Zoltán Hernyák High-Level Programming Languages II. Object-Oriented Programming in practice ZOLTÁN HERNYÁK High-Level Programming Languages II. draft version 2014.03.14 Zoltán Hernyák High-Level Programming Languages II. Object-Oriented Programming in practice Eger 2012 Author Hernyák Zoltán PhD associate professor Eszterházy Károly College Lector Table of contents Tartalom Table of contents .................................................................................................................. 3 1. Introduction .................................................................................................................. 8 2. The history of OOP ......................................................................................................12 3. The principles of OOP ..................................................................................................15 4. The classification of imperative languages .................................................................18 5. A simple example for an OOP problem .......................................................................20 6. Data hiding ..................................................................................................................24 6.1. To protect the value of a field ...............................................................................26 6.2. A solution with methods .......................................................................................27 6.3. Error indicating ....................................................................................................30 6.4. Protected instead private .....................................................................................32 6.5. Why is the private the default protection level? ..................................................33 6.6. Property ................................................................................................................34 6.7. When we might think no protection is needed .....................................................37 6.8. Writeable once fields .............................................................................................38 6.9. Read only fields .....................................................................................................40 6.10. A more effective solution ...................................................................................42 7. Methods ........................................................................................................................43 7.1. Instance-level methods .........................................................................................44 7.2. Handling the actual instance ...............................................................................46 8. The function Main ........................................................................................................50 9. The constructors ..........................................................................................................53 9.1. Constructors during the instantiation .................................................................54 9.2. Creating a constructor ..........................................................................................55 9.3. Creating several constructors ...............................................................................56 9.4. Lack of constructor ...............................................................................................57 9.5. Checking the parameters .....................................................................................58 9.6. Write-once fields ...................................................................................................59 9.7. A property with two different protection level .....................................................60 9.8. The real write-once fields .....................................................................................61 9.9. Constants ..............................................................................................................62 10. The data members ....................................................................................................64 10.1. Instance level fields ...........................................................................................64 10.2. Class level fields ................................................................................................66 10.3. Constants ...........................................................................................................67 11. The inheritance ........................................................................................................69 11.1. The inheritance of the fields .............................................................................69 11.2. Problems around fields inheritance ..................................................................71 11.3. The keyword ‘base’ ............................................................................................75 11.4. Inheritance of the methods ...............................................................................76 11.5. The problems around method inheritance ........................................................78 11.6. The methods and the ‘base’ ...............................................................................81 11.7. The real problems around the inheritance of the methods ..............................82 12. Type compatibility ....................................................................................................84 12.1. The consequences of the type compatibility .....................................................85 12.2. The Object class .................................................................................................90 12.3. The static and the dynamic type .......................................................................91 12.4. The operator ‘is’ .................................................................................................92 12.5. Early binding and its problems .........................................................................92 13. The virtual methods .................................................................................................97 13.1. The override and the property ..........................................................................98 13.2. Other rules of override ......................................................................................99 13.3. Manual late binding – the ‘as’ operator .......................................................... 101 13.4. When the type cast is the only help ................................................................ 105 13.5. Typecast is not an ultimate weapon ............................................................... 105 13.6. The story of kangaroos .................................................................................... 108 14. Problems with the constructors ............................................................................. 110 14.1. The constructor call chain ............................................................................... 111 14.2. Constructor identification chain ..................................................................... 112 14.3. To call an constructor with “this” ................................................................... 115 14.4. To call an own constructor and the constructor identification chain ............. 118 14.5. To call an ancestor class constructor explicitly with ‘base’ ............................ 118 14.6. Class-level constructors .................................................................................. 120 14.7. Private constructors ........................................................................................ 123 14.8. The keyword ‘sealed’ ....................................................................................... 124 14.9. The Object Factory .......................................................................................... 126 15. The indexer ............................................................................................................. 130 16. Namespaces ............................................................................................................ 136 17. The Object class as the ancestor ............................................................................ 144 17.1. GetType() ......................................................................................................... 144 17.2. ToString() ........................................................................................................ 145 17.3. Equals() ........................................................................................................... 146 17.4. GetHashCode() ................................................................................................ 147 17.5. Boxing – Unboxing .......................................................................................... 148 17.6. The list of Object ............................................................................................. 151 17.7. An object parameter ........................................................................................ 154 18. The abstract classes ............................................................................................... 157 19. VMT and DMT.......................................................................................................