Inheritance. 

The text file. Working class dogs are now added to the text file
Working dogs have a trainer and therefore have an extra field

Butch#2#false
April#1#true
Shaka#2#true#Thabiso
Morgan#4#false
Ratty#9#false
Ricky#1#false#Khutso
Tut#2#true
Seal#1#false#Marge
===========================================================
The UI class that will call the methods in the manager class

/*
 * Super class: Dogs. Subclass: Working dogs
 * Read in from a text file
 */
package inheritance;

public class DogsUI {

    public static void main(String[] args) {
        DogManager dm = new DogManager();
        String text = dm.displayAll();
        System.out.println("Hello Dogs");
        System.out.println(text);
    }
}
===============================================================
The constructor method will read in the text file and 
instantiate Dog objects and Working Dog objects.
Note however that we only use one array, and that array if of
the parent class ie Dog (not Working Dog)

/*
 * Dog Manager with methods to create object arrays
 */
package inheritance;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DogManager {
    // global variables including arrays
    // The array is of the parent class ie only one array type
    private Dogs[] dogArray = new Dogs[20];
    private int size = 0;
    
    DogManager() {
        try {
            Scanner scFile = new Scanner(new File("dogs.txt"));
            
            while(scFile.hasNext()) {
                String line = scFile.nextLine();
                Scanner scLine = new Scanner(line).useDelimiter("#");
                String name = scLine.next();
                String ageSt = scLine.next();
                int age = Integer.parseInt(ageSt);
                String pedigreeSt = scLine.next();
                boolean pedigree = Boolean.parseBoolean(pedigreeSt);
                
                //Separate working dogs from dogs
                // Each class has a different constructor method
                if(scLine.hasNext()) {
                    String trainer = scLine.next();
                    dogArray[size] = new WorkingDog (name, age, pedigree,trainer);
                }
                else {
                    dogArray[size] = new Dogs (name, age, pedigree);
                }
                
                size = size + 1;
            } // end while
            System.out.println("File Found");
        } catch (FileNotFoundException ex) {
            System.out.println("Error. File not found.");
            Logger.getLogger(DogManager.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    
    public String displayAll() {
        String s = "";
        for(int i = 0; i < size; i++) {
            s = s + dogArray[i] + "\n";
        } // end for
        return s;
    }
}
==============================================================================
The Dog class - the super class. The dog class constructor must match the
working dog constructor ie the first three fields must match each other

/*
 * Super class: Dogs. Subclass: Working dogs
 */
package inheritance;

public class Dogs {
    String name = null;
    int age = 0;
    boolean pedigree = false;
    
    Dogs(String n, int a, boolean p) {
        name = n;
        age = a;
        pedigree = p; 
    }
    
public String toString() {
    
    return name + "\t" + age + "\t" + pedigree;
}
}
===============================================================================
/*
 * Extends the dog class
 */
package inheritance;

public class WorkingDog extends Dogs{
    // Working dog has an additional field
    String trainer = "Nil";
    
    // Sub-class constructor uses the super-class constructor, just adding the
    // extra field
	
    WorkingDog(String n, int a, boolean p, String t) {
        super(n,a,p);
        trainer = t;
    } // end constructor

public String toString() {
    // returns Dog toString with the extra field
    return super.toString() + "\t" + trainer;
}
}
================================================================================

OUTPUT

run:
Butch	2	false
April	1	true
Shaka	2	true	Thabiso
Morgan	4	false
Ratty	9	false
Ricky	1	false	Khutso
Tut	2	true
Seal	1	false	Marge

BUILD SUCCESSFUL (total time: 0 seconds)
=================================================================================