java - ArrayList 中不支持的异常

Question

我正在实现一个程序来从 2 个字符数组中删除重复项。我实现了这 2 个解决方案，解决方案 1 工作正常，但解决方案 2 给了我 UnSupportedOperationException。为什么会这样？错误位于行 al1.removeAll(al2);

public void getDiffernce(Character[] inp1, Character[] inp2){

    // SOLUTION 1:
    // **********************************************

    List<Character> list1 = new ArrayList<Character>(Arrays.asList(inp1));
    List<Character> list2 = new ArrayList<Character>(Arrays.asList(inp2));
    list1.removeAll(list2);

    System.out.println(list1);
    System.out.println("***************************************");


    // SOLUTION 2:

    Character a[] = {'f', 'x', 'l', 'b', 'y'};
    Character b[] = {'x', 'b','d'};

    List<Character> al1 = new ArrayList<Character>(); 
    List<Character> al2 = new ArrayList<Character>(); 
    al1 = (Arrays.asList(a)); System.out.println(al1);
    al2 = (Arrays.asList(b)); System.out.println(al2);  
    al1.removeAll(al2);         // error is here     
    System.out.println(al1);
}

Answer 1

来自asList(..)文档:

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 Collection.toArray(). The returned list is serializable and implements RandomAccess.

基本上是asList方法不会创建正常的可变 List<E>而是数组的包装器。 remove因此，操作在数组支持的列表上不可用。

尝试通过手动构建列表来构建列表:

List<Character> al1 = new ArrayList<Character>(Arrays.asList(a)) 

以便支持列表仅用于初始化真实的 ArrayList .