Can I get a List from an object, add a String to it, and set it back to the object in one line?

Question

I was wondering if one can get a List from an object, add an item to it, and set the List to the object in one line.

I would normally do it this way:

List<String> tempList = someObject.getList();
tempList.add("some string value");
someObject.setList(tempList);

What I tried doing was this:

someObject.setList(someObject.getList().add("some string value"));

But then I realized that the method add() would return a boolean while the method setList() takes a List<String>

Any ideas?

score 5 · Answer 1 · answered Dec 31 '16 at 16:02

5

As far as I know there is no nice way to do this in one line.

If you need to do this a lot, you could modify the class of someObject to have an addItem method to do this directly.

Alternatively, if you cannot modify the class, you could write a method for adding to a list and returning the list:

static <E> List<E> add(List<E> list, E extra) {
    list.add(extra);
    return list; 
}

answered Dec 31 '16 at 16:02

Paul Boddington

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+1 for a simple solution. I knew I could do this, but wanted to know if I could do it directly without creating new methods. – yogur Jan 03 '17 at 14:56

score 4 · Accepted Answer · answered Dec 31 '16 at 16:38

4

Assuming you aren't returning a copy in getList it should be the same reference, so you can say

someObject.getList().add("some string value");

And you should not need to setList back, because there is only one List.

answered Dec 31 '16 at 16:38

Elliott Frisch

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May you offer more explanation on how it works. I was not aware that we could manipulate objects by reference in Java. – yogur Jan 03 '17 at 14:55
1

[Is Java “pass-by-reference” or “pass-by-value”?](http://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) Java is always pass by value, but the value of objects (reference types) **is-a** reference. – Elliott Frisch Jan 03 '17 at 15:48

score 2 · Answer 3 · answered Dec 31 '16 at 17:40

Just because you can do something in one statement, doesn't mean you should!

But it's certainly possible if you don't mind abusing the streams a little bit:

    Stream.of(someObject.getList())
            .map(list -> new Pair<>(list.add(new Object()), list))
            .forEach(pair -> someObject.setList(pair.getValue()));

Of course the real answer is, if you want to do things like this in one line you should simply write a method with as many lines as needed for clarity, then call it (in one line).

Can I get a List from an object, add a String to it, and set it back to the object in one line?

3 Answers3