今天又跳一坑, sample code:
List<Integer> list = Arrays.asList(1, 2, 3);
list.clear(); // throws java.lang.UnsupportedOperationException
Arrays.asList()返回的是一個固定長度的List,不支援add() remove() clear()等操作
/**
* Returns a fixed-size list backed by the specified array. (Changes to
* the returned list "write through" to the array.) This method acts
* as bridge between array-based and collection-based APIs, in
* combination with {@link Collection#toArray}. The returned list is
* serializable and implements {@link RandomAccess}.
*
* <p>This method also provides a convenient way to create a fixed-size
* list initialized to contain several elements:
* <pre>
* List<String> stooges = Arrays.asList("Larry", "Moe", "Curly");
* </pre>
*
* @param a the array by which the list will be backed
* @return a list view of the specified array
*/
@SafeVarargs
public static <T> List<T> asList(T... a) {
return new ArrayList<>(a);
}
注意上面那個ArrayList是Arrays的內部類,同樣extends了AbstractList但沒有實現add()那些方法,所以就蛋疼了