java - 为什么在Java中按比较器排序时collections.sort会抛出不受支持的操作异常? [英] Why does collections.sort throw unsupported operation exception while sorting by comparator in Java?

问题描述

以下是我用于按预定义顺序对列表进行排序的代码.itemsSorted 列表中提到了定义的顺序.

Following is my code used to sort a list with predefined order. Defined order is mentioned in itemsSorted list.

final List<String> itemsSorted = myMethod.getSortedItems();

List<String> plainItemList = myMethod2.getAllItems();

final Comparator<String> comparator = new Comparator<String>() {        

    public int compare(String str1, String str2) {
        return orderOf(str1) - orderOf(str2);
    }

    private int orderOf(String name) {          
        return ((itemsSorted)).indexOf(name);
    }
 };
 Collections.sort(plainItemList, comparator);
 return plainItemList;

上面的代码抛出

Caused by: java.lang.UnsupportedOperationException
    at java.util.Collections$UnmodifiableList$1.set(Collections.java:1244)
    at java.util.Collections.sort(Collections.java:221)

我不确定为什么该列表不可修改.请帮我解决这个问题.

I'm not sure why the list is unmodifiable. Please help me on this.

推荐答案

该列表不可修改，显然您的客户端方法正在创建一个不可修改的列表(例如使用 Collections#unmodifiableList 等).只需在排序前创建一个可修改的列表:

The list is not modifiable, obviously your client method is creating an unmodifiable list (using e.g. Collections#unmodifiableList etc.). Simply create a modifiable list before sorting:

List<String> modifiableList = new ArrayList<String>(unmodifiableList);
Collections.sort(modifiableList, comparator);

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