ITEC 320
Lecture 16
Packages (1)
Review
• Questions?
– HW
– Exam
• Nested records
– Benefits
– Downsides
Packages(1)
Objectives
• Packages
– OO in Ada
Packages(1)
Definitions
Which one is Java?
Which one is Ada?
• 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;
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)
Specificatio
n
Store in a .ads file
• 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;
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)
Specificatio
n
Store in a .ads file
• 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;
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
What does this look like?
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;
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)
Specificatio
n
Store in a .ads file
• 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;
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
Packages(1)