Posts Tagged programming

Java 8: Converting Optional Collection to the Streams API

Although Java 9 has already been released, this post is about converting an optional collection to the Streams API introduced in Java 8.

Suppose some person could have zero, one or more cars and it is represented by the Person class below (some code omitted).

Now we create a list of people and we want to get Mark’s cars.

How can we do that using the Streams API, since the getCars() method return an Optional?

One possibility is to filter people’s list by Mark’s name, filter the Optional if it is present or not and map its wrapped value (our cars list):

At this moment we reached the reason of this blog post. And how can we get all people’s cars? The idea here is to use the flatMap() operation unwrapping the Optional to the collection’s stream when it is present or getting an empty stream when it isn’t present:

We can do better and replace the above solution to be more functional using method references:

If you use IntelliJ IDEA as your favorite IDE, it has an inspection that helps replacing Optional.isPresent() with a functional expression:

P.S. In Java 9, the stream() method was added to the Optional API, so we can rewrite the above stream pipeline into the following one:

In case you are interested, this post on the IntelliJ IDEA blog has some good tips when working with Java 8.

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About the Kotlin programming language

Kotlin is a statically typed language which is fully interoperable with Java.

Recently my friend Andre showed me Kotlin‘s nice syntax and I considered giving it a try.

In the meantime, my friend Leonnardo sent me this nice link which helps migrating from Java to Kotlin easily.

Let’s compare some syntax from Java and Kotlin and see the differences. Suppose we have some employees and we want to group them by their departments.

In Java we create an Employee class, build some employees and use the Streams API to group them by their departments:

In Kotlin we create a data class Employee, build some employees and use the collection built-in groupBy method to group them by their departments:

As you can see, Kotlin has some syntactic sugar that makes it less verbose than Java.

If you haven’t considered trying Kotlin yet, I think it is worth giving it a try.

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35 programming habits that make your code smell

Interesting article about some bad programming practices, including topics like code organization, teamwork, testing and maintenance.

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K Palindromes puzzle

Here we have the K Palindromes puzzle from Javalobby:

You probably already know what a palindrome is: a string to results in the same word, whether read left to right, or right to left. A K Palindrome is when a string can be tranformed into a palindrome by changing K characters at most. Regular palindromes have K=0.

Your challenge today is to write a method which takes a string and a value for k and returns true if it the string qualifies as a K palindrome.

Below is the code in Ruby. Our input string is omississimo and it’s a 0 palindrome String.

The output is true. Do you have another solution? Drop your comments here!

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Minimum difference puzzle in Ruby

Folks, here we are for another puzzle from Javalobby:

Given two arrays, sorted and exactly the same length, write a function that finds a pair of numbers – one from each of the arrays – such that the difference between both is as small as possible.

Suppose our input arrays are [1,2,3,4,5] and [6,7,8,9,10]. Below is my solution in Ruby, it’s a one liner code :-):

The output is [5, 6].

Have another solution? Leave your comments here!

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Balancing arrays puzzle in Ruby

Here we are for another puzzle from Javalobby:

Given an array of numbers, return the index at which the array can be balanced by all numbers on the left side add up the the sum of all numbers of the right side.

For example, an array with [1,5,6,7,9,10] can be balanced by splitting the array at position 4

Here is the solution in Ruby:

The input array [1,5,6,7,9,10] will split the array at position 4, as stated above.

Any other solutions? Drop comments here ๐Ÿ™‚

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Finding the second highest frequency

It’s been a long time since I posted for the last time, but I promise I’ll try to keep this blog up-to-date ๐Ÿ™‚

One of the purposes of this blog is to explore new technologies and recently I’ve been studying Ruby solving some puzzles posted by on JavaLobby.

The problem is about finding the second highest frequency of a character in a String. Below is the Ruby code, using the powerful concept of Ruby closures.

For the input String "aabbbc", the result is "a". I could done it in a more OOP style, but I chose a more concise solution ๐Ÿ™‚

If you have another version in Ruby, feel free to post a comment!

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When to use TestNG or JUnit

There is an interesting discussion between using TestNG or JUnit on Java projects at Javalobby. It’s very worth reading.

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The power of pair programming

Some weeks ago I started doing pair programming with some co-workers basically for two things:

  1. code some tasks of an user story
  2. get familiar with a new software code base

I haven’t had an opportunity to put this technique in practice a lot before, but I can say it was extremely important and benefit for the project. Sometimes I was the driver and sometimes I was the observer. The driver is the person who starts coding and the observer is who starts doing the code review. That point is important: code review.

Pair programming encourages the review of the code. Perhaps you won’t have an opportunity to refactor some code as you have when you are pairing with someone. I think code reviews are important because:

  • Reviews increase code quality, because there are 2 people thinking at the same task at the same time.
  • Refactoring areas arise in the design where improvements are needed
  • When you have the strong support of an IDE (as Eclipse), some refactorings (extract method, extract class, introduce parameter) are highly automated
  • Code is more read than written, two people reading the code can understand a lot more about the code base
  • New ideas arise because of different point of views
  • Questions can be solved by the sum of knowledge of the code base

And you? What’s your experience with pair programming?

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JFileContentManager included in the Softpedia Mac OS software database

100% FREE award granted by Softpedia

I’m proud to announce that JFileContentManager, a software of mine, has been added to Softpedia’s database of software programs for Mac OS. It is featured with a description text, screenshots, download links and technical details on this page.

JFileContentManager has been tested in the Softpedia labs using several industry-leading security solutions and found to be completely clean of adware/spyware components. We are impressed with the quality of your product and encourage you to keep these high standards in the future.

You can see the announce by clicking on the image above. Thanks Softpedia for the award!

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