Hashtable put() Method in Java
Last Updated :
28 Jun, 2018
The java.util.Hashtable.put() method of Hashtable is used to insert a mapping into a table. This means we can insert a specific key and the value it is mapping to into a particular table. If an existing key is passed then the previous value gets replaced by the new value. If a new pair is passed, then the pair gets inserted as a whole.
Syntax:
Hash_Table.put(key, value)
Parameters: The method takes two parameters, both are of the Object type of the Hashtable.
- key: This refers to the key element that needs to be inserted into the Table for mapping.
- value: This refers to the value that the above key would map into.
Return Value: If an existing key is passed then the previous value gets returned. If a new pair is passed, then NULL is returned.
Below programs are used to illustrate the working of java.util.Hashtable.put() Method:
Program 1: When passing an existing key.
import java.util.*;
public class Hash_Table_Demo {
public static void main(String[] args)
{
Hashtable<Integer, String> hash_table =
new Hashtable<Integer, String>();
hash_table.put( 10 , "Geeks" );
hash_table.put( 15 , "4" );
hash_table.put( 20 , "Geeks" );
hash_table.put( 25 , "Welcomes" );
hash_table.put( 30 , "You" );
System.out.println( "Initial table is: " + hash_table);
String returned_value = (String)hash_table.put( 20 , "All" );
System.out.println( "Returned value is: " + returned_value);
System.out.println( "New table is: " + hash_table);
}
}
|
Output:
Initial table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Returned value is: Geeks
New table is: {10=Geeks, 20=All, 30=You, 15=4, 25=Welcomes}
Program 2: When passing a new key.
import java.util.*;
public class Hash_Table_Demo {
public static void main(String[] args)
{
Hashtable<Integer, String> hash_table =
new Hashtable<Integer, String>();
hash_table.put( 10 , "Geeks" );
hash_table.put( 15 , "4" );
hash_table.put( 20 , "Geeks" );
hash_table.put( 25 , "Welcomes" );
hash_table.put( 30 , "You" );
System.out.println( "Initial table is: " + hash_table);
String returned_value = (String)hash_table.put( 50 , "All" );
System.out.println( "Returned value is: " + returned_value);
System.out.println( "New table is: " + hash_table);
}
}
|
Output:
Initial table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Returned value is: null
New table is: {10=Geeks, 20=Geeks, 30=You, 50=All, 15=4, 25=Welcomes}
Note: The same operation can be performed with any type of variation and combination of different data types.
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