I was working on my Android app skills and was creating a simple calculator. It was very basic and worked great until I started to play with division. I thought, this will be easy. Just type, 3 / 2 = and I would be given the answer. We all know the answer is, of course, 1.49999998.

Wait a minute! Why would this be the answer you ask? This has to do with the data type used and if you are doing calculations where the result really matters such as for money, then you should not be using a double or a float type.

BigDecimal to the rescue. The BigDecimal type “fixes” the issues that come up when you are using decimal numbers and stop the precision loss. This means that the 3 / 2 = will indeed give you 1.5. But you need to use the BigDecimal functions to add, subtract, multiply and divide. Not just the ‘+’ (plus), ‘-‘ (minus), ‘*’ (multiply), ‘/’ (divide) operators.

Instead of using doubles, like this:

double firstNumber = 3;
double secondNumber = 2;

You should use BigDecimal, like this:

BigDecimal firstNumber = new BigDecimal(3);
BigDecimal secondNumber = new BigDecimal(2);

But now when you try to add, subtract, multiply or divide using a the traditional operators, it no longer works. You will need to replace them with the methods named after the operations you are attempting.

// Add 
double addResult = firstNumber + secondNumber;  //error
BigDecimal addResultBd = firstNumber.add(secondNumber);
// Subtract 
double subtractResult = firstNumber - secondNumber; //error
BigDecimal subtractResultBd = firstNumber.subtract(secondNumber);
// Multiply
double multiplyResult = firstNumber * secondNumber; //error
BigDecimal multiplyResultBd = firstNumber.multiply(secondNumber);
// Divide
double divideResult = firstNumber / secondNumber; //error
BigDecimal divideResultBd = firstNumber.divide(secondNumber);

So using BigDecimal can save your sanity when your calculations are critical to what you are expecting. Calculators that give you a “close enough” representation of the numbers you are expecting are not very good.

I have been enjoying learning Hadoop and have had to debug issues within a current process job to enhance it for new data points. It is quite the challenge to debug a distributed system but I have found two ways to get some meaningful input from the system. One way is using Counters and the other is to use MultipleOutputs to capture output from errors(This will be in a later post). This article will show how counters can be used.

The Counter method allows you to specify a set of enum values to specify the counter name:

public enum Counters {
  CHOCOLATE,
  VANILLA,
  MINT_CHOCO_CHIP
}

This will be used as the identifier for the counter that is in use. The same code can be used within the Mapper or the reducer depending on where you are looking for the counts. The difference is where in the final output of the Hadoop process that the counts show up.

if (flavor.contains("CHOCOLATE")) {
    context.getCounter(Counters.CHOCOLATE).increment(1);
}
if (flavor.contains("VANILLA")) {
    context.getCounter(Counters.VANILLA).increment(1);
}
if (flavor.contains("MINT_CHOCO_CHIP")) {
    context.getCounter(Counters.MINT_CHOCO_CHIP).increment(1);
}

This way you will find a line for each counter that was incremented during the Hadoop process.

I have used it to highlight problems with in the code or just to make sure that a segment of code has been run.

Tags: BigData, hadoop

I was updating some plugins for a project and came to a query for an e-mail program I was writing, I had to send out recently introduced defects to their respective owners and insure that they would only get the defects from the a given offset. It turned out that my API had a XMLGregorianCalendar argument. So I went out to look for a way to offset the date object so I could retrieve the correct information.

I used the following to convert my date:

package com.etechtips;

import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.XMLGregorianCalendar;

public class UpdateDate {

	public static void main(String[] args) {
		XMLGregorianCalendar xgcstart;
		GregorianCalendar gc;
		int daycount = 0;
		if (args.length != 1)
		{
			System.out.println("Need to specify offset");
			System.exit(1);
		}
		
		daycount = Integer.parseInt(args[0]);
		
		// This will get the current date based on System time of an object
		gc = new GregorianCalendar();
		System.out.println("CURRENT:" + gc.toString());

		// This will offset the date by daycount days
		gc.add(Calendar.DATE, daycount);
		System.out.println("OFFSET: "+ gc.toString());
		
		try
		{
			// Now the XMLGregorianCalendar object has an 
                        instance that is based on the time set in the gc object
			xgcstart = DatatypeFactory.newInstance().newXMLGregorianCalendar(gc);
		}
		catch(DatatypeConfigurationException dce)
		{
			dce.printStackTrace();
			System.exit(1);
		}
		
		// Code omitted 	
	}
}

Output:

CURRENT:java.util.GregorianCalendar[time=1321793315934,areFieldsSet=true,areAllFieldsSet=true,
lenient=true,zone=sun.util.calendar.ZoneInfo[id="America/Chicago",offset=-21600000,
dstSavings=3600000,useDaylight=true,transitions=235,
lastRule=java.util.SimpleTimeZone[id=America/Chicago,offset=-21600000,dstSavings=3600000,
useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,
startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,
endTimeMode=0]],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2011,MONTH=10,
WEEK_OF_YEAR=48,WEEK_OF_MONTH=4,DAY_OF_MONTH=20,DAY_OF_YEAR=324,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=3,
AM_PM=0,HOUR=6,HOUR_OF_DAY=6,MINUTE=48,SECOND=35,MILLISECOND=934,ZONE_OFFSET=-21600000,
DST_OFFSET=0]
OFFSET: java.util.GregorianCalendar[time=1321706915934,areFieldsSet=true,areAllFieldsSet=true,
lenient=true,zone=sun.util.calendar.ZoneInfo[id="America/Chicago",offset=-21600000,
dstSavings=3600000,useDaylight=true,transitions=235,lastRule=java.util.SimpleTimeZone[id=America/Chicago,
offset=-21600000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,
startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,
endDayOfWeek=1,endTime=7200000,endTimeMode=0]],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,
YEAR=2011,MONTH=10,WEEK_OF_YEAR=47,WEEK_OF_MONTH=3,DAY_OF_MONTH=19,DAY_OF_YEAR=323,
DAY_OF_WEEK=7,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=6,HOUR_OF_DAY=6,MINUTE=48,SECOND=35,
MILLISECOND=934,ZONE_OFFSET=-21600000,DST_OFFSET=0]

The printouts above show the current date and the new date based on the offset. I made the day of the month bold in the printouts to show what the offset has updated the date. You could put a much larger offset than 1 and Calendar object will take care of updating the day of week, week of year and more. You will not need to deal with checking for leap year or dealing with updating all the month and years, this is all taken care of for you.

Tags: Java, Programming

In each language that I have learned I have found it useful to know how to process command line arguments and here is a simple framework that I use for Java. I usually wrap the java command line in a bat or shell file to make it easier to run so that the user does not have to worry about classpath or path issues.

The following is the basic code to handle the command line arguments.

class CmdArgs
{

  public static void main(String[] args)
  {
      int argsize = args.length;
      String curarg;

      if (argsize > 0 )
      {
       
      }
      
      for(int i = 0; i < argsize; i++)
      {
          if (args[i].equals("--host"))
          {
             i++;
             host = args[i];
           }
          else if (args[i].equals("--debug"))
          {
               debug = 1;
          }
          else
          {
              System.out.println("Unknown option: " + args[i]);
              System.exit(1);
          }
       }

   }
}

The bat file for Dos/Windows might look like this:

@echo off

java -cp c:javabin;somejar.jar  com.etechtips.CmdArgs %*

The shell based file might look like:

java -cp /home/ecdown/javabin:somejar.jar com.etechtips.CmdArgs $*

Tags: Java, Scripts

Here is a list of the Hello World Programs for different languages:

C

#include <stdio.h>
int main()
{
printf("Hello World!");
}

C++

#include <iostream.h>
int main()
{
cout << "Hello World!" << endl;
}

C#

public class HelloWorld
  public static void Main()
  {
    System.Console.WriteLine("Hello World!");
  }

Java

class HelloWorld {
static void main(String[] args)
{
System.out.println("Hello World!");
}

SHELL

echo "Hello World"

Python 2

print "Hello World!\n"

Python 3

print ("Hello World!")

Ruby

puts "Hello World!"

Perl

print "Hello World!n";

PHP

  <?php      
    print "Hello World!";
  ?>

Rust

fn main() {
    println("Hello World!");
}

This is the simplest form of Hello World for most of these languages.

Tags: C, Java, perl, PHP, Programming, Python, Ruby, Shell

When attempting to run ant I get the following message: “Unable to locate tools.jar. Expected to find it in C:Program Files (x86)Javajre6libtools.jar”

This had to do with my JAVA_HOME not pointing to a Java JDK.

So if you download a JDK and update your JAVA_HOME environment variable to point to that directory, ant should run happily.

In BASH:
export JAVA_HOME=/path/to/jdk

IN DOS:
set JAVA_HOME=c:PATHtojdk

Tags: ant, Java

I had recently reinstalled my system and was trying to run a simple class that consisted
of a “Hello World” program in Java. I received the following:

Compile:

$> javac LottoMain.java

Run:

$> java LottoMain

Exception in thread “main” java.lang.NoClassDefFoundError: LottoMain
Caused by: java.lang.ClassNotFoundException: LottoMain
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:319)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:264)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:332)
Could not find the main class: LottoMain. Program will exit.

The compile line completed without errrors and the LottoMain.class file was there, but
what I didn’t know was that I no longer had the current directory “.” in my CLASSPATH variable.

After adding “.” to my CLASSPATH variable the run command gave me what I was expecting.

Run:

$> java LottoMain

Hello Eric!

Updating the CLASSPATH variable in Bash:
in my home directory/.bashrc file

export CLASSPATH=$CLASSPATH:.

Tags: Java, Programming

Starting on my road to creating a Java based GUI I stumbled upon the following link within the “Creating a GUI with JFC/Swing” Train in the Java Tutorials from Oracle.

Using Swing Components: Examples

It has code examples and can really get you started on the road to a Java GUI interface.

Tags: GUI, Java, Swing

This is the First of some basic articles about creating a GUI in Java. The following code is the basis of the following series of articles. I am using the Java Swing window toolkit.

import java.awt.*;
import java.swing.*;

class FirstWindow 
{

  public static void main(String[] args)
  {
      //Create Window object and set title bar text
      JFrame frame = new frame("First Window");

      // Set the Default operation when you close the window
      // This exits the program on closing the window
      // The default behavior is to HIDE_ON_CLOSE
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      // Now we need to Display the window
      // The null argument will place the element in the center of the screen.
      frame.setLocationRelativeTo(null);
      frame.pack();
      frame.setVisible(true);
   }
}

This is enough to display a simple window, but it will probably not have any useful size associated with it and it does not do anything.

The next step will be to add some useful widgets and eventually functionality to make the window useful.

Helpful info:
Java: Great link to Swing Examples

Tags: Java, Swing

If you are using maven to build your projects , then you might have found an out of memory condition in your tests.  Well, setting the MAVEN_OPTS variable with JVM specific options will help with this.

Example:

MAVEN_OPTS=-Xmx1024

Depending on what environment you are in, you will need to set this variable.

This will give the JVM more 1024 megs to work with and you can customize the number to fit your needs.