instantiating an abstract class

[sugard]

I need to access some data which is in an abstract class. Though you cannot inistialise an abstract class.

The task to do is gathering data from a textfile where data is in this format..
P Charles Galea 134

Where my class needs to check if the first letter is a P it do the stuff in the professors class and if it is an S it do the stuff in the Students class. The professor and student class inherits the SchoolMember abstract class which is follows.

public abstract class SchoolMember {
 
    //These are the attributes for a SchoolMember class
 
    String typeOfMember;
    String name;
    String surname;
    Integer score;
 
    public abstract boolean outstanding(String s);
 
}

and this class

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
 
/* This class is going to be used to parse the file
 * and gets data from this file to check if the student or the 
 * professor is outstanding or not
*/
public class FileParser {
 
    public SchoolMember[] convert(String s) {
 
    FileReader f = null;
    BufferedReader buf = null;
 
    try {
        f = new FileReader(s);
        buf = new BufferedReader(f);
 
        String line = buf.readLine();
 
        while (line != null) {
 
            String[] datum = line.split(" ");
 
        //    Student stud = new Student();
        //    Professor prof = new Professor();
 
          //  if (SchoolMember.typeOfMember.equals("S") ) {
 
            //    stud.outstanding(s);
 
            }
 
         //   else if (SchoolMember.typeOfMember.equals("P")) {
 
           //     prof.outstanding(s);
    //        }
 
        }    
    }
            catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
 
                try {
                    if (buf != null) {
                        buf.close();
                    }
                    buf.close();
                    f.close();
                } catch (IOException e) {
                    // just ignore
                }
            }
 
            return null;
 
    }
}

Can please some1 help me correct the commemted part..? where i need to check if the first item in the textfile is a 'p' or an 's' and according to what it is do the specified method?

thank you

[r035198x]

Your thread title does not make any sense. You cannot instantiate an abstract class. The problem discussed has nothing to do with abstract classes. If you want to know how to read files you can read this article

[Nepomuk]

I need to access some data which is in an abstract class. Though you cannot inistialise an abstract class.

The task to do is gathering data from a textfile where data is in this format..
P Charles Galea 134

Where my class needs to check if the first letter is a P it do the stuff in the professors class and if it is an S it do the stuff in the Students class. The professor and student class inherits the SchoolMember abstract class which is follows.

public abstract class SchoolMember {
 
    //These are the attributes for a SchoolMember class
 
    String typeOfMember;
    String name;
    String surname;
    Integer score;
 
    public abstract boolean outstanding(String s);
 
}

and this class

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
 
/* This class is going to be used to parse the file
 * and gets data from this file to check if the student or the 
 * professor is outstanding or not
*/
public class FileParser {
 
    public SchoolMember[] convert(String s) {
 
    FileReader f = null;
    BufferedReader buf = null;
 
    try {
        f = new FileReader(s);
        buf = new BufferedReader(f);
 
        String line = buf.readLine();
 
        while (line != null) {
 
            String[] datum = line.split(" ");
 
        //    Student stud = new Student();
        //    Professor prof = new Professor();
 
          //  if (SchoolMember.typeOfMember.equals("S") ) {
 
            //    stud.outstanding(s);
 
            }
 
         //   else if (SchoolMember.typeOfMember.equals("P")) {
 
           //     prof.outstanding(s);
    //        }
 
        }    
    }
            catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
 
                try {
                    if (buf != null) {
                        buf.close();
                    }
                    buf.close();
                    f.close();
                } catch (IOException e) {
                    // just ignore
                }
            }
 
            return null;
 
    }
}

Can please some1 help me correct the commemted part..? where i need to check if the first item in the textfile is a 'p' or an 's' and according to what it is do the specified method?

thank you

OK, you have an array of Strings called datum and the first Element of this array should be either a "P" or an "S", correct? So just check, which of both it is.

Next, the commented part seems to create both a Student and a Professor for each line - don't do that, it's a waste of space. Create one of both, depending on the earlier test.

Also, you don't seem to read that line more than once. Either add a

line = buf.readLine();
 

at the end of the while-loop or have the while loop doing it itself with

while ((String line = buf.readLine()) != null)
// ...
 

Does that help?

Greetings,
Nepomuk

[JosAH]

I'd say: a static factory method in the abstract base class.

kind regards,

Jos

[sugard]

yes it helped thanks! but my problem is still how am I going to combine them both the student and the professor so that i will use only 1?
As i cant use the abstract class. How am i going to check if the first element is a 'P' or an 'S'? which class am i going to instantiate?

I dont know if u can understand what i am saying.

[r035198x]

I'd say: a static factory method in the abstract base class.

kind regards,

Jos

Thanks for the correction.
Today is national no defenestration day so I get away with that.

[JosAH]

yes it helped thanks! but my problem is still how am I going to combine them both the student and the professor so that i will use only 1?
As i cant use the abstract class. How am i going to check if the first element is a 'P' or an 'S'? which class am i going to instantiate?

I dont know if u can understand what i am saying.

Read my reply #4: the static method can determine which of the two to instantiate.
Pass that method the line you just have read and let it figure out the details.

kind regards,

Jos

[r035198x]

yes it helped thanks! but my problem is still how am I going to combine them both the student and the professor so that i will use only 1?
As i cant use the abstract class. How am i going to check if the first element is a 'P' or an 'S'? which class am i going to instantiate?

I dont know if u can understand what i am saying.

You can do

SchoolMember member;
if(element.equals("P")) {
   member = new Professor();
}
else if (element.equals("S")) {
    member = new Student();
}

Edit: But Jos' approach is much better of course.

[JosAH]

You can do

SchoolMember member;
if(element.equals("P")) {
   member = new Professor();
}
else if (element.equals("S")) {
    member = new Student();
}

Edit: But Jos' approach is much better of course.

Mais naturellement mon ami ;-) btw, the method would be similar but it's the
place where that method belongs; the abstract base class is the place where
the method should be and figure out what exactly to instantiate; it's the factory
method pattern thingy. If more and more different SchoolMembers see the light,
that little pattern should be abandoned asap.

kind regards,

Jos

[sugard]

Thanks very much for your help.
I deceided to do the last one since it is easier for me.

String[] datum = line.split(" ");
 
            SchoolMember member;
 
            if (typeOMember.equals("S") ) {
                member = new Student();      
            }
 
            else if (typeOfMember.equals("S")) {
 
                member = new Professor();
            }
 

I' ve altered the code to that. But I am still encountering a difficulty in this part the typeOfMember.equals since there is an error saying that the type typeOfMember cannot be solved.

[r035198x]

Thanks very much for your help.
I deceided to do the last one since it is easier for me.

String[] datum = line.split(" ");
 
            SchoolMember member;
 
            if (typeOMember.equals("S") ) {
                member = new Student();      
            }
 
            else if (typeOfMember.equals("S")) {
 
                member = new Professor();
            }
 

I' ve altered the code to that. But I am still encountering a difficulty in this part the typeOfMember.equals since there is an error saying that the type typeOfMember cannot be solved.

A basic rule of Java is that you have to declare variables before you can use them.
P.S The other approach is not difficult, you simply move that code to the abstract class in a method called, say, getInstance.

[JosAH]

Thanks very much for your help.
I deceided to do the last one since it is easier for me.

String[] datum = line.split(" ");
 
            SchoolMember member;
 
            if (typeOMember.equals("S") ) {
                member = new Student();      
            }
 
            else if (typeOfMember.equals("S")) {
 
                member = new Professor();
            }
 

I' ve altered the code to that. But I am still encountering a difficulty in this part the typeOfMember.equals since there is an error saying that the type typeOfMember cannot be solved.

Where does that typeOfMember come from? Did you define a String like that?
You're splitting a line; the line parts are stored in the 'datum' String array; that's
where you should look for an "S" or "P" not in a made up 'typeOfMember' thing.

Please try to understand what those code snippets are all about before you just
blindly copy and paste them. btw that piece of code could easily be placed in
a static method in that abstract base class in which case you have defined your
factory method; that's how it's called.

kind regards,

typofKindaSortofJos

[sugard]

typeOfMember is a variable in the SchoolMember class.

[r035198x]

typeOfMember is a variable in the SchoolMember class.

So you now see why that code belongs in that abstract class?

[JosAH]

typeOfMember is a variable in the SchoolMember class.

Sure and where did you store that piece of code? In your FileParser?

kind regards,

Jos

[sugard]

yes i can understand better now what you are saying. But do i need to remove the whole fileparser class and place it in the abstract class? or just place that part only in the abstract class?

[r035198x]

yes i can understand better now what you are saying. But do i need to remove the whole fileparser class and place it in the abstract class? or just place that part only in the abstract class?

Now, let's not play a jigsaw puzzle game with the code here. Why does a SchoolMember need to have a FileParser?

[JosAH]

yes i can understand better now what you are saying. But do i need to remove the whole fileparser class and place it in the abstract class? or just place that part only in the abstract class?

You did read and tried to understand my reply #12 didn't you?

kind regards,

Jos

[sugard]

yes i read all the posts and I understood the code but i am still not understanding what i need to do. If i need to take all the code or not.

[JosAH]

yes i read all the posts and I understood the code but i am still not understanding what i need to do. If i need to take all the code or not.

Ok, this is a giveaway then:

public class Student extends SchoolMember { ... }
public class Professor extends SchoolMember { ... }
...
public abstract class SchoolMember {
 
   public static SchoolMember getInstance(String description) {
      if (<blahblahbah>) return new Professor( ... );
      return new Student( ... );
   }
}
 

Now that's what a simple factory method is all about. Compare this with, say,
the Calendar class where they do something similar.

kind regards,

Jos