java面试记录

Posted 2021-02-15 heliusking

1. 怎么确保一个集合不能被修改

    

   ArrayList<String> list = new ArrayList<>();
   list.add("x");
   Collection<String> clist = Collections.unmodifiableCollection(list);
   clist.add("y"); // 运行时出异常：java.lang.UnsupportedOperationException
   System.out.println(list.size());

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