Java - ArrayList d'initialisation équivalente à l'initialisation du tableau - Stack Overflow

I am aware that you can initialize an array during instantiation as follows:

String[] names = new String[] {"Ryan", "Julie", "Bob"};

Is there a way to do the same thing with an ArrayList? Or must I add the contents individually with array.add()?

Arrays.asList can help here:

new ArrayList<Integer>(Arrays.asList(1,2,3,5,8,13,21));

Yes.

new ArrayList<String>(){{
   add("A");
   add("B");
}}

What this is actually doing is creating a class derived from ArrayList<String> (the outer set of braces do this) and then declare a static initialiser (the inner set of braces). This is actually an inner class of the containing class, and so it'll have an implicit this pointer. Not a problem unless you want to serialise it.

I understand that Java 7 will provide additional language constructs to do precisely what you want.

Here is the closest you can get:

ArrayList<String> list = new ArrayList(Arrays.asList("Ryan", "Julie", "Bob"));

You can go even simpler with:

List<String> list = Arrays.asList("Ryan", "Julie", "Bob")

Looking at the source for Arrays.asList, it constructs an ArrayList, but by default is cast to List. So you could do this (but not reliably for new JDKs):

ArrayList<String> list = (ArrayList<String>)Arrays.asList("Ryan", "Julie", "Bob")

Arrays.asList("Ryan", "Julie", "Bob");

Well, in Java there's no literal syntax for lists, so you have to do .add().

If you have a lot of elements, it's a bit verbose, but you could either:

1. use Groovy or something like that


2. use Arrays.asList(array)

2 would look something like:

String[] elements = new String[] {"Ryan", "Julie", "Bob"};
List list = new ArrayList(Arrays.asList(elements));

This results in some unnecessary object creation though.

This is how it is done using the fluent interface of the op4j Java library (1.1. was released Dec '10) :-

List<String> names = Op.onListFor("Ryan", "Julie", "Bob").get();

It's a very cool library that saves you a tonne of time.

I am aware that you can initialize an array during instantiation as follows:

String[] names = new String[] {"Ryan", "Julie", "Bob"};

Is there a way to do the same thing with an ArrayList? Or must I add the contents individually with array.add()?

Arrays.asList can help here:

new ArrayList<Integer>(Arrays.asList(1,2,3,5,8,13,21));

Yes.

new ArrayList<String>(){{
   add("A");
   add("B");
}}

What this is actually doing is creating a class derived from ArrayList<String> (the outer set of braces do this) and then declare a static initialiser (the inner set of braces). This is actually an inner class of the containing class, and so it'll have an implicit this pointer. Not a problem unless you want to serialise it.

I understand that Java 7 will provide additional language constructs to do precisely what you want.

Here is the closest you can get:

ArrayList<String> list = new ArrayList(Arrays.asList("Ryan", "Julie", "Bob"));

You can go even simpler with:

List<String> list = Arrays.asList("Ryan", "Julie", "Bob")

Looking at the source for Arrays.asList, it constructs an ArrayList, but by default is cast to List. So you could do this (but not reliably for new JDKs):

ArrayList<String> list = (ArrayList<String>)Arrays.asList("Ryan", "Julie", "Bob")

Arrays.asList("Ryan", "Julie", "Bob");

Well, in Java there's no literal syntax for lists, so you have to do .add().

If you have a lot of elements, it's a bit verbose, but you could either:

1. use Groovy or something like that


2. use Arrays.asList(array)

2 would look something like:

String[] elements = new String[] {"Ryan", "Julie", "Bob"};
List list = new ArrayList(Arrays.asList(elements));

This results in some unnecessary object creation though.

This is how it is done using the fluent interface of the op4j Java library (1.1. was released Dec '10) :-

List<String> names = Op.onListFor("Ryan", "Julie", "Bob").get();

It's a very cool library that saves you a tonne of time.

Source