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Using methods inherited from the base class Object
Extending Classes and More example from a Well House Consultants training course
More on Extending Classes and More [link]

This example is described in the following article(s):
   • What is a universal superclass? Java / Perl / Python / Other OO languages - [link]

Source code: Lunch.java Module: J710
public class Lunch {

/* Using methods inherited from the base class Object

Every Java object inherits from the base class Object - whether it's through
another intermediate class or directly. If you don't declare that a class
extends anthing, it defaults to extending Object.

The Object base class provides methods such as:

toString - Converts an obect to a string (default result - "type@address")
equal - Returns true if both pint to one and the same object
clone - Returns a duplicate object (not a duplicated pointer)
finalize - tidies up when the garbage collector releases memory (descructor)
getClass - returns a class object to tell you the object type
hashCode - returns a hash code value for the object

There are also methods associated with threading -
wait ... notify ... notifyAll

Methods such as toString and equal are designed for you to override in your
own classes, providing apporpriate string representions for your objects when
you output them without calling a specific method, and a comparator which lets
you identify if two objects or a particular type are the same.


        public String Descriptor;
        private int portions;
        int cals; // No "p" word so "package" ;-)

        protected Lunch (String Descriptor, int portions, int cals) {
                this.Descriptor = Descriptor;
                this.portions = portions;
                this.cals = cals;

        public String toString() {
                String About = "Type = " + "Lunch" +
                                "; Product = " + this.Descriptor +
                                "; Portions = " + this.portions +
                return About;

        public boolean equals(Lunch that) {
                return (this.cals == that.cals);

        public static void main ( String [] args) {

                Lunch [] Item = new Lunch[6];

                Item[0] = new Lunch("Chilli Con Carne",4,175);
                Item[1] = new Lunch("Roast Potatoes",5,160);
                Item[2] = new Lunch("Chicken Drumsticks",3,175);
                Item[3] = new Lunch("Fresh Fruit Salad",4,120);
                Item[4] = new Lunch("Roombikkies",35,120);
                Item[5] = new Lunch("Coffee",66,10);

                for (int k=0; k<Item.length; k++) {

                // To test "equals" - anything like anything else?

                for (int j=0; j<Item.length-1; j++) {
                        Lunch Maybe = Item[j];
                        for (int k=j+1; k<Item.length; k++) {
                                if (Maybe.equals(Item[k])) {
                                        System.out.println (Maybe +
                                                " - could substitute " + Item[k]);

/* Sample output:

wizard:jn10 graham$ java Lunch
Type = Lunch; Product = Chilli Con Carne; Portions = 4;
Type = Lunch; Product = Roast Potatoes; Portions = 5;
Type = Lunch; Product = Chicken Drumsticks; Portions = 3;
Type = Lunch; Product = Fresh Fruit Salad; Portions = 4;
Type = Lunch; Product = Roombikkies; Portions = 35;
Type = Lunch; Product = Coffee; Portions = 66;
Type = Lunch; Product = Chilli Con Carne; Portions = 4; - could substitute
                        Type = Lunch; Product = Chicken Drumsticks; Portions = 3;
Type = Lunch; Product = Fresh Fruit Salad; Portions = 4; - could substitute
                        Type = Lunch; Product = Roombikkies; Portions = 35;
wizard:jn10 graham$


Learn about this subject
This module and example are covered on the following public courses:
 * Learning to Program in Java
 * Java Bootcamp
 * Java Programming for the Web
Also available on on site courses for larger groups

Books covering this topic
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Other Examples
This example comes from our "Extending Classes and More" training module. You'll find a description of the topic and some other closely related examples on the "Extending Classes and More" module index page.

Full description of the source code
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Other resources
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