Return element's index in ArrayList

Question

I have an ArrayList of say, this object:

class Object() {
    String name;
    double price;
    int id;
}

I want to find the index of the ArrayList that contains the element where the name field is equal to a given string. For example:

public int findIndex(ArrayList<Object> list, String name) {
    for(Object o : list) {
        if (o.getName().equals(name) {
            //return index
        }
    }
}

What's a good way to return the index?

It's just an example, consider the class being called anything — John, May 20 '20 at 07:39
Is it possible that more than one object may have the same value you're searching for? If so, do you want to return an array of indexes or only the first one? — CrystalSpider, May 20 '20 at 07:40

score 3 · Answer 1 · answered May 20 '20 at 07:41

You can iterate the list with an indexed-for-loop:

for(int i = 0; i < list.size(); i++) { 
    if (list.get(i).getName().equals(name)) { 
        return i; 
    } 
} 
return -1;

Or simply use a counting variable when you want to use the for-each-loop:

int i = 0;
for(Object o : list) {
    if (o.getName().equals(name)) {
        return i;
    }
    i++;
}
return -1;

Or using Java-8 streams:

return IntStream.range(0, list.size())
    .filter(i -> list.get(i).getName().equals(name))
    .findFirst()
    .orElse(-1);

You see that I returned -1 when nothing was found. This is a common concept used throughout the java language.

score -2 · Answer 2 · answered May 20 '20 at 07:42

I think you can just do:

public int findIndex(ArrayList<Object> list, String name) {
    for(Object o : list) {
        if (o.getName().equals(name) {
            return list.indexOf(o);
        }
    }
    return -1;
}

(-1 is returned if nothing was found).

2 Answers2