DDevelopment & Design

All field constructor in Groovy

TupleConstructor annotation in Groovy generate constructors for class with each of its properties (eventually also fields). The class below@TupleConstructor(includeFields = true)class Person {   String firstName   String lastName&nb…

TupleConstructor annotation in Groovy generate constructors for class with each of its properties (eventually also fields). The class below

@TupleConstructor(includeFields = true)
class Person {
   String firstName
   String lastName
   private boolean male
}

will have constructors: Person(), Persion(String), Person(String, String) and Person(String, String, boolean). You could test it using code below.

class TupleConstructorTest extends GroovyTestCase{
    @Test
    void testSimpleTupleConstructorShouldGenerateConstructor() {
        assertScript '''
            import groovy.transform.TupleConstructor
            @TupleConstructor(includeFields = true)
            class Person {
                private final String firstName
                private final String lastName
                private final boolean male
                String toString(){ "$firstName $lastName $male" }
            }            
            assert Person.constructors.size() == 4
            assert new Person().toString() == 'null null false'
            assert new Person('John').toString() == 'John null false'
            assert new Person('John','Smith').toString() == 'John Smith false'
            assert new Person('John','Smith', true).toString() == 'John Smith true'
        '''
    }
}

I almost always create classes with all private final fields and generate constructior with all fields using my IDE.

So I have prepared new transformation AllFieldConstructor which bases on TupleConstructor and generates only constructor with all fields as parameters.

class AllFieldConstructorTest extends GroovyTestCase{
    @Test
    void testSimpleTupleConstructorShouldGenerateConstructor() {
        assertScript '''
            import com.blogspot.przybyszd.transformations.AllFieldConstructor
            @AllFieldConstructor
            class Person {
                private final String firstName
                private final String lastName
                private final boolean male
                String toString(){ "$firstName $lastName $male" }
            }
            assert Person.constructors.size() == 1
            assert new Person('John','Smith', true).toString() == 'John Smith true'
        '''
    }
}

The sources are available here

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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!