Java Hashtable : one key - two value, how to get both of them?

Question

My problem is that I have an Hashtable and I end up with some key having two values. I would like to get both of these value, so I can see which one I want and take it.

Here is an exemple :

Hashtable<String, String> myTable = new Hashtable<>();
myTable.put("key1", "value1");
myTable.put("key1", "value2");
System.out.println(myTable.get("key1"));
//output : value2

How to retrieve both of the value ?

Thank you for your help !

EDIT : In my tests, the HashTable can't store 2 values like this but I assure that in my project where I have a (I believe) code that does the same thing. When, after my algorithm has ran I System.out.prinln(myTable) it does show multiple time the same key with differents value.

Also take a look at this: [hashmap vs. hashtable](https://stackoverflow.com/questions/40471/differences-between-hashmap-and-hashtable). — andrewJames, Apr 11 '20 at 14:16
@andrewjames It partially answer. I think the problem comes from the fact that I work with Object and I constantly makes new ones. So it does not consider the keys to be the same thing. So I should probably rewrite this code — Virgil, Apr 11 '20 at 14:21
Have you considered using a pair object as a value into your hash table — GilbertS, Apr 11 '20 at 14:41

score 0 · Answer 1 · answered Apr 11 '20 at 14:21

0

In HashMap class, put function adds object if it isn't exist, if it's exist just updates the value. You can create another class to keep values;

class exampleValue {
    String v1, v2;

    exampleValue() {}
}

and

HashMap<String, exampleValue> h = new HashMap<>();

exampleValue v = new exampleValue();
v.v1 = "a";
v.v2 = "b";

h.put("key", v);

h.get("key").v1; //returns "a"
h.get("key").v2; //returns "b"

answered Apr 11 '20 at 14:21

Atahan Atay

363
2
15

I see the problem. I need to change the second type to something like you said or maybe an Array – Virgil Apr 11 '20 at 14:23
@Virgil Sorry, I couldn't understand. What do you want to do? – Atahan Atay Apr 11 '20 at 14:27
I need change the value type of my Hashtable to something that can store multiple value. Maybe the exampleValue you suggest or an Array. – Virgil Apr 11 '20 at 14:29
Oh, I understand. – Atahan Atay Apr 11 '20 at 14:33

score 0 · Accepted Answer · answered Apr 11 '20 at 14:27

It depends on the way to create a HashTable, in your example. You create a HashTable maps a String to a String, then because the value is a String, you cannot expect the table can store multiple values on one key. When you do the second put method, it will find the key with value key1 and replace the previous value which is mapped to this key to the new one.

If you want to store multiple values on one key, think about the list which will hold multiple values for your key. Here is an example to map a key with a type of String to multiple String values:

Hashtable<String, ArrayList<String>> myTable = new Hashtable<>();
ArrayList<String> listValue = new ArrayList<>();
listValue.add("value1");
listValue.add("value2");
myTable.put("key1", listValue); 
System.out.println(myTable.get("key1")); // get all values of the key [value1, value2]
System.out.println(myTable.get("key1").get(0)); // get the first value of this key, value1
System.out.println(myTable.get("key1").get(1)); // get the second value of this key, value2

It is recommended to use HashMap over a HashTable.

Java Hashtable : one key - two value, how to get both of them?

2 Answers2