我通过eclipse执行了您的程序：
只需使用LinkedList<Integer>而不是LinkedList。没有警告。
输出=>
CONTENTS OF l1 = []
SIZE = 0
CONTENTS OF ll = [10, 20, 30, 40]
SIZE = 4
SUM USING toArray () = 100
CONTENTS OF ll = [6, 5, 10, 20, 30, 40]
SIZE = 6
SUM USING iterator () = 111
6,5,10,20,30,40,
Exception in thread "main" java.util.NoSuchElementException
at java.util.LinkedList$ListItr.next(UnkNown Source)
at com.Linkedlist.main(Test.java:46)
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