same key for diff values in HashMap

[Reshma Reddy]

Hi All,

I want to assign same key but different values in hashmap, Map key is unique right

Ex:

  HashMap<String, String> hashmap = new HashMap<String, String>();
		hashmap.put("fruit", "mango");
		hashmap.put("fruit", "apple");
		hashmap.put("fruit", "orange");
		hashmap.put("fruit", "banana");  

like this I want to add, how can I achieve this in hashmap.

regards,
vardhan

[Christophe Verré]

You could use a List to hold the values, and assign "fruit" to that List.

[Reshma Reddy]

[Not-so-nice response removed. Antagonizing people who are trying to help you is not a winning strategy.]

[Monu Tripathi]

What (I think) Christopher meant was this...

List<String> fruitsList = new ArrayList<String>();
fruitsList .add("mango");
fruitsList .add("apple");
fruitsList .add("orange");
fruitsList .add("banana");

HashMap <String,List<String>>map = new HashMap<String,List<String>>();
hashmap.put("fruit", fruitsList);   

[Garrett Rowe]

vardhan reddy wrote:Hi All,

I want to assign same key but different values in hashmap, Map key is unique right

Ex:

  HashMap<String, String> hashmap = new HashMap<String, String>();
		hashmap.put("fruit", "mango");
		hashmap.put("fruit", "apple");
		hashmap.put("fruit", "orange");
		hashmap.put("fruit", "banana");  

like this I want to add, how can I achieve this in hashmap.

regards,
vardhan

if this were possible, what should be printed here?

System.out.println(hashmap.get("fruit"));

[Reshma Reddy]

monu thanks for your reply..

hashmap is not taking list as argument, it is giving error: change fruitsList to String

Garrett

the out put is banana only it will overried .

regards,
vardhan

[Christophe Verré]

hashmap is not taking list as argument, it is giving error

What kind of error do you have ? Please post the exact error message.

[Reshma Reddy]

chris,

error is::The method put(String, String) in the type HashMap<String,String> is not applicable for the arguments
(String, List<String>)

we are passing list as argument here.

[Jaydeep Mazumdar]

Change the HashMap construtor to this:

HashMap<String, java.util.List> hashmap = new HashMap<String, java.util.List>();   

[Reshma Reddy]

jay,

this the error::

The method put(String, String) in the type HashMap<String,String> is not applicable for the arguments
(String, List<String>)

[Christophe Verré]

vardhan reddy wrote:jay,

this the error::

The method put(String, String) in the type HashMap<String,String> is not applicable for the arguments
(String, List<String>)

You're not even trying Monu's code, are you ?

[Garrett Rowe]

vardhan reddy wrote:
Garrett

the out put is banana only it will overried .

regards,
vardhan

I know what the output is, what do you want the ouptut to be?

[Reshma Reddy]

Chris

I am checking with monu's code only in that one only I am getting this error.

Garrett

Expected out put is for same kay I want different values as i mention in my first post.

[Garrett Rowe]

That doesn't make sense. If you call hashmap.get("fruit"), and you have multiple values for the key "fruit", do you want it to return an array, a List, a comma separated String? How do you want to receive these different values?

[Reshma Reddy]

Expected output is::

fruit: mango
fruit apple
fruit: orange
fruit: banana

[Christophe Verré]

I'm not here to give you any straight answers, but think a few minutes about it :
1. The problem with a map is that you can assign only one value per key
2. To assign several values per key, we suggested you to use a Map<String, List><String>>. The values are stored in a List, and the List is assigned to the key of the map

Try to find out how :
1. To iterate through the Map. What is the type of each value ?
=> Hint: It's not different from any other Map
2. To iterate through each value.
=> Hint: How do you iterate through a List

[Garrett Rowe]

Is that just a single "\n" separated String? That's easy then

public class OneToManyMap
   
    private Map<String, String> map;

    public OneToManyMap() {
       map = new HashMap<String, String>();
   }

   public boolean put(String key, String value) {
      String curr = map.get(key);
      if (curr == null) {
         map.put(key, key + ": " + value);
      } else {
         map.put(key, curr + "\n" + key + ": " + value);
      }
      return true;
   }

   public String get(String key) {
      return map.get(key);
   }
}

[Rob Spoor]

That's quite nasty Garret. What if you want to remove one of the values, but not the rest? Or iterate over all the values for one key?

[Garrett Rowe]

Rob Prime wrote:That's quite nasty Garret.

I thought if I put the very dirty version out there it might motivate the OP to clarify his requirements.

What if you want to remove one of the values, but not the rest? Or iterate over all the values for one key?

I'll leave contains() and remove() as an exercise for the reader.