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Abstract Data Types and Object-Oriented Programming

Abstract Data Types and Object-Oriented Programming. Juan Carlos Guzmán CS 3123 Programming Languages Concepts Southern Polytechnic State University. Process Abstraction.

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Abstract Data Types and Object-Oriented Programming

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  1. Abstract Data Types and Object-Oriented Programming Juan Carlos Guzmán CS 3123 Programming Languages Concepts Southern Polytechnic State University PLC Summer 2002

  2. Process Abstraction • Abstraction is the process of taking away or removing characteristics from something in order to reduce it to a set of essential characteristics1 • For processes • Essential characteristics • name • Type signature • Environment variables used/side-effected • Non-essential characteristics • Implementation • Abstractions are used through “interfaces”, and are supported by their implementation 1http://whatis.techtarget.com PLC Summer 2002

  3. Encapsulation • Data cannot be abstracted independently from the processes that act upon them • Collections of programs can be organized along with the data they manipulate • For abstraction of Programs+Data • For independent compilation of “modules” PLC Summer 2002

  4. Modules • Groups of logically related subprograms and data • This is the concept of encapsulation • Another opportunity for abstraction • Interface is composed of • Data • Procedures • Not all data or procedures are visible through the interface •  information hiding PLC Summer 2002

  5. Information Hiding • As part of the abstraction barrier, the following hidings may be in place • Procedures • The implementation of the procedure is hidden, only the interface is known • Types • The type may be “opaque” • Names • names (of variables, constants, procedures, etc.) may be hidden or available • Note how Ada separates interfaces from their implementation PLC Summer 2002

  6. Abstract Data Types in Languages • Every data type can be considered an “Abstract Data Type” • Integers • Floating Points • Pairs • Lists • Bignums • etc. • Can users create ADT’s? PLC Summer 2002

  7. ADT in Languages • Ada ==> packages • C++ ==> classes • Java ==> classes • Modula2 ==> modules PLC Summer 2002

  8. Interface Operations create(stack) destroy(stack) empty(stack) push(stack,element) pop(stack) top(stack) Values MAX_SIZE Types STACKTYPE Implementation Definitions for Operations STACKTYPE Initialization for such a data structure How are stacks implemented? Arrays Lists Hash tables ADT Example (Stack) PLC Summer 2002

  9. Parameterized ADT • Type systems put restrictions to ADT’s • Your book’s stack ADT works on integers • However stacks operate on any data • stacks of reals • stacks of stacks of integers • Parameterize the ADT with respect to certain key types • parameterize the stack ADT with respect to the element type PLC Summer 2002

  10. Parameterized ADT • Parameterized ADT’s are specifications that need these parameter types to become real ADT’s • Supply the element type to the generic stack ADT • Each instantiation of the parameterized ADT usually results in code specific to the supplied types • This shouldn’t be, but it’s a consequence of type systems, and the way data is implemented PLC Summer 2002

  11. Parameterized ADT in Languages • Ada ==> generic packages • C++ ==> templates • Java ==> tba in v.1.5 • Modula2 ==> modules PLC Summer 2002

  12. Example • Page 446 of your book PLC Summer 2002

  13. Object-Oriented Programming • ADT’s, plus • Inheritance • A “better” type system PLC Summer 2002

  14. Vocabulary • Class ==> ADT • Object ==> ADT instance • Derived class or sub class ==> A class that is based on another • Parent class ==> A class on which another is based • method ==> a procedural element of a class • message ==> a call to a method • property ==> a non-procedural element of a class PLC Summer 2002

  15. Inheritance • Not all ADT’s are defined at the same level • Hierarchy of data types • Newly defined data types can make use of existing ADT’s • take useful definitions • add new ones • override others PLC Summer 2002

  16. Polymorphism • The type system has been extended to allow for “subtypes” • objects from derived classes are accepted in contexts where the parent class is declared • the actual class of objects • is not known at compile time • will be known at run time • Note that deriving does not always result in subtyping PLC Summer 2002

  17. Implementation vs Interface Inheritance • Interface inheritance • only the interface of the parent class is known to derived classes • Implementation inheritance • the implementation details are also known to derived classes • With implementation inheritance, changing the implementation of the parent class will require recompilation of derived classes PLC Summer 2002

  18. Single vs Multiple Inheritance • Multiple Inheritance has its issues on method and property duplication • Should a language allow multiple inheritance • C++ does • Java does not PLC Summer 2002

  19. Allocation & Deallocation • Allocation on the stack or on the heap • Explicit or implicit deallocation PLC Summer 2002

  20. Dynamic vs Static Binding • When do bindings of messages to methods take place? • Static ==> static class • Dynamic ==> dynamic class PLC Summer 2002

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