Java 尝试添加另一个列表时 List.addAll 抛出 UnsupportedOperationException
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List.addAll throwing UnsupportedOperationException when trying to add another list
提问by Batty
List.addAll throwing UnsupportedOperationExceptionwhen trying to add another list.
List.addAllUnsupportedOperationException在尝试添加另一个列表时抛出。
List<String> supportedTypes = Arrays.asList("6500", "7600"};
and in loop I am doing,
在循环中我正在做，
supportedTypes.addAll(Arrays.asList(supportTypes.split(","))); //line 2
reading supportTypesfrom a file.
从文件中读取supportTypes。
But line 2 throws a UnsupportedOperationException, but I am not able to determine why?
但是第 2 行抛出了一个UnsupportedOperationException，但我无法确定为什么？
I am adding another list to a list, then why this operation is unsupported?
我正在向列表中添加另一个列表，那么为什么不支持此操作？
采纳答案by Eran
Arrays.asListreturns a fixed sized list backed by an array, and you can't add elements to it.
Arrays.asList返回由数组支持的固定大小的列表，您不能向其中添加元素。
You can create a modifiable list to make addAllwork :
您可以创建一个可修改的列表来addAll工作：
List<String> supportedTypes = new ArrayList<String>(Arrays.asList("6500", "7600", "8700"));
List<String> supportedTypes = new ArrayList<String>(Arrays.asList("6500", "7600", "8700"));
回答by Jean Logeart
Arrays.asList returns a fixed-size list.
Arrays.asList 返回一个固定大小的列表。
If you to want be able to add elements to the list, do:
如果您希望能够向列表中添加元素，请执行以下操作：
List<String> supportedTypes = new ArrayList<>(Arrays.asList("6500", "7600"});
supportedTypes.addAll(Arrays.asList(supportTypes.split(",")));
回答by bsiamionau
Problem is that Arrays.asListmethod returns instance of java.util.Arrays.ArrayListwhich doesn't support add/remove operations on elements. It's not surprizing that addAllmethod throws exception because add method for java.util.Arrays.ArrayListis defined as:
问题是该Arrays.asList方法返回java.util.Arrays.ArrayList 的实例，它不支持对元素的添加/删除操作。addAll方法抛出异常并不奇怪，因为 add 方法java.util.Arrays.ArrayList定义为：
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
Related question:
相关问题：
Arrays.asList() Confusing source code
From the documentation:
从文档：
Arrays.asListreturns a fixed-size list backed by the specified array.
Arrays.asList返回由指定数组支持的固定大小列表。
回答by Suragch
This error also happens when the list is initialized with Collections.emptyList(), which is immutable:
当列表用 初始化时也会发生此错误Collections.emptyList()，这是不可变的：
List<String> myList = Collections.emptyList();
Instead, initialize it with a mutable list. For example
相反，用可变列表初始化它。例如
List<String> myList = new ArrayList<>();
回答by CoolMind
In my case this exception occured when I called adapter.addAll(items), where adapterwas a custom ArrayAdapter. This CustomAdapter had a parameter of type Arrayinstead of ArrayList.
在我的情况下，这个异常发生在我调用时adapter.addAll(items)，adapter自定义ArrayAdapter. 这个 CustomAdapter 有一个 typeArray而不是 的参数ArrayList。
