String[] arr1 = {"abcd", "dfg", "abc"};
String[] arr2 = {"abcd", "ccd", "df", "d", "abc"};
String[] result_union = union(arr1, arr2);
System.out.println("求并集的結(jié)果如下：");
for (String str : result_union) {
  System.out.println(str);
}