程序代码：

import java.util.*;

public class ListRemoveDuplicate {

    public static void main(final String[] args) {
        List<Object> testList = new ArrayList<>();

        List<Object> elementList1 = new ArrayList<>();
        elementList1.add("1");
        elementList1.add("2");
        elementList1.add("3");

        List<Object> elementList2 = new ArrayList<>();
        elementList2.add("4");
        elementList2.add("5");
        elementList2.add("6");

        List<Object> elementList3 = new ArrayList<>();
        elementList3.add("1");
        elementList3.add("2");
        elementList3.add("3");

        testList.add(elementList1);
        testList.add(elementList2);
        testList.add(elementList3);

        System.out.println("before:" + testList);

        System.out.println("after:" + removeDuplicate(testList));
    }

    public static List removeDuplicate(final List inputList) {
        HashSet<Object> hashSet = new HashSet<>(inputList);
        List<Object> outputList = new ArrayList<>();
        outputList.addAll(hashSet);
        return outputList;
    }
}

before:[[1, 2, 3], [4, 5, 6], [1, 2, 3]]
after:[[1, 2, 3], [4, 5, 6]]