Groovy private fields and methods are not private

Person.groovy

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"}
}

PersonMain out

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

PersonMain.groovy

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
}