Java - Abstract class to contain variables

Question

Is it good practice to let abstract classes define instance variables   public abstract class ExternalScript extends Script        String source       public abstract void setSource String file        public abstract String getSource        The sub class  ExternalJavaScript class  would then automatically get the source variable but I feel it s easier to read the code if all the sub classes themselves define the source  instead of from inheritance    What is your advice    Adam

User · Answer

Of course   The whole idea of abstract classes is that they can contain some behaviour or data which you require all sub-classes to contain   Think of the simple example of WheeledVehicle - it should have a numWheels member variable   You want all sub classes to have this variable    Remember that abstract classes are a very useful feature when developing APIs  as they can ensure that people who extend your API won t break it

User · Answer

Of course   The whole idea of abstract classes is that they can contain some behaviour or data which you require all sub-classes to contain   Think of the simple example of WheeledVehicle - it should have a numWheels member variable   You want all sub classes to have this variable    Remember that abstract classes are a very useful feature when developing APIs  as they can ensure that people who extend your API won t break it

User · Answer

I would have thought that something like this would be much better  since you re adding a variable  so why not restrict access and make it cleaner  Your getter setters should do what they say on the tin   public abstract class ExternalScript extends Script        private String source       public void setSource String file            source   file             public String getSource             return source            Bringing this back to the question  do you ever bother looking at where the getter setter code is when reading it  If they all do getting and setting then you don t need to worry about what the function  does  when reading the code  There are a few other reasons to think about too    If source was protected  so accessible by subclasses  then code gets messy  who s changing the variables  When it s an object it then becomes hard when you need to refactor  whereas a method tends to make this step easier  If your getter setter methods aren t getting and setting  then describe them as something else    Always think whether your class is really a different thing or not  and that should help decide whether you need anything more

User · Answer

Of course   The whole idea of abstract classes is that they can contain some behaviour or data which you require all sub-classes to contain   Think of the simple example of WheeledVehicle - it should have a numWheels member variable   You want all sub classes to have this variable    Remember that abstract classes are a very useful feature when developing APIs  as they can ensure that people who extend your API won t break it

User · Answer

Sure   Why not  Abstract base classes are just a convenience to house behavior and data common to 2 or more classes in a single place for efficiency of storage and maintenance  Its an implementation detail  Take care however that you are not using an abstract base class where you should be using an interface  Refer to Interface vs Base class

User · Answer

I would have thought that something like this would be much better  since you re adding a variable  so why not restrict access and make it cleaner  Your getter setters should do what they say on the tin   public abstract class ExternalScript extends Script        private String source       public void setSource String file            source   file             public String getSource             return source            Bringing this back to the question  do you ever bother looking at where the getter setter code is when reading it  If they all do getting and setting then you don t need to worry about what the function  does  when reading the code  There are a few other reasons to think about too    If source was protected  so accessible by subclasses  then code gets messy  who s changing the variables  When it s an object it then becomes hard when you need to refactor  whereas a method tends to make this step easier  If your getter setter methods aren t getting and setting  then describe them as something else    Always think whether your class is really a different thing or not  and that should help decide whether you need anything more

User · Answer

Sure   Why not  Abstract base classes are just a convenience to house behavior and data common to 2 or more classes in a single place for efficiency of storage and maintenance  Its an implementation detail  Take care however that you are not using an abstract base class where you should be using an interface  Refer to Interface vs Base class

User · Answer

Sure   Why not  Abstract base classes are just a convenience to house behavior and data common to 2 or more classes in a single place for efficiency of storage and maintenance  Its an implementation detail  Take care however that you are not using an abstract base class where you should be using an interface  Refer to Interface vs Base class

User · Answer

I would have thought that something like this would be much better  since you re adding a variable  so why not restrict access and make it cleaner  Your getter setters should do what they say on the tin   public abstract class ExternalScript extends Script        private String source       public void setSource String file            source   file             public String getSource             return source            Bringing this back to the question  do you ever bother looking at where the getter setter code is when reading it  If they all do getting and setting then you don t need to worry about what the function  does  when reading the code  There are a few other reasons to think about too    If source was protected  so accessible by subclasses  then code gets messy  who s changing the variables  When it s an object it then becomes hard when you need to refactor  whereas a method tends to make this step easier  If your getter setter methods aren t getting and setting  then describe them as something else    Always think whether your class is really a different thing or not  and that should help decide whether you need anything more

User · Answer

Of course   The whole idea of abstract classes is that they can contain some behaviour or data which you require all sub-classes to contain   Think of the simple example of WheeledVehicle - it should have a numWheels member variable   You want all sub classes to have this variable    Remember that abstract classes are a very useful feature when developing APIs  as they can ensure that people who extend your API won t break it

User · Answer

I would have thought that something like this would be much better  since you re adding a variable  so why not restrict access and make it cleaner  Your getter setters should do what they say on the tin   public abstract class ExternalScript extends Script        private String source       public void setSource String file            source   file             public String getSource             return source            Bringing this back to the question  do you ever bother looking at where the getter setter code is when reading it  If they all do getting and setting then you don t need to worry about what the function  does  when reading the code  There are a few other reasons to think about too    If source was protected  so accessible by subclasses  then code gets messy  who s changing the variables  When it s an object it then becomes hard when you need to refactor  whereas a method tends to make this step easier  If your getter setter methods aren t getting and setting  then describe them as something else    Always think whether your class is really a different thing or not  and that should help decide whether you need anything more

User · Answer

Sure   Why not  Abstract base classes are just a convenience to house behavior and data common to 2 or more classes in a single place for efficiency of storage and maintenance  Its an implementation detail  Take care however that you are not using an abstract base class where you should be using an interface  Refer to Interface vs Base class

[java] Java - Abstract class to contain variables?

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