DDevelopment & Design

Friday hackathon

Every month we have a Friday Hackathon, where we can code or create anything we want. That’s for the purpose of evaluating new technologies, doing crazy stuff or just having fun.

Beneath that we develop our skills and gain new experience.

Today we have 5 teams, that are doing following projects in various technologies:

  • Ping-pong scoring – we play ping pong a lot, so an app is a must! – Java (Dropwizard), Mongo
  • TouK’s library – we have dozens of books but currently we have a chaos who lends what – Clojure
  • ToukApi – access all internal data (about people, salaries, holidays, auth, projects people are in etc) through REST api – vert.x
  • ID / Drivers license recognition on Mobile – just shoot a photo of an ID and have all data and photo in a few seconds – Kotlin, Android
  • jaIde – I’m going for a sandwich – you can inform other employees that you go for a morning sandwich – that means – Mr Sandwich has just arrived at the kitchen – it’s like a snowball, the more people go for a sandwich the more confident you can be that there are actually sandwiches waiting :) – Swift/Scala/Java

At 4:30 PM we have hackathon summary. Let’s see what projects we will manage to accomplish…

 

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DDevelopment & Design

Private fields and methods are not private in groovy

I used to code in Java before I met groovy. Like most of you, groovy attracted me with many enhancements. This was to my surprise to discover that method visibility in groovy is handled different than Java!

Consider this example:

class Person {
private String name
public  String surname

private Person() {}

private String signature() { "${name?.substring(0, 1)}. $surname" }

public String toString() { "I am $name $surname" }
}

How is this class interpreted with Java?

  1. Person has private constructor that cannot be accessed
  2. Field "name" is private and cannot be accessed
  3. Method signature() is private and cannot be accessed

Let's see how groovy interpretes Person:

public static void main(String[] args) {
def person = new Person()   // constructor is private - compilation error in Java
println(person.toString())

    person.@name = 'Mike'       // access name field directly - compilation error in Java
println(person.toString())

    person.name = 'John'        // there is a setter generated by groovy
println(person.toString())

    person.@surname = 'Foo'     // access surname field directly
println(person.toString())

    person.surname = 'Bar'      // access auto-generated setter
println(person.toString())

println(person.signature()) // call private method - compilation error in Java
}

I was really astonished by its output:

I am null null
I am Mike null
I am John null
I am John Foo
I am John Bar
J. Bar

As you can see, groovy does not follow visibility directives at all! It treats them as non-existing. Code compiles and executes fine. It's contrary to Java. In Java this code has several errors, pointed out in comments.

I've searched a bit on this topic and it seems that this behaviour is known since version 1.1 and there is a bug report on that: http://jira.codehaus.org/browse/GROOVY-1875. It is not resolved even with groovy 2 release. As Tim Yates mentioned in this Stackoverflow question: "It's not clear if it is a bug or by design". Groovy treats visibility keywords as a hint for a programmer.

I need to keep that lesson in mind next time I want to make some field or method private!