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Iterate through the values of Java HashMap example

  1. /*
  2.   Iterate through the values of Java HashMap example
  3.   This Java Example shows how to iterate through the values contained in the
  4.   HashMap object.
  5. */
  6.  
  7. import java.util.Collection;
  8. import java.util.HashMap;
  9. import java.util.Iterator;
  10.  
  11. public class IterateValuesOfHashMapExample {
  12.  
  13.   public static void main(String[] args) {
  14.  
  15.     //create HashMap object
  16.     HashMap hMap = new HashMap();
  17.  
  18.     //add key value pairs to HashMap
  19.     hMap.put("1","One");
  20.     hMap.put("2","Two");
  21.     hMap.put("3","Three");
  22.  
  23.     /*
  24.       get Collection of values contained in HashMap using
  25.       Collection values() method of HashMap class
  26.     */
  27.     Collection c = hMap.values();
  28.  
  29.     //obtain an Iterator for Collection
  30.     Iterator itr = c.iterator();
  31.  
  32.     //iterate through HashMap values iterator
  33.     while(itr.hasNext())
  34.       System.out.println(itr.next());
  35.   }
  36. }
  37.  
  38. /*
  39. Output would be
  40. Three
  41. Two
  42. One
  43. */

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More modern alternative

Submitted by Anonymous on Tue, 05/26/2009 - 14:03.

I would recommend to use something like:

  1. for (Object key: hMap.keySet()) {
  2.     System.out.println(hMap.get(key));
  3. }

Or even better with a hMap using generics:
  1. for (Map.Entry<int, String> entry: hMap.entrySet()) {
  2.     System.out.println(entry.getValue());
  3. }

Very helpful! Thanks!

Submitted by Anonymous on Thu, 05/28/2009 - 18:29.

Very helpful! Thanks!

hm

Submitted by Anonymous on Tue, 06/09/2009 - 19:15.

why is it not working if i try to work with the values which itsself are objects of another class ?

  1.        Collection c = allLendings.values();     
  2.        Iterator itr = c.iterator();
  3.  
  4.         while(itr.hasNext())
  5.         {
  6.             String[] date = itr.next().getLend().split(".");
  7.             if(date[1] == month)
  8.             {
  9. .                   ....
  10.             }
  11. }

Iterator returns object

Submitted by Anonymous on Thu, 06/11/2009 - 17:43.

Hi,

Iterator's next method returns object. So you need to cast it to appropriate class before invoking its method.

Hope this helps.
Thanks.

This is better

Submitted by Anonymous on Sat, 07/11/2009 - 15:57. 

  1. Iterator hashIterator = hashMapName.keySet().iterator();
  2. while(hashIterator.hasNext()) {
  3.     Type variable = hashIterator.next();
  4.     Type2 variable2 = hashMapName.get(variable);
  5.     ...
  6. }

I like the first one better

Submitted by Anonymous on Thu, 07/30/2009 - 21:57.

Because it is compact

  1. for (Object key: hMap.keySet()) {
  2.  System.out.println(hMap.get(key));
  3. }

very good

Submitted by Anonymous on Thu, 07/30/2009 - 21:58.

Thanks for the better example.
It is easy to read and very compact.

Why not just use: for (

Submitted by Anonymous on Fri, 07/31/2009 - 14:49.

Why not just use:

  1. for ( Object x : hMap.values() ) {
  2.    System.out.println(x);
  3. }

is it bad?

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