Question

I want to add multiple BigInteger values to an ArrayList. All I have found is examples that repeatedly add single values, each expressed on their own line of code. I’m looking for something like

ArrayList<BigInteger> array = {bigInt1, bigInt2, bigInt3};

and instead it’s:

ArrayList<BigInteger> array = new ArrayList<BigInteger>();
array.add(bigInt1);
array.add(bigInt2);
array.add(bigInt3);

Can it be done, without adding one element/line or using a for loop?

Answer 1

I’m not really sure what you’re after. You have four alternatives:

1. Add items individually

Instantiate a concrete List type and then call add() for each item:

List<BigInteger> list = new ArrayList<BigInteger>();
list.add(new BigInteger("12345"));
list.add(new BigInteger("23456"));

2. Subclass a concrete List type (double brace initialization)

Some might suggest double brace initialization like this:

List<BigInteger> list = new ArrayList<BigInteger>() {{
  add(new BigInteger("12345"));
  add(new BigInteger("23456"));
}};

I recommend not doing this. What you’re actually doing here is subclassing ArrayList, which (imho) is not a good idea. That sort of thing can break Comparators, equals() methods and so on.

3. Using Arrays.asList()

Another approach:

List<BigInteger> list = new ArrayList<BigInteger>(Arrays.asList(
  new BigInteger("12345"),
  new BigInteger("23456")
));

or, if you don’t need an ArrayList, simply as:

List<BigInteger> list = Arrays.asList(
  new BigInteger("12345"),
  new BigInteger("23456")
);

I prefer one of the above two methods.

4. Collection literals (Java 7+)

Assuming Collection literals go ahead in Java 7, you will be able to do this:

List<BigInteger> list = [new BigInteger("12345"), new BigInteger("23456")];

As it currently stands, I don’t believe this feature has been confirmed yet.

That’s it. Those are your choices. Pick one.