Java

Java Joy: Reapply Function With Stream iterate

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Hubert Klein Ikkink

In Java we can use the iterate method of the Stream class to create an unbounded stream based on function invocations. We pass to the iterate method an initial value and a function that can be applied to the value. The first element in the unbounded stream is the initial value, the next element is the result of the function invocation with as argument the value from the previous element and this continues for each new element. Suppose we have a function expressed as lambda expression i → i + 2. When we use this lambda expression with the iterate method and a initial value of 1 we get a stream of 1, 1 → 1 + 2, 3 → 3 + 2, …​.

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Java Joy: Infinite Stream Of Values Or Method Invocations

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Hubert Klein Ikkink

In Java we can use the generate method of the Stream class to create an infinite stream of values. The values are coming from a Supplier instance we pass as argument to the generate method. The Supplier instance usually will be a lambda expression. To give back a fixed value we simply implement a Supplier that returns the value. We can also have different values when we use a method that returns a different value on each invocation, for example the randomUUID method of the UUID class. When we use such a method we can create the Supplier as method reference: UUID::randomUUID.

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Java Joy: Using Functions To Replace Values In Strings

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Hubert Klein Ikkink

Since Java 9 we can use a function as argument for the Matcher.replaceAll method. The function is invoked with a single argument of type MatchResult and must return a String value. The MatchResult object contains a found match we can get using the group method. If there are capturing groups in the regular expression used for replacing a value we can use group method with the capturing group index as argument.

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Java Joy: Using Named Capturing Groups In Regular Expressions

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Hubert Klein Ikkink

In Java we can define capturing groups in regular expression. We can refer to these groups (if found) by the index from the group as defined in the regular expression. Instead of relying on the index of the group we can give a capturing group a name and use that name to reference the group. The format of the group name is ?<name> as first element of the group definition. The name of the group can be used with the group method of the Matcher class. Also we can use the name when we want to reference the capturing group for example with the replaceAll method of a Matcher object. The format is ${name} to reference the group by name. Finally we can use a named capturing group also as backreference in a regular expression using the syntax \k<name>.

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Java Joy: Turn A Pattern Into A Predicate

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Hubert Klein Ikkink

This week at work a colleague showed a nice feature of the Pattern class in Java: we can easily turn a Pattern into a Predicate with the asPredicate and asMatchPredicate methods. The asPredicate method return a predicate for testing if the pattern can be found given string. And the asMatchPredicate return a predicate for testing if the pattern matches a given string.

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Java streams vs for loop

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Ties van de Ven

I had quite a bit of trouble finding a good article about java streams vs for loops under this name so I guess I’ll have to write it myself. In this article I would like to talk about the difference of using the Streaming API and for loops from the standpoint of long term maintainability of the code.

tl;dr: To reduce maintenance costs of your projects, please do consider using the Stream API instead of for loops. It might take some investment in learning to do so, but this investment will pay off in the long run, both for the project and for the engineers.

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Java Joy: Combining Predicates

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Hubert Klein Ikkink

In Java we can use a Predicate to test if something is true or false. This is especially useful when we use the filter method of the Java Stream API. We can use lambda expressions to define our Predicate or implement the Predicate interface. If we want to combine different Predicate objects we can use the or, and and negate methods of the Predicate interfaces. These are default methods of the interface and will return a new Predicate.

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Cucumber-JVM plugin to find unused steps

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Tim te Beek

Cucumber-JVM is a framework for writing end to end tests in natural language, with each line backed by a Java method. Each Java method has a regular expression of natural language lines to match, and lines should only match one such pattern. On a recent assignment I was tasked with modernizing a fairly large cucumber test suite, and going through the steps I found a lot of Java methods that were not being called from the natural language feature files anymore. To identify and remove these unused steps, and prevent any new unused steps in the future, I contributed the following plugin to Cucumber 4.4.0 through: - https://github.com/cucumber/cucumber-jvm/pull/1648 - https://github.com/cucumber/cucumber-jvm/pull/1634

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TestContainers project can make your (integration) test life easier

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Tom de Vroomen

There are those moments you wish you could just start up a real database or system for your (integration) test. In many tests I’ve written I used H2 or HSQLDB to have a data storage for my tests. It starts up quickly and almost supports everything you need to do your repository test or any other test needing data storage. But when your project progresses you start using other ways to store your data other than standard SQL or you use dialect specifics to create your database. This is the moment you discover H2 or HSQLDB is not supporting your database vendor specific features and you can’t get your test running. For example the support for PostgreSQL in H2 or HSQLDB isn’t great, using TIMESTAMP in a SQL script already makes H2 or HSQLDB break. Yes, there are workarounds, but you rather not apply them to keep your code clean and simple. This is the moment you wish it is cheap to start up a real database instance you can test against, so you’re sure your code works in your production environment. You could install the database software locally, make some scripts to initialise the database and clean up afterwards. Or you can make scripts to do this in a Docker container. But what if there’s something which makes this even cheaper to setup?

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