如何创建二维集合？

Question

有没有简单的方法来创建二维集合？

Answer 1

A two-dimensional collection is essentially having lists within a list. For example, to create a 2D ArrayList of strings, you would do something like this:

ArrayList<ArrayList<String>> stringList = new ArrayList<ArrayList<String>>();

To add a new row, you would simply add a new ArrayList:

stringList.add(new ArrayList<String>());

And here's how to add an element to the first row:

stringList.get(0).add("example string");

Answer 2

A 2d collection is a bit abstract... what do you mean? A double entry array is a 2d collection.

Why don't you use Multimaps from Guava library? https://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained , Those collections ads everything that the jdk is missing for dealing with 2d collections.