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Thread: hash map iteration

  1. #1
    Junior Member
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    Sep 2011
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    Default hash map iteration

    i have a problem in iterating hashmap..
    it gives me values in reverse order...why so..please help me...
    here is my code..
    cart="1.1,2.2,3.3,1.1";// cart variable

    String[] cart_items=cart.split(",");// spliting cart by ' , '

    HashMap<String,Integer> hashmap=new HashMap(); // create a new hashmap
    for(String i:cart_items)// iterate through cart_items

    if(hashmap.containsKey(i)) //if hashmap contains key increment value by 1
    hashmap.put(i, f); // if hashmap doesnt contain key put its values as 1
    //now i want to iterate through this hashmap....

    for(Object j:hashmap.keySet() )
    out.println("key=" + i + " and value= " + hahsmap.get(i) );


    /////////////// now this should give me output as..
    key=1.1 and value=2
    key=2.2 and value=1
    key=3.3 and value=1

    ////////////but it gives me output as....

    key=3.3 and value=1
    key=2.2 and value=1
    key=1.1 and value=2


    please help me why this is giving me such output..........................

  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: hash map iteration

    You don't control the order you get the keys in a HashMap. Maps aren't really designed for sequential iteration- instead, they're designed to make "give me this thing that might be in the middle somehwere" fast. You might look at a TreeMap instead.

    Alternatively, you could look into sorting the key set, or you could just use the array of keys to get them in the order you want them.

    Although, this does bring up the question- why are you using a Map in the first place?
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  3. #3
    Administrator copeg's Avatar
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    Default Re: hash map iteration

    To add to Kevin's advice, if you want order of iteration to remain the same as order of addition for a Map, use a LinkedHashMap.

  4. The Following User Says Thank You to copeg For This Useful Post:

    KevinWorkman (September 10th, 2011)

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