pcwiki的部落格

http://stackoverflow.com/questions/689370/java-collections-copy-list-i-dont-understand

若想要複製 collections
那要用下列方法:

List<String> b =newArrayList<String>(a);

creates a shallow copy of a within b. All elements will exist within b in the exact same order that they were within a (assuming it had an order).

不能用以下方法，會失敗因為雖然給了a.size，但實際上b的size還是0，不同size不能做copy。

// note: instantiating with a.size() gives `b` enough capacity to hold everythingList<String> b =newArrayList<String>(a.size());Collections.copy(b, a);