Getting Data in Arraylist of List that Matches Arraylist

Question

I have the following ArrayList:

public static List c = new ArrayList();
c = [1,2,3];

I have the following List in an ArrayList:

public static ArrayList<List<String>> Contact = new ArrayList<List<String>>();
Contact = (["One",1], ["Two", 2], ["Three",3], ["Four", 4])

How can I compare the Lists in away that I get a new list that has the value of:

["One","Two","Three"] ????

Basically: I want to check the integer, see if it exists in the second value of an item in the List, and if so, add the first item, to the new list.

so what did you do in order to achieve this?

Lino
– Lino

2018-08-05 08:48:18 +00:00
Commented Aug 5, 2018 at 8:48 — Lino
– Lino, Commented Aug 5, 2018 at 8:48
I am asking a question! I dont know how.

Ron Arel
– Ron Arel

2018-08-05 08:48:44 +00:00
Commented Aug 5, 2018 at 8:48 — Ron Arel
– Ron Arel, Commented Aug 5, 2018 at 8:48
how you add String and int in an List of Strings??

Youcef LAIDANI
– Youcef LAIDANI

2018-08-05 08:49:29 +00:00
Commented Aug 5, 2018 at 8:49 — Youcef LAIDANI
– Youcef LAIDANI, Commented Aug 5, 2018 at 8:49

Viswanath Kumar Sandu · Accepted Answer · 2018-08-05 09:06:32Z

1

Instead of creating a ArralyList>, Better to use a HashMap

Have data as

c = [1,2,3];

Map<Int, String> data = new HashMap();
data.put(1, "One");
data.put(2, "Two");
data.put(3, "Three");

ArrayList<String> output = new ArrayList()
for(int i=0 i<c.length; i++) {
    output.add(data.get(c[i]));
}

Now output will have the data ["One", "Two", "Three"]

answered Aug 5, 2018 at 9:06

Viswanath Kumar Sandu

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Comments

Community · Accepted Answer · 2020-06-20 09:12:55Z

Ok, If in any case your code look like this :

List<Integer> c = new ArrayList(Arrays.asList(1, 2, 3));
ArrayList<List<String>> contact = new ArrayList<List<String>>();
contact.add(Arrays.asList("One", "1"));
contact.add(Arrays.asList("Two", "2"));
contact.add(Arrays.asList("Three", "3"));
contact.add(Arrays.asList("Four", "4"));

You can use streams like so :

List<String> result = contact.stream()
        .filter(l -> c.contains(Integer.valueOf(l.get(1))))
        .map(l -> l.get(0))
        .collect(Collectors.toList());

this will gives you :

[One, Two, Three]

Better Solution

Rather for a good work, I would create a class Contact which hold id and a name for example :

class Contact{
   private Integer id;
   private String name;

   //constructor getters and setters
}

Then fill your List like so :

ArrayList<Contact> contact = new ArrayList<>();
contact.add(new Contact(1, "One"));
contact.add(new Contact(2, "Two"));
contact.add(new Contact(3, "Three"));
contact.add(new Contact(4, "Four"));

So when you want to search you can use :

List<String> result = contacts.stream()
        .filter(l -> c.contains(l.getId()))
        .map(Contact::getName)
        .collect(Collectors.toList());

It can be more readable and more helpful to work.

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