Where to put methods in a abstract base class - subclasses system

Hi,
I’d like to ask a question on some basic design practice.
When there are methods which are common in some subclasses so I would like to “move them up” in the base abstract class, I would also like to make sure that the ADT concept of the base class itself is not broken. So I don’t want to have methods in the base class that are not general enough to be there. How to resolve this?
For example I create a base abstract class Vehicle. Then I create subclasses Plane and Tanker and realize that the startEnginge() method in them is the same and in order remove the duplicated code, I can put it in Vehicle. But later there may be Bicycle or Sled subclasses which don’t need startEngine().
In a broader sense, I would like to keep the Vehicle class as similar to the real word concept of vehicles as possible. And not evey vehicle have engine of course.
What is the solution?
Extending the class hierarchy by injecting another abstract class between the base and the subclasses? (e.g: VehicleWithEngine)
I suppose I can’t use Interfaces because I need to have the common implemenations as well.
Thanks for any comments in advance,
lemonboston
ps: I am a beginner and don't know the terminology, so if there are programming expression for the followings for example, I would be thankful if someone could help with this too:
- moving common methods up in the class hierarchy
- injecting a class in the hierarchy
- abstract base class - subclasses system

lemonboston wrote:
Hi,
I’d like to ask a question on some basic design practice.
When there are methods which are common in some subclasses so I would like to “move them up” in the base abstract class, I would also like to make sure that the ADT concept of the base class itself is not broken. So I don’t want to have methods in the base class that are not general enough to be there. How to resolve this?
You are talking about code.
Instead you need to talk about the design.
The base class represents conceptually a 'type' of something. That 'type' defines behavior. That behavior is what goes in the base class nothing else (in terms of design.)
If you have common functionality which does not fit into the definition (design) of the 'type' then you put it in another class and use (composition) that class in the sub class.
For example I create a base abstract class Vehicle. Then I create subclasses Plane and Tanker and realize that the startEnginge() method in them is the same and in order remove the duplicated code, I can put it in Vehicle. But later there may be Bicycle or Sled subclasses which don’t need startEngine(). No that is not how it works.
You have specific examples of some vehicles and then you need to manage those types generically. That is the first step.
Second step is then to determine what the exact 'type' is that you want to manage. And you use the requirements of the need to create the 'type'.
Then you look at the specific examples to determine how they will meet the needs of the type.
Thus if I have an application that must start the engines of all the vehicles in the city then I must have a vehicle class which has startEngine.
But if I have an application that manages vehicles as inventory (like a retail store) and then decide that because my examples both have engines that I might as well move it into the base class. In that case there is no 'need' for the application to manage starting vehicles. The fact that both have engines is irrelevant.
So looking back at your example you have stated functionality about your specific types but you have not stated anything about why your application needs to deal with that functionality generically.
Another way to think about it is that you do not put the shared functionality in the base because you can but rather because you must.

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"defaultarg.cpp", line 6: Error: StringBase::StringBase(const StringBase&) is not accessible from __dflt_argA().
1 Error(s) detected.
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#define CONSTSTRING_H
#include "stringbase.h"
class ConstString : public StringBase
public:
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What you are trying to do is very common and the process you described is exactly how map the class. I will summarize a couple of points for mapping this scenario.
1. You only need to import Address in and map it. If AbstractDomainObject is imported into the Mapping Workbench make sure that it is disabled. The abstract class is only required on the project's CLASSPATH.
2. You should not enable inheritance for the Address class. Inheritance is for situations where the abstract base class has its own independent table. I am assuming that your Address class has its own table that contains fields for all of the attributes it needs along with those of the abstract base class.
Assuming these conditions are met then TopLink will work fine with you Address class just as if it had all of the inherited attributes directly.
If you are still having trouble take a look through your generated project (XML or Java) to ensure that mappings exist in Address for All attributes. If the project looks good then I am at a loss. Customers have been using this pattern of use for over 5 years with TopLink and Java inheritance.
Cheers,
Doug

Abstract/ concrete class questions/problems

I am new to java and working on a abstract problem. I'm getting several errors. Here is the code I have so far for the abstract class. I commented out the super and it compiles but I'm not sure if it correct. I'm suppose to create a abstract base class Animal. Single constructor requires String to indicate type of animal which then is stored in an instance variable. I also have to add a few methods (describe(), move(), etc).
public abstract class Animal
     public Animal(String type)
          //super(type);
     public abstract String describe();
     public abstract String sound();
     public abstract String sleep();
     public abstract String move();
}

thanks for the replies. I modified my code but I have a few more errors I can't figure out. Can you browse the code and help point me in the right direction.
Here are the errors I get
cannot find symbol
symbol : constructor Cat(java.lang.String,java.lang.String)
location: class Cat
cannot find symbol
symbol : constructor Robin(java.lang.String)
location: class Robin
abstract base class:
public abstract class Animal
     String type;
     public Animal(String type)
       this.type = type;
     public abstract String describe();
     public abstract String sound();
     public abstract String sleep();
     public abstract String move();
}concrete class
public class Cat extends Animal
     private String name;
     protected String breed;
     public Cat()
       super("Cat");
     public String describe()
          return new String(",a breed of Cat called");
     public String sound()
          return new String("Meow");
     public String sleep()
          return new String("Kitty is having purfect dreams!");
     public String move()
          return new String("This little Kitty moves fast!");
}another abstract class
public abstract class Bird extends Animal
     protected String breed;
     public Bird()
       super("Bird");
     public abstract String move();
}here is the abstract test program itself
public class AbstractTest
     public static void main(String[] args)
          Cat cat = new Cat("Kitty", "Angora");
          Robin bird = new Robin("Rockin");
          System.out.println("Form the cat:   ");
          System.out.print("This is:     "); cat.describe();
          System.out.print("Sound:       "); cat.sound();
          System.out.print("Sleeping:    "); cat.sleep();
          System.out.print("Moving:      "); cat.move();
          System.out.println("\n");
          System.out.println("For the robin:     "); bird.describe();
          System.out.print("This is:             "); bird.sound();
          System.out.print("Sound:               "); bird.sleep();
          System.out.print("Moving:              "); bird.move();
          System.out.print("\n");
          System.out.println("nEnd of program.");
}

Base classes with Collection attributes

I have a question. Suppose I have a base class A, an abstract base class
to be exact, and subclasses B and C. Assume A has an attribute of
Collection type, let's call it collectionImpl. Now I would like subclasses
B and C to be able to have elements of different types along the lines of
what I've outlined below.
Strictly speaking, class A wouldn't have to be PC, since I primarily care
of B and C but I wanted to show the structure.
<class name="A" persistence-capable-superclass="A">
<field name="collectionImpl">
<collection element type="someType"/>
</field>
</class>
<class name="B" persistence-capable-superclass="A">
<field name="collectionImpl">
<collection element type="someOtherType"/>
</field>
</class>
So, how would one express this?
Scott

Understood. Now for bit more clarification. Given my earlier example, what
if classes A, B and C implement the java.util.Collection interface. Does
Kodo have in issue with that? I know Kodo has this ProxyCollection stuff
but I don't really want to do that, nor do I think I really need to given
what I'm trying to accomplish.
The issue I'm having now is that the Kodo Enhancer is complaining that no
element-type is declared when I have an attribute of class type B for
example (implementing java.util.Collection) even though an element type is
declared for the that actual Collection object held in the base class of B
(A).
<class name="A" requires-extent="false">
<field name="impl">
<collection element-type="SomeType"/>
<extension vendor-name="kodo" key="ordered" value="true"/>
</field>
</class>
<class name="B" persistence-capable-superclass="A"
requires-extent="false"/>
Class "A" extends java.util.AbstractSet, impl is an instance of
java.util.Collection.
All this was working quite well until I made some updates recently
although the basic implementation is the same. Logically I don't know what
I might have done to cause the new error message.
I'm using v2.5.2 BTW.
Scott
Stephen Kim wrote:
The one thing to note is that if you do not make A persistent capable,
you cannot persist fields -declared- in A or query starting from A.
Scott A. Leschke wrote:
Can I acheive the same effect by making A be non-PC and provide a abstract
protected method that will be used by a to access the collection
implemented in the sub-classes as you suggest (ie. Collection
getCollectionImpl())?
Steve Kim
[email protected]
SolarMetric Inc.
http://www.solarmetric.com

How to call a method of a base class if the base class is abstract...

This is my sample code>>>>
abstract class b {
     public void display() {
          System.out.println("I am in Base Class");
class test extends b {
     public static void main(String[] args) {
          test obj = new test();
          obj.display();
     public void display() {
          System.out.println("I am in Derived Class");
I want to call base class version of display with derived class object.........is it possible....

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Enough with the friggin' zombie threads already!

Explizit using methods of base class

when using a base class reference from an abstract class A and creating an object of subclass B
A ref_A = new B();
assuming we have implemented the method m() in A and B, then
ref_a.m()
calls Method m of subclass B
(dynamic binding, fine)
Is there a possibility to force explicitely the call of method m of superclass A.
(i mean not a call from Method m in B with super())

are you absolutely sure ?I am sure. Perhaps you are thinking of C++ (and if you're not, I am!) where you can write: ref_A.A::m(),
but there's no way from the client code to do that in Java. If you really need to do this, your
design of A should reflect it:
public abstract class A {
    public final void mOldSchool() {...}
    public void m() { mOldSchool(); }
public class B extends A {
    public void m() {...}
}I agree with Kayaman, though: question your design. In the abstract, this is a shakey design.

Calling a method from an abstract class in a seperate class

I am trying to call the getID() method from the Chat class in the getIDs() method in the Outputter class. I would usually instantiate with a normal class but I know you cant instantiate the method when using abstract classes. I've been going over and over my theory and have just become more confused??
Package Chatroom
public abstract class Chat
   private String id;
   public String getID()
      return id;
   protected void setId(String s)
      id = s;
   public abstract void sendMessageToUser(String msg);
Package Chatroom
public class Outputter
public String[] getIDs()
     // This is where I get confused. I know you can't instantiate the object like:
        Chat users=new Chat();
        users.getID();
I have the two classes in the package and you need to that to be able to use a class' methods in another class.
Please help me :(

I have just looked over my program and realised my class names are not the most discriptive, so I have renamed them to give you a clearer picture.
package Chatroom
public abstract class Chatter
private String id;
public String getID()
return id;
protected void setId(String s)
id = s;
I am trying to slowly build a chatroom on my own. The Chatter class is a class that will be used to represent a single logged in user and the user is given an ID when he logs in through the setId and getID() methods.
package Chatroom;
import java.util.Vector;
public class Broadcaster
private Vector<Chatter> chatters = new Vector<Chatter>();
public String[] getIDs()
// code here
The Broadcaster class will keep a list of all logged-in users keeps a list of all the chats representing logged-in users, which it stores in a Vector.I am trying to use the getIDs() method to return an array of Strings comprising the IDs of all logged-in users, which is why im trying to use the getID() method from the Chat class.
I apologise if I come across as clueless, it's just I have been going through books for about 4 hours now and I have just totally lossed all my bearings

Where to put javascript code?

Hello,
I am trying to set some columns in a list as "read-only" and is using the following code:
<script type=”text/javascript”>
function SetReadOnly()
var elements=document.getElementById(’4_ctl00_ctl00_TextField’);
elements.readOnly=true;
_spBodyOnLoadFunctionNames.push(“SetReadOnly()”);
</script>
But I am not sure where to put the code in. Should I put it in the space in Content Editor Web Part,
or through a link to a txt file, or in "Edit HTML"? I've tried them but none works.
Thanks a lot!
Patrick

You can try this:
1) Open your Sharepoint List. Go to List edit view.
2) On right side of Ribbon you will find "Form Web Parts" option as shown in figure.
3) Choose your List form which you want to edit.
4) Now you can add web part in new window.
5) Add Content Editor Web part.
6) In content editor web part add the path of your "txt" file in which you have written your script, for eg.
<!DOCTYPE html>
<html>
<body>
<script type=”text/javascript”>
function SetReadOnly()
var elements=document.getElementById('4_ctl00_ctl00_TextField');
elements.readOnly=true;
_spBodyOnLoadFunctionNames.push("SetReadOnly()");
</script>
</body>
</html>
I haven't tried this method so I am not sure but hope it works...:D
***If my post is answer for your query please mark as answer***
***If my answer is helpful please vote***

Where to put methods in a abstract base class - subclasses system

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