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