Creating Objects of Base and Complex Types

The most basic features of each language are creating instances of classes and setting values.

• With the set assignment statement, it is possible to create objects of base types like String, Integer, Float, Boolean, and DateTime

• whereas objects of complex types need to be instantiated (created) first with the create statement - that is creating an instance of the corresponding class. Once the instance of the class (the object) has been created, it can store data in its attributes.

Creating Base Types with the set Assignment Statement

The following examples shows how to use the set assignment statement to create base type objects.

set aString = "Hello World!"; 
set anInteger = 12345; 
set currentDate = currentDateTime();

Base type objects need not to be instantiated, they are created by using the set assignment statement to directly assign a value to the variable.

Creating Arrays by Appending Items

You can create arrays using the create statement (see action script example below):

create anArray;
append "Hello World!" to anArray;

Most of the time the xUML Runtime will create the array implicitly on appending the first item. There is one exception to this rule, though: Arrays that contain array elements having a complex type with multiplicity.

Let's assume you have an array of complex type ArrayElement and this complex type has a property subArray with multiplicity 0..*.

• What you can do, if subArray is NULL:

//The reference subArray is changed to point to anotherArray.
set array1[0].subArray = anotherArray;

• What you can't do, if subArray is NULL:

append "something" to array1[0].subArray;

In this case (get statement on the right side of a statement), the Runtime will throw a get error for array1[0].subArray.

Creating Objects of Complex Type

The following example shows how to use the create statement to create objects of complex type.

Scalar base type objects are never created using the create statement (see Creating Base Types with the set Assignment Statement above).

 create simpleObject;

In the following cases, objects need to be created with the create statement:

• You want to explicitly create an instance of a class.

• Result objects of an iteration over an action script need to be created.

In the following cases, the create statement is not necessary:

• Adapters may create objects of any type. Those objects are implicitly created by the adapter and do not need to be created explicitly, e.g. the result set of an SQL query.

• When having related classes, the instantiation of intermediate objects is not mandatory.
  In the example below, ClassA has an attribute b, which is of type ClassB (see association). ClassB in turn has a string attribute named aString.

  

  When creating an instance of the top-level class ClassA, the lower classes are instantiated implicitly, so the action script below would be fine.

  CODE

  create objectOfClassA;
  set objectOfClassA.b.aString ="Hello World!";