ITEC 320

1. ITEC 320 Lecture 9 Nested records / Packages

2. Review • Project ?’s • Records • Exam 1 next Friday

3. Outline • Nested records

4. Design exercise • How do we represent a line mathematically? • How do we represent one in Ada?

5. Code type Pair is record x: Integer; y: Integer; end record; type Line is record start: Pair; end: Pair; end record; myLine: Line; begin myLine.start.x:= 1; myLine.start.y:= 2; myLine.end:= (3, 4); put(myLine.start.x); put(myLine.end.x);

6. Java/Ada • Nested records • How is it implemented in Java? • How is it implemented in Ada?

7. UML • Composition • Is a part of • Aggregation • Is contained in University Department Faculty Example

8. Arrays • What does an array of records like Line mean in terms of • Memory allocation • Syntax

9. Real world example • Points • Lines • Line collection / displayer • Images • Grid • World loader

10. Packages • Records are one way of grouping data • Packages are one way of grouping functions and procedures

11. Which one is Java? Which one is Ada? Definitions • Client • Uses the class and its methods • Routine or package that uses the types and routines defined in package P • Examples • With ada.text_io; use ada.text_io;

12. Ada “Classes” • Records store information • Procedures work with records / other data • Put the two together and you have the Ada version of classes • Contain • Procedures • Types

13. Java class Pair { intx, y; intdistanceToOrigin() // How far to origin { return Math.abs(x) + Math.abs(y); } } // Client for class Pair class PairClient { public static void main(String[] args) { Pair p; p = new Pair(); p.x = 1; p.y = 2; Sop(p.distanceToOrigin()); } }

14. Ada • 2 pieces • Record for a pair • Function to calculate the distance to the origin • File structure • Specification • Body

15. Store in a .ads file Specification • Tells the compiler what the package does, but not how to do it package PairPkg is type Pair is record x, y: Integer; end record function distanceToOrigin(p: Pair) return Integer; end PairPkg;

16. Body • Contains the code for a certain package’s procedures / functions package body PairPkg is function distanceToOrigin(p: Pair) return Integer is begin return abs p.x + abs p.y; end distanceToOrigin; end PairPkg;

17. Ada / Java • Java classes (1 file) • Ada method (2 files) • What are the benefits / downsides of each approach? • How does Java sort of provide the same idea that Ada does?

18. Rules • The specification must be followed to the letter • All functions / procedures must be implemented • All return / parameter types must match

19. Use • Without the use statement, you have to fully-qualify the package name with pairpkg; procedure pairclient is p: pairpkg.Pair; begin p.x:= 1; p.y:= 2; put(pairpkg.distanceToOrigin(p)); end pairclient;

20. Store in a .ads file Specification • Tells the compiler what the package does, but not how to do it package PairPkg is type Pair is private; function distanceToOrigin(p: Pair) return Integer; private type Pair is record x, y: Integer; end record; end PairPkg;

21. Body • Contains the code for a certain package’s procedures / functions package body PairPkg is function distanceToOrigin(p: Pair) return Integer is begin return abs p.x + abs p.y; end distanceToOrigin; end PairPkg;

22. Compilation • Rule of thumb • Keep it all in the same directory • Some way of pointing where to look for specifications / bodies • Compiler does the work for you • Automatically pulls in packages thanks to the with statement • Take a look at the files produced and think about why they are there…

23. Review • Nested records • Intro to packages