列表的访问元素 <List <List <List <Object> &gt;&gt;&gt;标题=新的ArrayList <List <List <List <Object> &gt;&gt;&gt;（）;

Question

I have the following list List <List <List <List <Object> >>> titles = new ArrayList <List <List <List <Object> >>> (); and I would like to access the elements of it but I don't know how to do that ..

The list has 1 element that in its turn contains 3 elements and each of those 3 elements contains 6 elements but I don't know how to access each of them.

This is the output of the arraylist when I put it in a listview:

 1 element---> [[[12,"01",1,"Fallo de corriente",0,1],
 2 element---> [12,"01",2,"Nivel m\u00E1ximo (activaci\u00F3n)",0,0],
 3 element--->   [12,"01",3,"Nivel m\u00E1ximo(desactivaci\u00F3n)",0,1]]]

Within each element I have 6 elements as you can see, how can I access element 1 that has 6 elements inside and access each of them?

Answer 1

If you really want to use that kind of structure, you can use something like this, eg to extract title of the first item.

String title1 = titles.get(0).get(0).get(0).get(3).toString();

So you have four levels of hierarchy, titles list is level 1 and get(0) will take the list it contains, get(0) will take first (and only item) of level 2, get(0) will take first out of 3 items of level 3, and finally get(3) will take fourth element of level 4 which is actual title as I can see.

So your title1 should be "Fallo de corriente"

Answer 2

You would probably have to revisit on how you are getting the data. By having ArrayList() inside another ArrayList() inside another ArrayList() ..... is a tiring work with loops iterating throughout the list.

And a nightmare for the programmer to find any error.

However, the general idea of solution would be

Iterating through List<Object>()

for(Object o: objectList){}

Iterating through List<List<Object>>

    for(List<Object> outerObjList: objectListList){
       for(Object innerObject: outerObjList){
       }
    }

And so on... It's complexity grows too much for any good developer to comprehend.

I'd not prefer to write loops for List <List <List <List <Object> >>> titles ever! And Ever! (Sort of a pun!).

If there is no other go (As you are getting it from some other source), I would do write a class to perform the mapping using Jackson ObjectMapper. Going forth, your code might be a little more readable as mentioned here

Please read of how to Structure your Classes and possibility for reducing the level of nesting in loops.Maybe re-organize your data into 2-3 individual Map ? Happy coding!

Answer 3

It sounds as if the storing in lists of lists is superfluous and you are only interested in the values of the inner list. If so, does flatmapping help you for further processing?

List <Object> result = titles.stream()
                            .flatMap(x -> x.stream())
                            .flatMap(y -> y.stream())
                            .collect(Collectors.toList());
System.out.println(result);
//[[12, 01, 1, Fallo de corriente, 0, 1], [12, 01, 2, Nivel máximo (activación), 0, 0], [12, 01, 3, Nivel máximo(desactivación), 0, 1]]

Or add one more step to get a list of each value:

List <Object> result = titles.stream()
                            .flatMap(x -> x.stream())
                            .flatMap(y -> y.stream())
                            .flatMap(z -> z.stream())
                            .collect(Collectors.toList());
System.out.println(result);

//[12, 01, 1, Fallo de corriente, 0, 1, 12, 01, 2, Nivel máximo (activación), 0, 0, 12, 01, 3, Nivel máximo(desactivación), 0, 1]