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Tag Archives: Java 8

Date/Time Formatting/Parsing, Java 8 Style

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Since nearly the beginning of Java, Java developers have worked with dates and times via the java.util.Date class (since JDK 1.0) and then the java.util.Calendar class (since JDK 1.1). During this time, hundreds of thousands (or maybe millions) of Java developers have formatted and parsed Java dates and times using java.text.DateFormat and java.text.SimpleDateFormat. Given how frequently this has been done ...

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Java 8 : Functional VS Traditional

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The business logic is the same : Given a String expression composed of visits / time like : “1/24h,1..3/3h,5/*” Then the result should be the following list of Strings: “1/24h”, “1/3h”,”2/3h”,”3/3h”, “5/1h”,”5/2h”,”5/3h”,”5/4h”,”5/5h”,until ,”24/1h” So, 2 things need to be solved, the dots and the stars for the visits and for the time. I will use Java 8 , but  I’ll ...

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Java yield-like using Stream API

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Several programming languages, such as Ruby or Python to name a few, provides the yield command. Yield provides an effective way, in terms of memory consumption, to create series of values, by generating such values on demand. More information on Python Yield. Let’s consider a class or method requiring a huge amount of secure random integers. The classical approach would ...

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Default Methods: Java 8’s Unsung Heros

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A few weeks ago I wrote a blog saying that developers learn new languages because they’re cool. I still stand by this assertion because the thing about Java 8 is it’s really cool. Whilst the undoubted star of the show is the addition of Lambdas and the promotion of functions to first class variables, my current favourite is default methods. ...

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Testing code for excessively large inputs

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When writing unit tests we mostly focus on business correctness. We do our best to exercise happy path and all edge cases. We sometimes microbenchmark and measure throughput. But one aspect that is often missed is how our code behaves when the input is excessively large? We test how we handle normal input files, malformed files, empty files, missing files… ...

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The lepidopterist’s curse: Playing with java.time

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Pop quiz: What will be the output of this little program?                     public class DateFun { public static void main(String[] args) { long hours = getHoursOfDay(LocalDate.now(), ZoneId.systemDefault()); System.out.println(hours); } private static long getHoursOfDay(LocalDate date, ZoneId zoneId) { ZonedDateTime startOfDay = date.atStartOfDay(zoneId); Duration duration = Duration.between(startOfDay, startOfDay.plusDays(1)); return duration.toHours(); } } The ...

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Spring 4.1 and Java 8: java.util.Optional

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As of Spring 4.1 Java 8’s java.util.Optional, a container object which may or may not contain a non-null value, is supported with @RequestParam, @RequestHeader and @MatrixVariable. While using Java 8’s java.util.Optional you make sure your parameters are never null.     Request Params In this example we will bind java.time.LocalDate as java.util.Optional using @RequestParam: @RestController @RequestMapping("o") public class SampleController { ...

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Clean JUnit Throwable-Tests with Java 8 Lambdas

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Recently I was involved in a short online discussion on twitter and google+ which concerned the question why the arrival of Java 8 Lambda expressions makes the catch-exception library1 obsolete. This was triggered by a brief announcement that the library won’t be longer maintained as lambdas will make it redundant. The answer I came up with at that time has ...

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Grouping, sampling and batching – custom collectors in Java 8

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Continuing first article, this time we will write some more useful custom collectors: for grouping by given criteria, sampling input, batching and sliding over with fixed size window. Grouping (counting occurrences, histogram) Imagine you have a collection of some items and you want to calculate how many times each item (with respect toequals()) appears in this collection. This can be achieved ...

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