Access to method in superclass

[David Colque]

LIKE ACCEDING TO THE METHOD " setSpeed" OF THE SUPERCLASS "Airplane".
Thak you

Attachments:
http://www.ruby-forum.com/attachment/2606/prueba1.rb

 

[RichardOnRails]

LIKE ACCEDING TO THE METHOD " setSpeed" OF THE SUPERCLASS "Airplane".
Thak you

Attachments:http://www.ruby-forum.com/attachment/2606/prueba1.rb

Hi David,

Your access to Airplane::setSpeed is working.

On line 55, you create an Airplane::Jet instance with @speed=0
On line 56, you invoke that setSpeed on the instance with argument 422
so the method on line 38 is called with 422
which in turn invokes Airplane::setSpeed with the argument
422*Multiplier, of 844,
which is then set in @speed of the Airplane::Jet instance
On line 57, you print out the 844

Then on line 57, you invoke

Line 56 set the Jet's speed to 0
Line 57 with argument 422 set the Jet's speed to 422*Multiplier, or
844 and printed it

Line 60 invoked accelerate, which in turn invoked
Line 45 setSpeed(getSpeed()*2)
getSpeed returned your 844, which then got doubled to 1688
which was used as the argument to setSpped, which applied the
Multiplier
so the speed was set to 3376
Line 61 used getSpeed to retrieve the 3376, which then got printed.

All this is confirmed by lines 2 and 2 of your output.

HTH,
Richard

 

[David Colque]

Hi David,

Your access to Airplane::setSpeed is working.

On line 55, you create an Airplane::Jet instance with @speed=0
On line 56, you invoke that setSpeed on the instance with argument 422
so the method on line 38 is called with 422
which in turn invokes Airplane::setSpeed with the argument
422*Multiplier, of 844,
which is then set in @speed of the Airplane::Jet instance
On line 57, you print out the 844

Then on line 57, you invoke

Line 56 set the Jet's speed to 0
Line 57 with argument 422 set the Jet's speed to 422*Multiplier, or
844 and printed it

Line 60 invoked accelerate, which in turn invoked
Line 45 setSpeed(getSpeed()*2)
getSpeed returned your 844, which then got doubled to 1688
which was used as the argument to setSpped, which applied the
Multiplier
so the speed was set to 3376
Line 61 used getSpeed to retrieve the 3376, which then got printed.

All this is confirmed by lines 2 and 2 of your output.

HTH,
Richard

class Jet < Airplane
MULTIPLIER = 2
def initialize
super
end
def setSpeed(speed)
super(speed*MULTIPLIER)
end
def accelerate
# TROUBLE!!!!!!!!
# LIKE ACCEDING TO THE METHOD " setSpeed"
# OF THE SUPERCLASS "Airplane"
Airplane::setSpeed(getSpeed()*2)
end

end

At the time of making it run it leaves the error

ruby prueba1.rb

prueba1.rb:28:in `accelerate': undefined method `setSpeed' for
Airplane:Class (NoMethodError)
from prueba1.rb:43:in `principal'
from prueba1.rb:57
212
844

 

[RichardOnRails]

class Jet < Airplane
MULTIPLIER = 2
def initialize
super
end
def setSpeed(speed)
super(speed*MULTIPLIER)
end
def accelerate
# TROUBLE!!!!!!!!
# LIKE ACCEDING TO THE METHOD " setSpeed"
# OF THE SUPERCLASS "Airplane"
Airplane::setSpeed(getSpeed()*2)
end

end

At the time of making it run it leaves the error>ruby prueba1.rb

prueba1.rb:28:in `accelerate': undefined method `setSpeed' for
Airplane:Class (NoMethodError)
from prueba1.rb:43:in `principal'
from prueba1.rb:57
212
844>Exit code: 1

Hi David,

I can’t see what’s wrong on your program/machine.

I ran the code you posted unchanged and got the following output:
212
844
3376
54016
216064
864256
1696


The first question I’d ask is, what version of Ruby/OS are you
running ... though I doubt that will be too helpful? I’m running:
ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]
WinXP-Pro/SP2

The second question is, are you up to cleaning up code and debugging
it? At http://www.pastie.org/261401, I posted a version of your
program that is closer to what I understand to be “The Ruby Way”. I
don’t understand your purpose, so I can’t do anymore. I hope this
version runs on your machine as it does on mine. I also hope it leads
to a clearer understanding of your program flow.

The version I posted doesn’t produce the same numbers that your
original did, but I don’t want to spend anymore time on it. As I
said, my goal is to help you get closer to “The Ruby Way.”

Best wishes,
Richard

 

[David Colque]

Hi RichardOnRails, thank you very much
Recently I'm learning this language

Ok
Version is
ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]
Operating System is Windows 2003 server (english)


The aim is to bring the code in this java to ruby exactly like this for
learning purposes.


// The code was drawn from the book "Head First Object Oriented Analysis
and Design"
import java.util.*;
class Airplane {
private int speed;

public Airplane() {
}

public void setSpeed(int speed) {
this.speed = speed;
}
public int getSpeed() {
return speed;
}
}

class Jet extends Airplane {
private static final int MULTIPLIER = 2;
public Jet() {
super();
}

public void setSpeed(int speed) {
super.setSpeed(speed * MULTIPLIER);
}

// HERE STAY MY PROBLEM!!!!!!!!!
public void accelerate() {
// Access to method "setSpeed" of class Airplane
super.setSpeed(getSpeed() * 2);
}
}
class FlyTest {
public static void main(String[] args) {
Airplane biplane = new Airplane();
biplane.setSpeed(212);
System.out.println(biplane.getSpeed());
Jet boeing = new Jet();
boeing.setSpeed(422);
System.out.println(boeing.getSpeed());
int x = 0;
while (x<4) {
boeing.accelerate();
System.out.println(boeing.getSpeed());
if (boeing.getSpeed()>5000) {
biplane.setSpeed(biplane.getSpeed() * 2);
} else {
boeing.accelerate();
}
x++;
}
System.out.println(biplane.getSpeed());
}
}

The output is expected is:
212
844
1688
6752
13504
27008
1696

 

[Thomas B.]

Hello.

It's a gotcha in Ruby - there's NO WAY to access ancestor's method
setSpeed from your own method accelerate. As you see, the word super
itself is a call to ancestor's method of the same name as the method you
are currently in. And there's no other use of super, so you cannot call
ancestor's (overridden) method of a different name than the method
you're actually in.

AFAIK they say that you shouldn't need to. If you do, you can refactor
your code and it will be a good thing to do.

TPR.

 

[David Colque]

Hello.

It's a gotcha in Ruby - there's NO WAY to access ancestor's method
setSpeed from your own method accelerate. As you see, the word super
itself is a call to ancestor's method of the same name as the method you
are currently in. And there's no other use of super, so you cannot call
ancestor's (overridden) method of a different name than the method
you're actually in.

AFAIK they say that you shouldn't need to. If you do, you can refactor
your code and it will be a good thing to do.

TPR.

Thank you very much. Then continuous learning …

 

[RichardOnRails]

Hi RichardOnRails, thank you very much
Recently I'm learning this language

Ok
Version is
ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]
Operating System is Windows 2003 server (english)

The aim is to bring the code in this java to ruby exactly like this for
learning purposes.

// The code was drawn from the book "Head First Object Oriented Analysis
and Design"
import java.util.*;
class Airplane {
  private int speed;

  public Airplane() {
  }

  public void setSpeed(int speed) {
    this.speed = speed;
  }
  public int getSpeed() {
    return speed;
  }

}

class Jet extends Airplane {
  private static final int MULTIPLIER = 2;
  public Jet() {
    super();
  }

  public void setSpeed(int speed) {
    super.setSpeed(speed * MULTIPLIER);
  }

        // HERE STAY MY PROBLEM!!!!!!!!!
        public void accelerate() {
    // Access to method "setSpeed" of class Airplane
    super.setSpeed(getSpeed() * 2);
  }}

class FlyTest {
  public static void main(String[] args) {
    Airplane biplane = new Airplane();
    biplane.setSpeed(212);
    System.out.println(biplane.getSpeed());
    Jet boeing = new Jet();
    boeing.setSpeed(422);
    System.out.println(boeing.getSpeed());
    int x = 0;
    while (x<4) {
      boeing.accelerate();
      System.out.println(boeing.getSpeed());
      if (boeing.getSpeed()>5000) {
        biplane.setSpeed(biplane.getSpeed() * 2);
      } else {
        boeing.accelerate();
      }
      x++;
    }
    System.out.println(biplane.getSpeed());
  }

}

The output is expected is:
212
844
1688
6752
13504
27008
1696

Hi David,

OK. I understand your problem. You did the natural thing: you
worked hard to convert the Java program directly into a Ruby program.
It was natural, but it was the wrong approach. Nowadays, the
emphasis in programming is Agile Programming and Test-Driven or
Behavior-Driven Programming. That focuses on writing code in small
pieces and making sure they work correctly. Then add more code, and
make sure that’s right.

So the approach I recommend is:

• Make sure the Java code works as advertised. Check out “Test
FlyTest.java” at http://www.pastie.org/pastes/262610
• Then I show you how to take the first step in “FlyTest1.rb” at
http://www.pastie.org/pastes/262618
• Ditto for the second step in “FlyTest2.rb” at http://www.pastie.org/pastes/262622
• Ditto for the third step in “FlyTest3.rb” at http://www.pastie.org/pastes/262624

In each of the Ruby code I include the Java code in a couple of
comments. I do that for convenience as I try to replicate the Java
functionality in Ruby code. If you don’t like that, you could just as
easily keep the Java code open in a separate window.

As you add code try to make it good Ruby code, nor “Rubyized” Java.
If you don’t know how to express something in Ruby, look at the code
I originally sketched out for you or post a narrow question on the
newsgroup. I recommend you do that rather than posting a lot of code.

For more guidance, check out “Agile Ruby”, “Test-Drive Development
(TDD)” and “Behavior-Driven Development (BDD)” in Google. That’ll
give you some more guidance.

Good luck.

HTH,
Richard