Problem in modifying the value in a HashTable in Java

Question

I have created a hashtable in java as: Hashtable<Integer, String> h = new Hashtable<Integer, String>();

Now I have populated some values in this Hashtable as:

1 -> "A"

2 -> "B"

3 -> "C"

4 -> "D"

Now I want to check if a particular key is present in the hashtable. If it is indeed present then I will modify the value part of the HashTable for that particular key. For e.g. I want to check if the key = 2 is present or not. Since it is present I want to modify the value part with 'F'.

So now the entry will look like: 2 -> "B F".

So the Hashtable will become as:

1 -> "A"

2 -> "B F"

3 -> "C"

4 -> "D"

Can someone please suggest me the code to this problem in java.

Many thanks in advance.

Please show some code or work you have done, this is quite straightforward. — Rahul, Apr 20 '20 at 08:12
Please note that Hashtable is an obsolete collection. https://stackoverflow.com/questions/8223125/replacement-for-obsolete-hashtable-class-in-java — HoRn, Apr 20 '20 at 08:20

Kunal Vohra · Accepted Answer · 2020-04-20T08:21:24.667

Well, dont confuse too much here. As you are new first get a solution here.

Hash_table.containsKey(key_element);

You can put that in if condition and do your stuff. Here is full code

    // Java code to illustrate the containsKey() method 
import java.util.*; 

public class Hash_Table_Demo { 
    public static void main(String[] args) 
    { 

        // Creating an empty Hashtable 
        Hashtable<Integer, String> hash_table = 
        new Hashtable<Integer, String>(); 

        // Putting values into the table 
        hash_table.put(1, "A"); 
        hash_table.put(2, "B"); 
        hash_table.put(3, "C"); 
        hash_table.put(4, "D"); 


        // Displaying the Hashtable 
        System.out.println("Initial Table is: " + hash_table); 

        // Checking for the key_element '2' 
        if(hash_table.containsKey(2))){ //true
            hash_table.replace(2, "BF");    // Your Soultion Here
        }; 

        System.out.println("New Table is: " + hash_table); 
    } 
}

Why use `replace()` if you use `containsKey()`? It is a helper method added in Java 8, and is equivalent to `if (map.containsKey(key)) { map.put(key, value); }`, so says the [documentation](https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#replace-K-V-), so it is redundant to use both `containsKey()` and `replace()`. — Andreas, Apr 20 '20 at 08:36

Problem in modifying the value in a HashTable in Java

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