How To implement Compare to method for custom object

Question

In java i have an arrayList of my own(implemented) i have a sort method so i need 'compareTo' method thats why i implemented Comparable and made the class abstract. But if i use arraylist from main i have to implement compare to method .But I cant understand how i can implement this.( I have a restriction, for example if i have a arraylist of 'order' class i cant implement comparable in order class)

Arraylist

public abstract class ArrayList<T>  implements  Comparable

inside sort function

    Comparable left=(Comparable)L[i];
    Comparable right=(Comparable)R[j];
    for(int k=start;k<=end;k++)
    {
        if(left.compareTo(right)<=0)
        {
            array[k]=L[i];
            i++;
            left=(Comparable)L[i];

        }

From main

ArrayList<Order> order = new ArrayList<Order>() {
        @Override
        public int compareTo(Object o) {
            if(this)// but this main is not order class this is arraylist class
            return 0;
        }
    };

Check what @Loic M. said. Basically when you implement Comparable interface that means you want that particular object to be comparable with other object that's why you have to implement compareTo(Object o) method. What you really want is to compare elements so you should implement Comparable interface on the elements in the List — Michal
– Michal, Commented May 11, 2016 at 15:04

Community · Accepted Answer · 2017-05-23 12:16:04Z

1

Why does your ArrayList implements Comparable? Do you want to compare 2 lists? If you want to compare or order the elements of the list, the elements should be Comparable, but not the list itself.

You can also have a look to the following issue: How to use Comparator in Java to sort You will then have to implement a Comparator for your class Order (not the interface Comparable)

edited May 23, 2017 at 12:16

CommunityBot

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answered May 11, 2016 at 14:51

Loic Mouchard

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1 Comment

Shuvo Over a year ago

OOps. i have made a great a mistake.Thanks a lot

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