I'd like to extend ArrayList to add a few methods for a specific class whose instances would be held by the extended ArrayList. A simplified illustrative code sample is below.

This seems sensible to me, but I'm very new to Java and I see other questions which discourage extending ArrayList, for example Extending ArrayList and Creating new methods. I don't know enough Java to understand the objections.

In my prior attempt, I ending up creating a number of methods in ThingContainer that were essentially pass-throughs to ArrayList, so extending seemed easier.

Is there a better way to do what I'm trying to do? If so, how should it be implemented?

import java.util.*;

class Thing {
    public String name;
    public int amt;

    public Thing(String name, int amt) {
        this.name = name;
        this.amt = amt;
    }

    public String toString() {
        return String.format("%s: %d", name, amt);
    }

    public int getAmt() {
        return amt;
    }
}

class ThingContainer extends ArrayList<Thing> {
    public void report() {
        for(int i=0; i < size(); i++) {
            System.out.println(get(i));
        }
    }

    public int total() {
        int tot = 0;
        for(int i=0; i < size(); i++) {
            tot += ((Thing)get(i)).getAmt();
        }
        return tot;
    }

}

public class Tester {
    public static void main(String[] args) {
        ThingContainer blue = new ThingContainer();

        Thing a = new Thing("A", 2);
        Thing b = new Thing("B", 4);

        blue.add(a);
        blue.add(b);

        blue.report();
        System.out.println(blue.total());

        for (Thing tc: blue) {
            System.out.println(tc);
        }
    }
}
java arraylist extend
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