ITEC 320 Lecture 9 Nested records / Packages

Review Project ?’s Records Exam 1 next Friday

Nested records / Packages Outline Nested records

Nested records / Packages Design exercise How do we represent a line mathematically? How do we represent one in Ada?

Nested records / Packages 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);

Nested records / Packages Java/Ada Nested records –How is it implemented in Java? –How is it implemented in Ada?

Nested records / Packages UML Composition –Is a part of Aggregation –Is contained in University Department Faculty Example

Nested records / Packages Arrays What does an array of records like Line mean in terms of –Memory allocation –Syntax

Nested records / Packages Real world example Points Lines Line collection / displayer Images Grid World loader

Nested records / Packages Packages Records are one way of grouping data Packages are one way of grouping functions and procedures

Nested records / Packages 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; Which one is Java? Which one is Ada?

Nested records / Packages 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

Nested records / Packages Java class Pair { int x, y; int distanceToOrigin() // 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()); }

Nested records / Packages Ada 2 pieces –Record for a pair –Function to calculate the distance to the origin File structure –Specification –Body

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

Nested records / Packages 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;

Nested records / Packages 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?

Nested records / Packages Rules The specification must be followed to the letter All functions / procedures must be implemented All return / parameter types must match

Nested records / Packages 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;

Nested records / Packages Specificatio n Tells the compiler what the package does, but not how to do it Store in a.ads file 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;

Nested records / Packages 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;

Nested records / Packages 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…

Nested records / Packages Review Nested records Intro to packages