indexOf() using ArrayList in java

Question

I've a class A which is as follows:

A{
     String name;
     ArrayList<Bike> firstArray;
     ArrayList<Cycle> secondArray;
     // it's constructors and related methods are down lines.
 }

and I have two instances of it named a_Obj and b_obj. I compare only the variable ,name inside object a_Obj with b_Obj using indexOf.

My question is how to call indexOf in this case and in other words how to tell the compiler that I just want to compare name of two objects regardless of ArrayLists declared inside the class A.

jpell · Accepted Answer · 2020-03-01 18:57:45Z

1

you can override equals() in your class

answered Mar 1, 2020 at 18:57

jpell

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Comments

Arvind Kumar Avinash · Accepted Answer · 2020-06-25 10:55:43Z

0

Given below is how indexOf has been implemented by default:

public int indexOf(Object o) {
    ListIterator<E> it = listIterator();
    if (o==null) {
        while (it.hasNext())
            if (it.next()==null)
                return it.previousIndex();
    } else {
        while (it.hasNext())
            if (o.equals(it.next()))
                return it.previousIndex();
    }
    return -1;
}

By overriding the equals method in A to consider just the equality of name, you can make it happen.

Given below is the definition generated by Eclipse IDE:

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    A other = (A) obj;
    if (name == null) {
        if (other.name != null)
            return false;
    } else if (!name.equals(other.name))
        return false;
    return true;
}

A shorter version for the same can be as follows:

@Override
public boolean equals(Object obj) {
    if (obj == null)
        return false;
    A other = (A) obj;
    return Objects.equals(name, other.name);
}

edited Jun 25, 2020 at 10:55

answered Mar 1, 2020 at 19:04

Arvind Kumar Avinash

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2 Comments

WJS Over a year ago

return name.equals(other.name);

Arvind Kumar Avinash Over a year ago

@WJS - I do not approve your suggested solution as it will throw NullPointerException when name is null.

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