itec 320 lecture 16 packages (1). review questions? –hw –exam nested records –benefits...

ITEC 320

Lecture 16Packages (1)

Packages(1)

Review

• Questions?– HW– Exam

• Nested records– Benefits– Downsides

Packages(1)

Objectives

• Packages– OO in Ada

Packages(1)

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?

Packages(1)

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

Packages(1)

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());

}}

Packages(1)

Ada

• 2 pieces– Record for a pair– Function to calculate the distance to the

origin

• File structure– Specification– Body

Packages(1)

Specification

• 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;

Packages(1)

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;

Packages(1)

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?

Packages(1)

Rules

• The specification must be followed to the letter

• All functions / procedures must be implemented

• All return / parameter types must match

Packages(1)

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;

Packages(1)

Specification

• 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;

Packages(1)

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;

Packages(1)

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…

Packages(1)

Privacy

• Java has private variables• Why ?• What do they provide?• How are they used?

Packages(1)

Ada

package PairPkg is -- Public section of package type Pair is private; -- Only type name is public function newPair(x, y: Integer) return Pair; function distanceToOrigin(p: Pair) return Integer; -- Private section of package private -- Code below is NOT visible to client type Pair is record -- Type implementation is private

x, y: Integer; end record

end PairPkg;

What can you do with the

Packages(1)

Package

package body PairPkg is function newPair(x, y: Integer) return Pair is

temp: Pair := (x, y); begin

return temp; end newPair; function distanceToOrigin(p: Pair) return Integer is begin

return p.x + p.y; end distanceToOrigin;

end PairPkg;

What does this look like?

Packages(1)

Client

with ada.integer_text_io; use ada.integer_text_io; with pairpkg; use pairpkg; procedure pairclient is

p: Pair; begin

p := newPair(1, 2); put(distanceToOrigin(p)); p.x := 3; -- Syntax error

end pairclient;

Packages(1)

Specification

• 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;

Packages(1)

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;

Packages(1)

Summary

• Packages in Ada– Specifications– Body