Java: ArrayList initializing (difference between 2 code lines)

Question

i hope my question won't sound stupid but i'd like to know what's the difference between these two lines:

(Assuming I made a class named Cow..)

ArrayList<Cow> c1 = new ArrayList<Cow>();

ArrayList<Cow> c2 = new ArrayList();

Thanks in advance for ur explanation.

Try compiling the code with the javac -Xlint option and see what the compiler has to say about it. — Andy
– Andy, Commented Feb 29, 2012 at 15:10
You will get these annoying warnings in eclipse (for example) if you use the second option : ) — Jerome
– Jerome, Commented Feb 29, 2012 at 15:12
Ye something came up, even by using javac without the 2nd attribute u just gave it notes something, well anyway i dont care much about the tech details i just like to know if the list itself is different in some way.. — Popokoko
– Popokoko, Commented Feb 29, 2012 at 15:15

ruakh · Accepted Answer · 2012-02-29 15:09:14Z

7

Currently, there is essentially no difference, due to type erasure. The first form is preferred; the second form uses a raw type, and is only supported for backward-compatibility with older versions of Java. A good compiler will give you warnings if you use it.

As the Java Language Specification, Third Edition, §4.8 explains:

The use of raw types is allowed only as a concession to compatibility of legacy code. The use of raw types in code written after the introduction of genericity into the Java programming language is strongly discouraged. It is possible that future versions of the Java programming language will disallow the use of raw types.

(emphasis in original).

answered Feb 29, 2012 at 15:09

ruakh

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1 Comment

Popokoko Over a year ago

hm got it! so as u said the list itself is basiclly the same, well explained mate :)

J.A.I.L. · Accepted Answer · 2012-02-29 15:36:54Z

1

As ruakh has just pointed out, the first one is preferred, and actually there won't be any difference duriong execution.

Explained in simpler words: In both lines you are declaring a list of Cow In the first line you instantiate it with a list of Cow. In the second one you instantiate it with a list of Object (and Cow is a subclass of Object).

It would be even better to declare it as the list interface List.

List<Cow> listOfCows = new ArrayList<Cow>();

answered Feb 29, 2012 at 15:36

J.A.I.L.

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