Constructors

A constructor is a piece of code that is executed when an object gets created. The constructor usually will to something like setting initial values but may also even perform more complex operations.

A create statement creates an object by invoking its constructor. Object fields are guaranteed to be initialized to their default values when the constructor is called. If no user-defined default constructor has been implemented, the compiler will implicitly create an empty constructor. This default constructor does nothing.

For class hierarchies, the execution of constructors also follow the given hierarchy: Constructors of parent classes will be executed first, before constructors of child classes get executed. This applies to default constructors as well as to custom constructors.
You can however influence this behavior and replace the implicit call of the parent constructor by an explicit call as described in Calling Constructors of Parent Classes further below.

Declaring a Constructor

You can implement a custom constructor by adding a class operation having the same name as the owning class.

In the example above, both classes Parent and Child contain two custom constructors each (operations marked with orange).

Calling a Constructor

Constructors are called if the name of the created object is followed by parentheses:

create myObject;

create myObject();

create myObject(input.aString);

create local l1 using typeOf(o1);
create local l2() using OutputUsage;
create local l3("local value") using typeOf(o3);   

Example

Assume you have this class structure given:

The following table gives an overview on

{
  "aChildObject" {
     "ancestorProperty": "oldest",
     "grandparentProperty": "older",
     "parentProperty": "old",
     "childProperty": "young"
  }
}

{
  "aChildObject" {
     "ancestorProperty": "oldest",
     "grandparentProperty": "older",
     "parentProperty": "old",
     "childProperty": "younger"
  }
}

Calling Constructors of Parent Classes

If a constructor needs to call the constructor of its parent class explicitly, you can use the keyword super. The super()statement invokes the constructor of the parent class that matches the given parameters.

The super()statement must be the first statement of the constructor.

super();
super(aParameter);