How to add two list of item same type in generic list in java

Question

i have one method which accept List<?> i want to two list i want to add two list in single generic list but i am unable to add i tried to create one generic type list but its not accepting.

I tried this:

List<Object> list = new ArrayList<>();
list.add(model.getfirstlist().getItems());                      
list.add(model.getSecondlist().getItems());
setListData(list)

My function is:

public void setListData(List<?> list) {
       // print list
}

getItems have field same field id, title

setListData(model.getfirstlist().getItems()) // working fine

My function is like

public void setListData(List<?> list) {
       // print list
}

I am trying to add two list in single list and pass it into

singlelist = ( model.getfirstlist().getItems() +
model.getSecondlist().getItems())
setListData(singlelist);

Please suggest me how i will do this.

You want the addAll method of List.

VGR
– VGR

2019-03-28 15:12:55 +00:00
Commented Mar 28, 2019 at 15:12 — VGR
– VGR, Commented Mar 28, 2019 at 15:12
yes @VGR we have two list with same type

MARSH
– MARSH

2019-03-28 15:13:32 +00:00
Commented Mar 28, 2019 at 15:13 — MARSH
– MARSH, Commented Mar 28, 2019 at 15:13

VGR · Accepted Answer · 2019-03-28 15:23:30Z

1

Use the addAll method of Collection and List:

List<Item> list = new ArrayList<>();
list.addAll(model.getfirstlist().getItems());                      
list.addAll(model.getSecondlist().getItems());
setListData(list);

answered Mar 28, 2019 at 15:23

VGR

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Comments

Christos · Accepted Answer · 2019-03-28 15:20:45Z

1

You can create a List that would contain as elements both lists:

e.g.

List<Integer> listA = Arrays.asList(1,2,3,4,5);
List<Integer> listB = Arrays.asList(6,7,8,9);

List<List<Integer>> lists = Arrays.asList(listA, listB);

Then using streams api you could flatten the list you have created try the following:

List<Object> flattenList = Stream.of(lists)
                                 .flatMap(x -> x.stream())
                                 .collect(Collectors.toList());

If you can't use stream api you can try the following approach:

List<Integer> listA = Arrays.asList(1,2,3,4,5);
List<Integer> listB = Arrays.asList(6,7,8,9);

listA.addAll(listB);

Now listA would contain also the items of listB.

edited Mar 28, 2019 at 15:20

answered Mar 28, 2019 at 14:54

Christos

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8 Comments

MARSH Over a year ago

Thanks for answer let me try your answer.

MARSH Over a year ago

we can not use Stream API there is some version issue with stream API do you have any other solution .

Christos Over a year ago

@MARSH What version of Java you use ? Stream API has been inserted in Java 8.

MARSH Over a year ago

I am using java 8 but when i use this Android then there is some SDK version issue is coming we cant go with Stream API

MARSH Over a year ago

we have not integer type we have Item type object.

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