HashMap<String, ArrayList<String>>

Question

I am trying to get HashMap store a String and a ArrayList<String>. Basicly what I want is for the first String to be a Name, and the arraylist to contain every country the user have been to.

Example:
{Andrew, [USA, China]}
{Lola, [Sweden, Denmark]}

The problem I meet is whenever the user puts in a country, the country will be stored under both names:

"The HashMap contains: {Andrew=[USA, China, Sweden, Denmark], Lola=[USA, China, Sweden, Denmark]}"

ArrayList<String> namelist = new ArrayList<>();
ArrayList<String> test = new ArrayList<>();
ArrayList<String> archive = new ArrayList<>();
HashMap<String, ArrayList<String>> thearchive = new HashMap<>();

(input.equals("New Country")){
    System.out.println("Name of the Person? ");
    String name = in.nextLine();
    if(namelist.contains(name)){
        System.out.println("Which Country have you visited?");
        String country = in.nextLine();
        if (archive.contains(country)){
            System.out.println("You've already visited this country.");
        }
        else {
            test.add(country);
            thearchive.put(name, country);
            System.out.println("HashMap Contains: " + thearchive);
        }
    }
    else{
        System.out.println("The person does not exist please add first.");
    }

Does someone knows why the HashMap is not storing the key/values the way I want too?

You need to provide the rest of your code.

aarti
– aarti

2014-11-14 00:44:31 +00:00
Commented Nov 14, 2014 at 0:44 — aarti
– aarti, Commented Nov 14, 2014 at 0:44

augustoccesar · Accepted Answer · 2014-11-14 00:53:34Z

1

Your code is nota completed so I can't know what is test an thearchive. But let's create an example:

HashMap<String, ArrayList<String>> list = new HashMap<String, ArrayList<String>>();
ArrayList<String> anotherlist = new ArrayList<String>();
anotherlist.add("Brazil");
anotherlist.add("USA");
list.put("Augusto", anotherlist);

I hope it helps.

answered Nov 14, 2014 at 0:53

augustoccesar

6669 silver badges30 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Hablo Over a year ago

The problem with that is that I need to take name and countries from the user through System.in.

Hovercraft Full Of Eels · Accepted Answer · 2014-11-14 01:05:33Z

1

Usually your problem is due to re-using the same ArrayList for all people, so that all folks share the same Countries, all held by the one single ArrayList. A solution is to create a new ArrayList for each person -- meaning new ArrayList<String> needs to be inside some loop where you create your traveler's name String.

So for example, you could change your code to this:

ArrayList<String> namelist = new ArrayList<>();
ArrayList<String> test = new ArrayList<>();

// ArrayList<String> archive = new ArrayList<>();

HashMap<String, ArrayList<String>> arkivet = new HashMap<>();

(input.equals("New Country")){
    System.out.println("Name of the Person? ");
    String name = in.nextLine();

    archive = ArrayList<String>(); // **********
    arkivet.put(name, archive);  // ************

    if(namelist.contains(name)){
        System.out.println("Which Country have you visited?");
        String country = in.nextLine();
        if (archive.contains(country)){
            System.out.println("You've already visited this country.");
        }
        else {
            test.add(country);
            thearchive.put(name, country);
            System.out.println("HashMap Contains: " + thearchive);
        }
    }
    else{
        System.out.println("The person does not exist please add first.");
    }

edited Nov 14, 2014 at 1:05

answered Nov 14, 2014 at 0:44

Hovercraft Full Of Eels

286k25 gold badges267 silver badges391 bronze badges

4 Comments

Hablo Over a year ago

Thanks, will try the code to see where it gets me :)

Hablo Over a year ago

What does these two lines of code do? "archive = = ArrayList<String>(); // **********", "arkivet.put(name, archive); // ************" Because I just get illegal start of expression when running the program on those lines

Hovercraft Full Of Eels Over a year ago

@Hablo: typo. This happens because I'm working with code snippets that I can't compile, so I can't have a compiler notify me of when my fat fingers are farking up.

Hovercraft Full Of Eels Over a year ago

@Hablo: but regardless, don't copy my code, copy my ideas. Re-initialize the ArrayList that holds the country names inside of the loop where you create the traveler.

Collectives™ on Stack Overflow

HashMap<String, ArrayList<String>>

2 Answers 2

1 Comment

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related