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Showing posts from April, 2012

Kotlin Language Features Related to Null Handling

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Any software engineer with a Java background would find the null handling features in the Kotlin language interesting. Let's summarize this topic with some examples. Nullable types: In Kotlin, types are non-nullable by default. If you want a variable to be able to hold a null value, you need to explicitly declare its type as nullable using the Type? syntax. For example, String? denotes a nullable string, while String represents a non-nullable string. Safe calls (?.): Kotlin introduces the safe call operator (?.) for handling nullable types. It allows you to safely invoke a method or access a property on a nullable object. If the object is null, the expression returns null instead of throwing a NullPointerException. Example: data class Person(val name: String, val age: Int, val address: String?) fun main() {     // Create a person with a nullable address     val person1 = Person("John Doe", 25, "123 Main Street")     val person2 = Person("Jane Doe", 30,
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Real life TestDrivenDevelopment benefit: Tests as Documentation

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I ve been working on an integration component that listens to LDAP server and notifies applications about changes on LDAP entries. My component searches for LDAP change logs. And a change log has the "targetdn" attribute. Example: targetDn: uid=ND2392,ou=Users,dc=MyCompany There is a business rule about notification process: If Organization Unit is “Special Users”, skip the notification for that change. Example: targetDn: uid=ND2392,ou=Special Users,dc=MyCompany   This changeLog should be skipped because it is about "Special Users" organization unit. I am using a regular expression to parse the targetdn. I isolated the code that does parsing and wrote unit tests for many inputs. Of course I added a unit test for the Business Rule mentioned above. At a point, I thought my regular expression is not good enough and changed it: Old regex: [oO][uU]=[^,]* New regex: [oO][uU]=[^,\s]* I was getting prepared to commit my cod
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Fluent Interface Example in an Enterprise Integration Project

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While working on an enterprise integration project about virtual bank payments, I utilized a simple fluent interface approach. The purpose of the code is creating strongly typed objects from a generic SMO (ServiceMessageObject) instance. Note: In the context of IBM integration technologies, ServiceMessageObject represents the “message”. In our example, it represents a Web Service request. Old Code: if (paymentInfo.getDataObject("totalAmount") != null) { totalAmount = paymentInfo.getDataObject("totalAmount"); DataObject totalAmount2 = totalAmount.getDataObject("totalAmount"); if (totalAmount2.getBigDecimal("amount") != null) { parameters.setAmount(totalAmount2.getBigDecimal("amount")); } String currencyCode = totalAmount2.getString("currencyCode"); parameters.setCurrencyCode(currencyCode); } Byte numberOfInstallments = paymentInfo.getByte("numberOfInstallments"); if (numberOfInstallments !
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Trie Data Structure and Finding Patterns in a Collection of Words

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 I faced a very hard problem recently about finding substrings based on a collection of patterns.  Example For  words = ["Apple", "Melon", "Orange", "Watermelon"]  and  parts = ["a", "mel", "lon", "el", "An"] , the output should be  findSubstrings(words, parts) = ["Apple", "Me[lon]", "Or[a]nge", "Water[mel]on"] . While  "Watermelon"  contains three substrings from the  parts  array,  "a" ,  "mel" , and  "lon" ,  "mel"  is the longest substring that appears first in the string. Note: Number of words and number of parts can be huge! A brute force method or careless usage of Java String methods would make it impossible to handle a large number of words and parts (patterns). Solution Approach Whenever we want to search patterns inside a string, we should think about the Trie data structure:  https://en.wikipedia.
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swapLexOrder: Finding lexicographically largest string

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The following coding question is really amazing: Given a string  str  and array of  pairs  that indicates which indices in the string can be swapped, return the  lexicographically largest  string that results from doing the allowed swaps. You can swap indices any number of times. Example For  str = "abdc"  and  pairs = [[1, 4], [3, 4]] , the output should be swapLexOrder(str, pairs) = "dbca" . By swapping the given indices, you get the strings:  "cbda" ,  "cbad" ,  "dbac" ,  "dbca" . The lexicographically largest string in this list is  "dbca" . Input/Output [execution time limit] 3 seconds (java) [input] string str A string consisting only of lowercase English letters. Guaranteed constraints: 1 ≤ str.length ≤ 10 4 . [input] array.array.integer pairs An array containing pairs of indices that can be swapped in  str  (1-based). This means that for each  pairs[i] , you can swap elements in  str  that have the indices  p
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A Graph Application in Java: Using WordNet to Find Outcast Words

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I'll explain our intent with an example: Let's say we have the following words: horse, zebra, cat, bear, table Which one is the outcast? The table.. But how can a computer system find this? We are talking about the whole English language and any word can be in this list. The number of words in the list can be huge, so the solution should use appropriate data structures and algorithms.  We'll use WordNet which is a graph of English words. It contains the semantic relationships between words and our concern is the "is a" relationship. For our example, we know that horse and cat are both animals. "Table" is not an animal and it is the outcast in this situation. But we even have the ability to tell that horse and zebra is very close. Below is a unit test that shows a high level view of our application in Java: public class OutcastTest {     private WordNet wordNet;     private Outcast outcast;     @Before  
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