	comment	id	impactOnCash	buyOrSell	requestedPriceType
true	Key Value ticker Cash exchange Account	2015-01-01	0	0	0	0		7217808a-02f5-4204-8c33-0ffb74e1e423	100000	NA	CashTransfer
true	Key Value ticker AAPL exchange NASDAQ	2015-01-05	100	0	102.5099	10		d8590f3b-7f8c-4795-8eaa-a01e73ce0f91	-10260.9933	Buy	Market
true	Key Value ticker AAPL exchange NASDAQ	2015-10-05	-90	0	105.3364	10		fd1bd3ec-b5fb-4a86-8521-84e9c20d9d2a	9470.2776	Sell	Market

var account = new Account("Simulation","USD", 100000.00, Context.date("2015-01-01"), new PerTradeFees(10.0));
var stockdata = new StockData(new StockID("AAPL", "NASDAQ"), new MarketArchiveHttpReader());
var strategy = new RSI2Strategy(stockdata);
var trader = new PaperTrader(account);
var state = new Fitness(trader).getFitness(strategy, account.getDateRange());

// print one parameter
println("Return: " + state.result().getValue(KPI.AbsoluteReturn));

// print all parameters
Displayers.display(state.result().getParameters())

Return: 56741.0

Key	Value
ReturnPercentAnualized	19
NumberOfTrades	5
SharpeRatio	1
MaxDrawDownPercent	33517
PurchasedValue	92884
ReturnPurcentStdDev	0
RealizedGains	-7066
NumberOfBuys	3
TotalFees	50
AbsoluteReturn	56741
MaxDrawDownLowValue	88757
MaxDrawDownNumberOfDays	458
AbsoluteReturnAvaragePerDay	74
ActualValue	156741
MaxDrawDownHighValue	122274
AbsoluteReturnStdDev	1235
UnrealizedGains	63858
ReturnPercent	57
NumberOfTradedStocks	1
Cash	97
NumberOfCashTransfers	1
NumberOfSells	2

Displayers.display(account.getTransactions())

active	stockID	date	quantity	requestedPrice	filledPrice	fees	comment	id	impactOnCash	buyOrSell	requestedPriceType
true	Key Value ticker Cash exchange Account	2015-01-01	0	0	0	0		1af70412-cea9-4c63-a3ad-5e6ba047f31b	100000	NA	CashTransfer
true	Key Value ticker AAPL exchange NASDAQ	2015-01-12	966	0	103.4187	10		1e16cf8a-81fb-4115-8bff-6e65abc38749	-99912.458	Buy	Market
true	Key Value ticker AAPL exchange NASDAQ	2015-08-17	-966	0	112.3154	10		5bf75205-f175-4760-9ec9-6a8402bd5219	108486.6756	Sell	Market
true	Key Value ticker AAPL exchange NASDAQ	2016-04-15	1020	0	106.3323	10		c4543d5d-108e-4383-8088-d723dab52bfd	-108468.9442	Buy	Market
true	Key Value ticker AAPL exchange NASDAQ	2016-05-10	-1020	0	90.979	10		3fbc5afb-00f2-49ca-bce4-364a77cbe0b1	92788.5762	Sell	Market
true	Key Value ticker AAPL exchange NASDAQ	2016-08-11	878	0	105.6793	10		58710958-a9ac-49eb-861f-9ec8b66d5988	-92796.3972	Buy	Market

// create chart for total values
var chart = new TimeSeriesChart();
chart.add(account.getTotalValueHistory(), "Total Value")
chart.add(account.getCashHistoryForAllDates(), "Cash")
chart.add(account.getActualValueHistory(), "Actual Value")
chart.addLabels(account.getTransactions())

chart

In order to get a better understanding of the development of the values over time we can
chart the Acocunt information.

Displayers.display(account.getTransactions())

active	stockID	date	quantity	requestedPrice	filledPrice	fees	comment	id	impactOnCash	buyOrSell	requestedPriceType
true	Key Value ticker Cash exchange Account	2015-01-01	0	0	0	0		1af70412-cea9-4c63-a3ad-5e6ba047f31b	100000	NA	CashTransfer
true	Key Value ticker AAPL exchange NASDAQ	2015-01-12	966	0	103.4187	10		1e16cf8a-81fb-4115-8bff-6e65abc38749	-99912.458	Buy	Market
true	Key Value ticker AAPL exchange NASDAQ	2015-08-17	-966	0	112.3154	10		5bf75205-f175-4760-9ec9-6a8402bd5219	108486.6756	Sell	Market
true	Key Value ticker AAPL exchange NASDAQ	2016-04-15	1020	0	106.3323	10		c4543d5d-108e-4383-8088-d723dab52bfd	-108468.9442	Buy	Market
true	Key Value ticker AAPL exchange NASDAQ	2016-05-10	-1020	0	90.979	10		3fbc5afb-00f2-49ca-bce4-364a77cbe0b1	92788.5762	Sell	Market
true	Key Value ticker AAPL exchange NASDAQ	2016-08-11	878	0	105.6793	10		58710958-a9ac-49eb-861f-9ec8b66d5988	-92796.3972	Buy	Market

Trading Strategies Description

import scala.collection.JavaConversions._

var list = new ArrayList[HashMap[String,String]]()
for (strategy <-  TradingStrategyFactory.list()) {
    var map = new HashMap[String,String]();
    map.put("Name", strategy)
    map.put("Description",TradingStrategyFactory.getStrategyDesciption(strategy))
    list.add(map)
}

Displayers.display(list)

Description	Name
Developed by Donald Lambert, the Commodity Channel Index (CCI) is a momentum oscillator that can be used to identify a new trend or warn of extreme conditions. This strategy uses weekly CCI to dictate the trading bias when it surges above +100 or plunges below -100, which are key levels noted by Lambert. Once the trading bias is set, daily CCI is used to generate trading signals when it reaches its extremes.Details can be found in stockcharts	CCICorrectionStrategy
This strategy compares the current price to the global extrema over a week. We ar going long if the close price goes below the minimum price. We are going short if the close price goes above the maximum price.	GlobalExtremaStrategy
Many trading strategies are based on a process, not a single signal. This process often involves a series of steps that ultimately lead to a signal. Typically, chartists first establish a trading bias or long-term perspective. Second, chartists wait for pullbacks or bounces that will improve the risk-reward ratio. Third, chartists look for a reversal that indicates a subsequent upturn or downturn in price. The strategy put forth here uses moving average to define the trend, the Stochastic Oscillator to identify corrections within that trend and the MACD-Histogram to signal short-term reversals. It is a complete strategy based on a three step process. http://stockcharts.com/school/doku.php?id=chart_school:trading_strategies:moving_momentum	MovingMomentumStrategy
Developed by Larry Connors, the 2-period RSI strategy is a mean-reversion trading strategy designed to buy or sell securities after a corrective period. The strategy is rather simple. Connors suggests looking for buying opportunities when 2-period RSI moves below 10, which is considered deeply oversold. Conversely, traders can look for short-selling opportunities when 2-period RSI moves above 90. This is a rather aggressive short-term strategy designed to participate in an ongoing trend. It is not designed to identify major tops or bottoms. Before looking at the details, note that this article is designed to educate chartists on possible strategies. We are not presenting a stand-alone trading strategy that can be used right out of the box. Instead, this article is meant to enhance strategy development and refinement. See http://stockcharts.com/school/doku.php?id=chart_school:trading_strategies:rsi2.	RSI2Strategy
We buy the title when the account is opened and hold the stock. This strategy can be used as a baseline to compare the other strategies.	BuyAndHoldStrategy

Comparing Trading Strategies

Here is a small example which compares the trading strategies for Apple starting from 2015-01-01

import java.util.ArrayList

def calculateResult(account:Account, strategy : IOptimizableTradingStrategy) : java.util.Map[String,Object] = {
    var state = new SimulatedFitness(account).getFitness(strategy, account.getDateRange());
    var result = state.getMap();
    // add strategy name to result
    result.put("Strategy", strategy.getClass().getSimpleName());
    return result;
}

var account = new Account("Simulation","USD", 100000.00, Context.date("2015-01-01"), new PerTradeFees(10.0));
var sd = Context.getStockData("AAPL", "NASDAQ");

var result = new ArrayList[java.util.Map[String,Object]]();
result.add(calculateResult(account, new RSI2Strategy(sd)));
result.add(calculateResult(account, new BuyAndHoldStrategy(sd)));
result.add(calculateResult(account, new CCICorrectionStrategy(sd)));
result.add(calculateResult(account, new GlobalExtremaStrategy(sd)));
result.add(calculateResult(account, new MovingMomentumStrategy(sd)));

Displayers.display(result)

PurchasedValue	SharpeRatio	RealizedGains	UnrealizedGains	LongSMAPeriod	Cash	MaxDrawDownLowValue	NumberOfTrades	NumberOfTradedStocks	EntryLimit	RSIPeriod	NumberOfCashTransfers	AbsoluteReturnAvaragePerDay	NumberOfSells	MaxDrawDownHighValue	ShortSMAPeriod	ReturnPercentAnualized	AbsoluteReturnStdDev	ExitLimit	AbsoluteReturn	NumberOfBuys	ReturnPercent	TotalFees	MaxDrawDownNumberOfDays	ActualValue	MaxDrawDownPercent	ReturnPurcentStdDev	Strategy
92884	1	-7066	63858	200	97	88757	5	1	5	2	1	74	2	122274	5	19	1235	95	56741	3	57	50	458	156741	33517	0	RSI2Strategy
99990	1	0	72368		14	85003	1	1			1	94	0	122201		24	1615		72358	1	72	10	426	172358	37198	0	BuyAndHoldStrategy
79404	1	-20566	48741		47	74745	3	1			1	37	1	102875		9	1106		28145	2	28	30	487	128145	28130	0	CCICorrectionStrategy
139839	1	40279	0		139839	94371	44	1			1	52	22	112952		13	1031		39839	22	40	440	318	139839	18582	0	GlobalExtremaStrategy
105885	0	5925	0		105885	83121	4	1			1	8	2	106331		2	740		5885	2	6	40	331	105885	23210	0	MovingMomentumStrategy

Custom Trading Strategies

Finally we demonstrate how you can implement your custom Strategy. The indicators and trading strategy functionality is based on TA4J https://github.com/ta4j/ta4j.

The simplest and fastest way is to implement a BaseStrategy by extending the CommonTradingStrategy:

import ch.pschatzmann.dates._;
import ch.pschatzmann.stocks._;
import ch.pschatzmann.stocks.accounting._;
import ch.pschatzmann.stocks.integration._;
import ch.pschatzmann.stocks.execution._;
import ch.pschatzmann.stocks.execution.fees._;
import ch.pschatzmann.stocks.strategy._;
import ch.pschatzmann.stocks.strategy.optimization._;
import ch.pschatzmann.stocks.input._;
import ch.pschatzmann.stocks.parameters._;
import org.ta4j.core._;
import org.ta4j.core.analysis._;
import org.ta4j.core.analysis.criteria._;
import org.ta4j.core.indicators._;
import org.ta4j.core.indicators.helpers._;
import org.ta4j.core.trading.rules._;
import ch.pschatzmann.display.Displayers

class DemoStrategy(sd : StockData) extends CommonTradingStrategy (sd){
    // Define BaseStrategy
    def buildStrategy(timeSeries : TimeSeries) : BaseStrategy = {
        val closePrices = new ClosePriceIndicator(timeSeries);
        // Getting the max price over the past week
        val maxPrices = new MaxPriceIndicator(timeSeries);
        val weekMaxPrice = new HighestValueIndicator(maxPrices, 7);
        // Getting the min price over the past week
        val minPrices = new MinPriceIndicator(timeSeries);
        val weekMinPrice = new LowestValueIndicator(minPrices, 7);
        // Going long if the close price goes below the min price
        val downWeek = new MultiplierIndicator(weekMinPrice, Decimal.valueOf(1.004));
        val buyingRule = new UnderIndicatorRule(closePrices, downWeek);
        // Going short if the close price goes above the max price
        val upWeek = new MultiplierIndicator(weekMaxPrice, Decimal.valueOf(0.996));
        val sellingRule = new OverIndicatorRule(closePrices, upWeek);

        return new BaseStrategy(buyingRule, sellingRule);
    }  
}

var apple = new StockData(new StockID("AAPL", "NASDAQ"), new MarketArchiveHttpReader());
var account = new Account("Simulation","USD", 100000.00, Context.date("2015-01-01"), new PerTradeFees(10.0));
var strategy = new DemoStrategy(apple);
var trader = new PaperTrader(account);
var state = new Fitness(trader).getFitness(strategy, account.getDateRange());

//println("Return: "+state.result().getValue(KPI.AbsoluteReturn));
Displayers.display(state.getMap());

Key	Value
AbsoluteReturnStdDev	1031
PurchasedValue	139839
SharpeRatio	1
RealizedGains	40279
AbsoluteReturn	39839
UnrealizedGains	0
NumberOfBuys	22
Cash	139839
ReturnPercent	40
MaxDrawDownLowValue	94371
TotalFees	440
MaxDrawDownNumberOfDays	318
NumberOfTrades	44
NumberOfTradedStocks	1
NumberOfCashTransfers	1
ActualValue	139839
MaxDrawDownPercent	18582
ReturnPurcentStdDev	0
AbsoluteReturnAvaragePerDay	52
NumberOfSells	22
MaxDrawDownHighValue	112952
ReturnPercentAnualized	13

An alternaive approach is to implement the interface directly:

import ch.pschatzmann.dates._;
import ch.pschatzmann.stocks._;
import ch.pschatzmann.stocks.accounting._;
import ch.pschatzmann.stocks.integration._;
import ch.pschatzmann.stocks.execution._;
import ch.pschatzmann.stocks.execution.fees._;
import ch.pschatzmann.stocks.strategy._;
import ch.pschatzmann.stocks.strategy.optimization._;
import ch.pschatzmann.stocks.input._;
import ch.pschatzmann.stocks.parameters._;
import org.ta4j.core._;
import org.ta4j.core.analysis._;
import org.ta4j.core.analysis.criteria._;
import org.ta4j.core.indicators._;
import org.ta4j.core.indicators.helpers._;
import org.ta4j.core.trading.rules._;
import ch.pschatzmann.display.Displayers

/**
 * Strategy implemented in Scala 
 */
class DemoStrategy extends ITradingStrategy {
    var state = new State();
    val stockdata = new StockData(new StockID("AAPL", "NASDAQ"), new MarketArchiveHttpReader());

    def getStrategy():Strategy = {
        var timeSeries = new Ta4jTimeSeries(getStockData());
        val closePrices = new ClosePriceIndicator(timeSeries);
        // Getting the max price over the past week
        val maxPrices = new MaxPriceIndicator(timeSeries);
        val weekMaxPrice = new HighestValueIndicator(maxPrices, 7);
        // Getting the min price over the past week
        val minPrices = new MinPriceIndicator(timeSeries);
        val weekMinPrice = new LowestValueIndicator(minPrices, 7);
        // Going long if the close price goes below the min price
        val downWeek = new MultiplierIndicator(weekMinPrice, Decimal.valueOf(1.004));
        val buyingRule = new UnderIndicatorRule(closePrices, downWeek);
        // Going short if the close price goes above the max price
        val upWeek = new MultiplierIndicator(weekMaxPrice, Decimal.valueOf(0.996));
        val sellingRule = new OverIndicatorRule(closePrices, upWeek);

        return new BaseStrategy(buyingRule, sellingRule);
    }

    def getStockData():StockData = {
        return stockdata;
    }

    def getName():String = {
        return "DemoStrategy";
    }

    def getDescription():String = {
        return "Demo strategy implemented in scala";
    }

    def getParameters():State = {
        return state;
    }

    def reset() {}

}

var account = new Account("Simulation","USD", 100000.00, Context.date("2015-01-01"), new PerTradeFees(10.0));
var strategy = new DemoStrategy();
var trader = new PaperTrader(account);
var state = new Fitness(trader).getFitness(strategy,account.getDateRange());

//println("Return: "+state.result().getValue(KPI.AbsoluteReturn));
Displayers.display(state.getMap());

Key	Value
AbsoluteReturnStdDev	1031
PurchasedValue	139839
SharpeRatio	1
RealizedGains	40279
AbsoluteReturn	39839
UnrealizedGains	0
NumberOfBuys	22
Cash	139839
ReturnPercent	40
MaxDrawDownLowValue	94371
TotalFees	440
MaxDrawDownNumberOfDays	318
NumberOfTrades	44
NumberOfTradedStocks	1
NumberOfCashTransfers	1
ActualValue	139839
MaxDrawDownPercent	18582
ReturnPurcentStdDev	0
AbsoluteReturnAvaragePerDay	52
NumberOfSells	22
MaxDrawDownHighValue	112952
ReturnPercentAnualized	13

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