Question

Is there a nice way in Java to read a parameter from an object in a list? For example I often want to get all ids in my objects that are part of a list. The code I usually write for this is as below.

List<Integer> ids = new ArrayList<Integer>();
for (MyObject myObj : myObjs){
    ids.add(myObj.getId());
}

Is there any other way of doing this or any other pattern? Or am I just waiting for (proper) closures to appear in java. All I want is a one-line to return a list of all the values of one parameter of a list.

Thanks

Answer 1

Guava Lists.transform:

final List<Integer> ids = Lists.transform(myObjs, new Function<MyObject, Long>() {
    public Long apply(final MyObject input) {
        return input.getId();
    }
});

EDIT: you can also use a custom ToId class implementing Function<F, T>