How do you sort numeric values stored in a hashmap then in an ArrayList in Java?

Question

I have an ArrayList.

Each element is a HashMap lookup for my values.

1 of the values is numeric.

I'm using Collections.sort() for alpha sorting. But the numbers are getting alpha sorted, instead of numeric sorted.

protected ArrayList<HashMap<String, String>> myAccountList;

String Name = myAccountList.get(i).get("accountName");
Double balance = Double.valueOf(myAccountList.get("accountBalance"));  //is a number stored as a string

So I have the sort working on accountName just fine.

Collections.sort(myAccountList, new Comparator(){
   public int compare(Object o1, Object o2) {
      HashMap<String,String> old1 = (HashMap<String, String>) o1;
      HashMap<String,String> old2 = (HashMap<String, String>) o2;
      return old1.get("accountName").compareToIgnoreCase(old2.get("accountName"));
   }
});

How would I sort the field accountBalance as a number? I doubt it matters, but I'm programming an Android app.

Why not store balances as a Double instead? For example, HashMap<String, Double> — Paul Bellora
– Paul Bellora, Commented Sep 30, 2011 at 1:30
OK, I can do that. But what would the sort look like? And how do I get the HashMap to accept <String, String> as well as <String, Double> ?? — kireol
– kireol, Commented Sep 30, 2011 at 1:32
You can't do that if you're holding strings as well as doubles in the map. You could however use a HashMap<String, Object>. — Don Roby
– Don Roby, Commented Sep 30, 2011 at 1:36
@DonRoby is right. Don't use a HashMap at all - see my answer. — Paul Bellora
– Paul Bellora, Commented Sep 30, 2011 at 1:41

Paul Bellora · Accepted Answer · 2011-09-30 01:57:43Z

It looks like you're using a HashMap where you should design your own class:

public class Account {

   public final String name;
   public final Double balance;

   public Account(String name, Double balance) {
      this.name = name;
      this.balance = balance;
   }
}

^{(Note: currently this class is immutable. To make it mutable, change the fields from public final to private and add getters/setters)}

Then you can store them in a List<Account> and sort accordingly:

//sort by name
Collections.sort(myAccountList, new Comparator<Account>(){
   public int compare(Account acc1, Account acc2) {
      return acc1.name.compareTo(acc2.name);
   }
});

//sort by balance
Collections.sort(myAccountList, new Comparator<Account>(){
   public int compare(Account acc1, Account acc2) {
      return acc1.balance.compareTo(acc2.balance);
   }
});

Note the use of a Comparator with the generic type parameter <Account>, so you don't have to cast the compareTo() arguments from Object.

xthexder · Accepted Answer · 2011-09-30 01:36:23Z

2

You will have to do something like this:

Double.valueOf(old1.get("accountBalance")).compareTo(Double.valueOf(old2.get("accountBalance")));

To sort by both the account name and balance, you would check if the first compare is 0 (they are equal) and if so, return the accountBalance compare, assuming you are sorting by account name first.

answered Sep 30, 2011 at 1:36

xthexder

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