If you didn't get a chance to check out part I please read it first so this post makes a little more sense. My friend called me and said that he was done with his exercise and since it wasn't due for another 2 days he was going to try for extra credit. The extra credit was to have the program flow a little bit better and had to meet the following requirements.

• When the user clicks the cancel button the program must exit
• When the user enters something that doesn't meet our validation they must be prompted to re enter that data.

First off we need to solve this cancel button riddle. It happens to be a pretty simple answer. When you take input from the user and they click cancel, null is returned. So we can check for null and just exit the program. month = JOptionPane.showInputDialog(null,"Enter the month number from 1-12","Month",JOptionPane.QUESTION_MESSAGE); // if the user clicks cancel if( month == null){ System.exit(0); }

Now the next requirement is a little bit trickier. First off this program is impossible to write the way its currently constructed. If we ask for the day first there is no way for us to validate at that point if what they are entering is correct. Now if we ask for the month first then we can set our max days variable. So in this case to make it actually work I am going to ask for the month, day and then year. Now to accomplish this we have to use a while loop. What we to do is keep asking for the users input while a condition is true. In the case of our month we can do the following. What we are saying is while m is 0 (default setting) and greater than 12 (invalid month) keep asking for the input. while(m < 1 || m > 12){ month = JOptionPane.showInputDialog(null,"Enter the month number from 1-12","Month",JOptionPane.QUESTION_MESSAGE); // if the user clicks cancel if( month == null){ System.exit(0); } m = Integer.parseInt(month); }

Pretty simple but if you haven't worked with swing in awhile (this guy) it can be tricky. Here is the complete example. package com.vega.lab; import javax.swing.JOptionPane; public class DayMonthYearExtraCredit { static int m,d,y,maxDays = 0; static String day,month,year; static String monthName; static boolean isLeapYear; public static void main(String[] args) { // YEAR while(y == 0){ year = JOptionPane.showInputDialog(null,"Please enter the year, example 2009","Year",JOptionPane.QUESTION_MESSAGE); // if the user clicks cancel if( year == null){ System.exit(0); } try { y = Integer.parseInt(year); isLeapYear = (y % 4 == 0 && y % 100 != 0) || (y % 400 == 0); }catch(NumberFormatException nfe){ JOptionPane.showMessageDialog(null, "Please enter a valid number"); } } // MONTH while(m < 1 || m > 12){ month = JOptionPane.showInputDialog(null,"Enter the month number from 1-12","Month",JOptionPane.QUESTION_MESSAGE); // if the user clicks cancel if( month == null){ System.exit(0); } try { m = Integer.parseInt(month); switch(m){ case 1: monthName = "January"; maxDays = 31; break; case 2: monthName = "February"; if( isLeapYear ){ maxDays = 29; } else { maxDays = 28; } break; case 3: monthName = "March"; maxDays = 31; break; case 4: monthName = "April"; maxDays = 30; break; case 5: monthName = "May"; maxDays = 31; break; case 6: monthName = "June"; maxDays = 30; break; case 7: monthName = "July"; maxDays = 31; break; case 8: monthName = "August"; maxDays = 31; break; case 9: monthName = "September"; maxDays = 30; break; case 10: monthName = "October"; maxDays = 31; break; case 11: monthName = "November"; maxDays = 30; break; case 12: monthName = "December"; maxDays = 31; break; } }catch(NumberFormatException nfe){ JOptionPane.showMessageDialog(null, "Please enter a valid number"); } } // DAY while(d < 1 || d > maxDays ){ day = JOptionPane.showInputDialog(null,"Please enter the day, example 22","Day",JOptionPane.QUESTION_MESSAGE); // if the user clicks cancel if( day == null){ System.exit(0); } try { d = Integer.parseInt(day); }catch(NumberFormatException nfe){ JOptionPane.showMessageDialog(null, "Please enter a valid number"); } } // show the final result String out = monthName + " " + d + ", " + y; if( isLeapYear ){ out += " (Leap Year)"; } JOptionPane.showMessageDialog(null,out); } }

Update:

I just realized that our leap year requirement would not work the way I wrote it. The only way for this example to work correctly is to ask for the info in the exact opposite way the exercise wanted it. You need to know the year so that when you asking for the month you can set the correct number of max days and you need to know what the max days are when you are asking for the day.

This entry was posted on October 6, 2011 at 10:02 AM and has received 840 views. Comments 0 | Print this entry.

A friend of mine is taking some programming classes at a local community college and I asked him to forward me some of his exercises just for fun. I understand that these mini tests are supposed to teach you programming fundamentals but the veteran in me can't help but notice how unpractical they are and therefor tend to over think them.

Exercise

This week we are going to write a program that accepts a day, month and year. The program will then output the date in a readable format. So for example if the user enters 20,1,2011 the program will output January 20, 2011. Seems fairly simple but the requirements make it a little harder to take advantage of the Java API.

Requirements

• The user input needs to be implemented with Dialog boxes in a GUI fashion.
• There needs to be error checking on the input. For instance, the month number should be between 1 - 12, if not a user friendly error is submitted back to the user. Be sure to check the number of days in a month and the year for valid ranges.
• A switch statement needs to be implemented to convert the month number into the month name. Also, the switch logic should define the max allowable days in a month based on what month it is (e.g. January would have a max days of 31, whereas April would only have 30).
• The program needs to check if the day indicated is a leap day (i.e. Feb 29th, in a leap year). If so the user output needs to indicate that it is a leap year. The code for leap year calculations can be found in 3.13 on page 90. Please note: the input parameters of 29, 2, 2012 Needs to be at least one of your data sets, and shown in your output file as indicating a leap day ... within a leap year (Remeber this is two different checks).
• Finally, the output needs to be a GUI box back to the user indicating the text representation of the date, with indications of a leap day and leap year if found.

With those requirements here is what I came up. Now I realize that I am violating one of the rules here by not setting max number of days in the switch but that is what the API is for, to make my life easier. Maybe I would get extra credit :) package com.vega.labs; import java.util.Calendar; import java.util.GregorianCalendar; import javax.swing.JOptionPane; public class DayMonthYear { static int m,d,y,maxDays; static String day,month,year; static String monthName; static boolean isLeapYear; static String errors; public static void main(String[] args) { day = JOptionPane.showInputDialog(null,"Enter the day"); month = JOptionPane.showInputDialog(null,"Enter the month number"); year = JOptionPane.showInputDialog(null,"Enter the year number"); d = Integer.parseInt(day); m = Integer.parseInt(month); y = Integer.parseInt(year); Calendar cal = new GregorianCalendar(m,d,y); maxDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH); switch(m){ case 1: monthName = "January"; break; case 2: monthName = "February"; isLeapYear = (y % 4 == 0 && y % 100 != 0) || (y % 400 == 0); break; case 3: monthName = "March"; break; case 4: monthName = "April"; break; case 5: monthName = "May"; break; case 6: monthName = "June"; break; case 7: monthName = "July"; break; case 8: monthName = "August"; break; case 9: monthName = "September"; break; case 10: monthName = "October"; break; case 11: monthName = "November"; break; case 12: monthName = "December"; break; default : { // WRONG INPUT errors = "Please enter a month between 1-12\n"; break; } } if( d > maxDays ){ errors = "There are only " + maxDays + " days in " + monthName + " and you entered " + d + "\n"; } // If there are no errors show the final output if( errors == null ){ String out = monthName + " " + d + ", " + y; if( isLeapYear ){ out += " (Leap Year)"; } JOptionPane.showMessageDialog(null,out); } else { // let the user know what went wrong JOptionPane.showMessageDialog(null,errors); } } }

The only problem I have with it is there is no real logic way to trap for bad input. If a user enters a string an exception will be thrown. You could trap that exception but the way this excercise has been tossed up I am not sure it really would work. int m = 0; String in = JOptionPane.showInputDialog(null,"Enter the month number"); try { m = Integer.parseInt(in); }catch(NumberFormatException nx){ JOptionPane.showMessageDialog(null, "Enter a valid integer"); }

It has been a little while since I have written straight Java but this was fun! Would you change anything? I may ask my buddy to keep forwarding these over for fun.

This entry was posted on October 5, 2011 at 9:42 AM and has received 891 views. Comments 4 | Print this entry.

A friend was telling me about a question he saw on an exam and wanted to know my thoughts on it. The exam wanted you to write out the function in pseudo code first and then write it in Java and ColdFusion. The question was pretty basic but it was a good one to think about. Write a method that will accept a sentence as an argument. The method will take this string and reverse the order of the words in the argument.

So following our instructions the first thing we need to do is talk out our thought process for this method.

• create a variable to hold our new string
• Split the argument into words using a space as the delimiter
• loop over out list of words
• take the current word in the loop and prepend it to our new string

That was pretty easy and gives us some really straight forward instructions on how to create our method. First I will write the method in Java. Lucky for us Java has a wonderful class called StringTokenizer. This class will allow us to break our string into tokens and has convenience methods for looping over the tokens and getting the next token. public String reverse(String str){ StringTokenizer st = new StringTokenizer(str); String strReversed = ""; while(st.hasMoreTokens()){ strReversed = st.nextToken() + " " + strReversed; } return strReversed; }

As you might know ColdFusion can leverage any Java class. Because of that our method in ColdFusion should look pretty much the same. If your not familiar with ColdFusion the init method is just a way for us to pass something into the Java constructor. public String function reverseWords(String str){ var st = createObject("java","java.util.StringTokenizer").init(arguments.str); var strReversed = ""; while(st.hasMoreTokens()){ strReversed = st.nextToken() & " " & strReversed; } return strReversed; }

This entry was posted on June 29, 2010 at 8:53 AM and has received 2920 views. Comments 8 | Print this entry.

In Part 1 I looked at why I am using Derby and in Part 2 I looked at how to create custom functions. In the final part of this series we are going to look at the actual code to create our functions.

So in the last part we took a look at writing a replace function. In my example I needed to use a replace function on a database field. SELECT * FROM ModelNumber WHERE REPLACE(number,'-','') IN ('ABC1234','ABC5678') To create that function we have a class that looks like this. package org.vega.derby.functions; public final class StringUtils { public static String replace(String str,String subStr1,String subStr2){ return str.replace(subStr1, subStr2); } } Then I started thinking, what If I need to replace many instances of a string. The function above will only replace the first occurrence. No problem, as I said before we can take this opportunity to create a whole library of functions to use. package org.vega.derby.functions; public final class StringUtils { public static String replace(String str,String subStr1,String subStr2){ return str.replace(subStr1, subStr2); } } public static String replaceAll(String str,String subStr1,String subStr2){ return str.replaceAll(subStr1, subStr2); }

When I actually got back to writing my application I noticed another problem. What if I had to replace more than 1 item? With our current replace method I would have to do something like this. SELECT * FROM ModelNumber WHERE REPLACE(REPLACE(number,'-',''),' ','') IN ('ABC1234','ABC5678') That obviously does not make much sense so what I want to do is write a function that allows to replace multiple strings. In my case I am going to write a function that allows for a regular expression. package org.vega.derby.functions; public final class StringUtils { public static String replace(String str,String subStr1,String subStr2){ return str.replace(subStr1, subStr2); } } public static String replaceAll(String str,String subStr1,String subStr2){ return str.replaceAll(subStr1, subStr2); } public static String reReplace(String str,String regex,String replacement){ return str.replaceAll(regex, replacement); } Now I could do something like this. SELECT * FROM ModelNumber WHERE REREPLACE(number,'[^\w]','') IN ('ABC1234','ABC5678') On top of that I came up with a couple other methods that I thought I could use. package org.vega.derby.functions; public final class StringUtils { /** * Replace the first occurrence of one string and replace it with another in a string * * @param str * @param subStr1 * @param subStr2 * @return */ public static String replace(String str,String subStr1,String subStr2){ return str.replace(subStr1, subStr2); } /** * Replace all occurrences of one string and replace it with another in a string * * @param str * @param subStr1 * @param subStr2 * @return */ public static String replaceAll(String str,String subStr1,String subStr2){ return str.replaceAll(subStr1, subStr2); } /** * Replace all occurrences in a string with another based on regular expression argument * * @param str * @param regex * @param replacement * @return */ public static String reReplace(String str,String regex,String replacement){ return str.replaceAll(regex, replacement); } /** * Will take a string and reverse the order of all of its characters * * @param str * @return */ public static String reverse(String str){ int i; int len = str.length(); StringBuffer sb = new StringBuffer(len); for(i=(len-1); i>=0; i--){ sb.append(str.charAt(i)); } return sb.toString(); } /** * Trims any whitespace from both sides of the string * * @param str * @return */ public static String trim(String str){ return str.trim(); } /** * Repeats a string a number of times based on the count argument * * @param str * @param count * @return str * count */ public static String repeat(String str,int count){ String result = ""; for(int i=1; i<=count; i++){ result += str; } return result; } }

I also want to take the chance to get everyone into the mode of unit testing, so please take a chance watch this public service announcement.

As you can see its pretty easy to create your own functions. On top of being extremely easy you can see its pretty powerful. I just really like being able to create methods in a familiar environment. I have attached my jar file that contains my StringUtils class but you can just as easily create your own. I hope to add some more classes + methods in the future so please give me your suggestions.

This entry was posted on February 17, 2010 at 10:34 PM and has received 3255 views. Comments 0 | Print this entry. Download attachment.

In the 1st part of this series we took a look at using Apache Derby. In the scenario we went over I came to the conclusion that I would need to write some custom functions for Apache Derby to solve my problems. In part 2 of this short series I will walk you through creating your own custom functions.

In other database management systems you have the ability to create user defined functions. You have the same option in Derby only you have to write these functions in Java. If your not a Java expert, don't worry I am not either and I can promise you this is a piece of cake. If you take a look the create function docs you will get the following explanation.

The CREATE FUNCTION statement allows you to create Java functions, which you can then use in an expression.

Continue Reading >>

This entry was posted on February 17, 2010 at 10:10 AM and has received 4714 views. Comments 5 | Print this entry.