java.lang.UnsupportedOperationException List.clear

素颜马尾好姑娘i 2021-10-19 12:18 303阅读 0赞

用Set实现List去重的代码

public static <S> List<S> removeDedupElement(List<S> list) {
    		TreeSet<S> set = new TreeSet<S>(list);
    		list.clear();
    		list.addAll(set);
    		return list;
    	}

调用

System.out.println(removeDedupElement(Arrays.asList(new String[]{"qqq","qqq","www","www"})));
            
            List<String> list = new LinkedList<String>(Arrays.asList(new String[]{"qqq","qqq","www","www"}));
            System.out.println(removeDedupElement(list));

第一个会报错

at java.util.AbstractList.remove(AbstractList.java:161)
    	at java.util.AbstractList$Itr.remove(AbstractList.java:374)
    	at java.util.AbstractList.removeRange(AbstractList.java:571)
    	at java.util.AbstractList.clear(AbstractList.java:234)
    	at com.xxx.yyy.dqm.utils.CollectionUtils.removeDedupElement(LdBankCollectionUtils.java:10)

主要时由于Arrays.asList返回的是java.util.Arrays.ArrayList<E>， 这个跟java.util.ArrayList 都继承AbstractList ，但是java.util.Arrays.ArrayList<E>没有自己实现remove等方法，

public E remove(int index) {
            throw new UnsupportedOperationException();
        }