D.1 Objects as a Programming Concept
D.1.1 Outline the general nature of an object.
An object as an abstract entity and its components—data and actions.
Familiar examples from different domains might be people, cars, fractions, dates, and music tracks.
D.1.2 Distinguish between an object (definition, template or class) and instantiation.
Students must understand the difference in terms of code definitions, memory use and the potential creation of multiple instantiated objects.
D.1.3 Construct unified modelling language (UML) diagrams to represent object designs.
D.1.4 Interpret UML diagrams.
D.1.5 Describe the process of decomposition into several related objects.
A simple example with 3–5 objects is suggested. Examples related to D.1.1 could be employers, traffic simulation models, calculators, calendars, media collections.
D.1.6 Describe the relationships between objects for a given problem.
The relationships that should be known are dependency (“uses”), aggregation (“has a”) and inheritance (“is a”).
D.1.7 Outline the need to reduce dependencies between objects in a given problem.
Students should understand that dependencies increase maintenance overheads.
D.1.8 Construct related objects for a given problem.
In examinations problems will require the students to construct definitions for no more than three objects and to explain their relationships to each other and to any additional classes defined by the examiners.
D.1.9 Explain the need for different data types to represent data items.
The data types will be restricted to integer, real, string, and Boolean.
D.1.10 Describe how data items can be passed to and from actions as parameters.
Parameters will be restricted to pass-by-value of one of the four types in D.1.6. Actions may return at most one data item.
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