Mechanical Bird Song Device from 1890

High-Speed Robot Hand

Unit Testing Runtime Exceptions with JUnit4 and Hamcrest

Junit and Hamcrest make unit testing with Java almost enjoyable. In this post, I show how to unit test Exceptions with JUnit4 and Hamcrest. In this over-simplified example, I'm testing a method that always throws an IllegalArgumentException. In real-life the IllegalArgumentException would only be thrown under special circumstances given certain arguments, and those are the ones you want to test with the unit test.

The basic idea is to surround the method you want to test with a try catch block and pass it an argument that will trigger the IllegalArgumentException to be thrown. The fail method call should never be reached, and if it does the unit test should fail. What should happen is that the IllegalArgumentException is caught, followed by a check for the correct message.

import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.junit.Assert.fail;

import org.junit.Test;

/**
 * The following example code demonstrates how to unit test Exceptions with JUnit and Hamcrest
 */
public class ExceptionUnitTesting {

  @Test
  public void test() {

    try {
      blah("asdf");
      fail("Expected exception");
    } catch (IllegalArgumentException e) {
      assertThat(e.getMessage(), is(equalTo("Argument foo is not valid!")));
    }
  }

  /**
   * @param foo
   * @throws IllegalArgumentException - in this test case always
   */
  private void blah(String foo) {

    throw new IllegalArgumentException("Argument foo is not valid!");
  }
}

Piece of Cake!!!

Import a Maven Git Project Into Eclipse

The Easy Way

Prerequisites
Install M2Eclipse

Step 1: Clone or create Git Repo. First, you need to clone a Git repo into an empty folder in your workspace. You need to use a Git client such as SourceTree or TortoiseGit for this. Create you workspace first if it isn't already, and clone the git repo directly into a new folder labeled with the project name.

Step 2: Import Into Eclipse. In the Package Explorer view, right-click and choose Import... In the wizard choose Maven -> "Existing Maven Projects" as the project type. Search for the project home directory and click though the wizard.

The Hard Way

Prerequisites
Install M2Eclipse
Install egit

Step 1: Right-click in the Package Explorer area and select Import..., select Maven -> Check out Maven Projects from SCM, and click Next.

Step 2: Choose "git" as the SCM connector next to "SCM URL:" and type in the Git repo URL. If there are no connectors to choose from you have to first install that Eclipse plugin. To do that, click on the "m2e Marketplace" link in the lower right hand corner of the dialog box.

Step 3: Check m2e-egit and click Finish.

Step 4: Select "git" as the SCM connector and type in the Git repo URL.

Step 5: After asking you for the passphrase for ssh access to the Git repo, it will download and import the Java project as a Maven project into your workspace.

Piece of Cake!!!

Bird Brains

Bacteria as a Superorganism

Good Overview of Superstring Theory

What Is Life Really?

Avoiding Name Collisions When Organizing Imports in Eclipse

Is there any way to get Eclipse to automatically give preference to a preferred import when organizing imports? Thankfully, the answer is yes.

For example, I'd like to be able to write:

List myList = new ArrayList();

hit Ctrl + Shift + O and have Eclipse add:

import java.util.List;

And not always ask me which List I want to import:

To tell Eclipse not to ever consider java.awt.List, for example, go to Preferences --> Java --> Appearance --> Type Filters menu. Click add and enter Types you do not want Eclipse to consider for automatic insertion of import statements.

Piece of Cake!!!

XChange - Open Source Java API for MtGox Bitcoin Exchange

UPDATE March 9, 2013: Version 1.5.0 released. Support for 10 exchanges.

UPDATE Jan 31, 2013: Version 1.4.0 released. Support for Canadian Virtual Exchange. Mostly bug fixes.

UPDATE Jan 16, 2013: Version 1.3.0 released. Support for many more exchanges. See release notes and also XChange Release 1.3.0 Announcement

UPDATE Oct 11, 2012: Version 1.2.0 released. Support for Canadian Virtual Exchange.

Supported Exchanges

Together with other members from the Bitcoin community, I've recently created a new open source Java library called XChange. XChange is a Java library providing a simple and consistent API for interacting with a diverse set of financial security exchanges including Bitcoin. The first exchange implemented is the world's largest Bitcoin exchange - Mt Gox. The plan is to add more Bitcoin exchanges and other traditional financial exchanges offerring trading APIs such as Interactive Brokers.

As of the most recent release 1.1.0, Xchange offers the following functionality:

• Support for MtGox Bitcoin Exchange (public) polling market data (ticker, depth, trades, etc.)
• Support for MtGox Bitcoin Exchange (private) polling trade data (account info, market order, limit order, cancel order open orders, etc.)
• Support for MtGox Bitcoin Exchange (public) streaming market (ticker)

Next up on the todo list is:

• Support for MtGox Bitcoin Exchange (public) streaming market (depth, trades, etc.)
• Support for MtGox Bitcoin Exchange (private) streaming trade data (account info, market order, limit order, cancel order open orders, etc.)

Relevant Links

Project Home - http://xeiam.com/xchange.jsp
Code on Github - https://github.com/timmolter/XChange
Example Code - http://xeiam.com/xchange_examplecode.jsp

Examples

The following examples demonstrate getting Ticker data from MtGox, first using the polling API, and second using the streaming API.

Ticker via Polling API

package com.xeiam.xchange.examples.mtgox.v1.polling;

import com.xeiam.xchange.Currencies;
import com.xeiam.xchange.Exchange;
import com.xeiam.xchange.ExchangeFactory;
import com.xeiam.xchange.dto.marketdata.Ticker;
import com.xeiam.xchange.service.marketdata.polling.PollingMarketDataService;

/**
 * Test requesting polling Ticker at MtGox
 */
public class TickerDemo {

  private static PollingMarketDataService marketDataService;

  public static void main(String[] args) {

    // Use the factory to get the version 1 MtGox exchange API using default settings
    Exchange mtGox = ExchangeFactory.INSTANCE.createExchange("com.xeiam.xchange.mtgox.v1.MtGoxExchange");

    // Interested in the public polling market data feed (no authentication)
    marketDataService = mtGox.getPollingMarketDataService();

    // Get the latest ticker data showing BTC to USD
    Ticker ticker = marketDataService.getTicker(Currencies.BTC, Currencies.USD);
    double value = ticker.getLast().getAmount().doubleValue();
    String currency = ticker.getLast().getCurrencyUnit().toString();
    System.out.println("Last: " + currency + "-" + value);

    System.out.println("Last: " + ticker.getLast().toString());
    System.out.println("Bid: " + ticker.getBid().toString());
    System.out.println("Ask: " + ticker.getAsk().toString());

    // Get the latest ticker data showing BTC to EUR
    ticker = marketDataService.getTicker(Currencies.BTC, Currencies.EUR);
    System.out.println("Last: " + ticker.getLast().toString());
    System.out.println("Bid: " + ticker.getBid().toString());
    System.out.println("Ask: " + ticker.getAsk().toString());

    // Get the latest ticker data showing BTC to GBP
    ticker = marketDataService.getTicker(Currencies.BTC, Currencies.GBP);
    System.out.println("Last: " + ticker.getLast().toString());
    System.out.println("Bid: " + ticker.getBid().toString());
    System.out.println("Ask: " + ticker.getAsk().toString());

  }

}

Result:

Last: USD-5.14739
Last: USD 5.14739
Bid: USD 5.12011
Ask: USD 5.1299

Last: EUR 4.07
Bid: EUR 4.0527
Ask: EUR 4.07

Last: GBP 3.3452
Bid: GBP 3.3
Ask: GBP 3.34091

Ticker via Streaming API

package com.xeiam.xchange.examples.mtgox.v1.streaming;

import java.util.concurrent.BlockingQueue;

import com.xeiam.xchange.Currencies;
import com.xeiam.xchange.Exchange;
import com.xeiam.xchange.dto.marketdata.Ticker;
import com.xeiam.xchange.mtgox.v1.MtGoxExchange;
import com.xeiam.xchange.service.marketdata.streaming.StreamingMarketDataService;

/**
 * Test requesting streaming Ticker at MtGox
 */
public class TickerDemo {

  public static void main(String[] args) {

    TickerDemo tickerDemo = new TickerDemo();
    tickerDemo.start();
  }

  private void start() {

    // Use the default MtGox settings
    Exchange mtGox = MtGoxExchange.newInstance();

    // Interested in the public streaming market data feed (no authentication)
    StreamingMarketDataService streamingMarketDataService = mtGox.getStreamingMarketDataService();

    // Get blocking queue that receives streaming ticker data
    BlockingQueue tickerQueue = streamingMarketDataService.requestTicker(Currencies.BTC, Currencies.USD);

    // take streaming ticker data from the queue and do something with it
    while (true) {
      try {
        // Put your ticker event handling code here
        doSomething(tickerQueue.take());
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }
  }

  /**
   * Do something fun with the streaming data!
   * 
   * @param ticker
   */
  private void doSomething(Ticker ticker) {

    System.out.println(ticker.toString());
  }

}

Result:

Ticker [timestamp=2012-08-26T20:09:13.202Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3078691906206]
Ticker [timestamp=2012-08-26T20:09:18.651Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:19.568Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:23.152Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:23.975Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:24.790Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:25.205Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:26.018Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]
Ticker [timestamp=2012-08-26T20:09:26.543Z, last=USD 10.6, bid=USD 10.55248, ask=USD 10.6, tradableIdentifier=BTC, volume=3068691906206]

Piece of Cake!!!