IdentityHashMap put() Method in Java
Last Updated :
24 Jul, 2018
The java.util.IdentityHashMap.put() method of IdentityHashMap is used to insert a mapping into a map. This means we can insert a specific key and the value it is mapping, into a particular map. 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:
Identity_Hash_Map.put(key, value)
Parameters: The method takes two parameters, both are of the Object type of the IdentityHashMap.
- key: This refers to the key element that needs to be inserted into the Map 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.IdentityHashMap.put() Method:
Program 1: When passing an existing key.
import java.util.*;
public class Identity_Hash_Map_Demo {
public static void main(String[] args)
{
Map<Integer, String> identity_hash = new IdentityHashMap<Integer, String>();
identity_hash.put( 10 , "Geeks" );
identity_hash.put( 15 , "4" );
identity_hash.put( 20 , "Geeks" );
identity_hash.put( 25 , "Welcomes" );
identity_hash.put( 30 , "You" );
System.out.println( "Initial Mappings are: " + identity_hash);
String returned_value = (String)identity_hash.put( 20 , "All" );
System.out.println( "Returned value is: " + returned_value);
System.out.println( "New map is: " + identity_hash);
}
}
|
Output:
Initial Mappings are: {10=Geeks, 30=You, 20=Geeks, 25=Welcomes, 15=4}
Returned value is: Geeks
New map is: {10=Geeks, 30=You, 20=All, 25=Welcomes, 15=4}
Program 2: When passing a new key.
import java.util.*;
public class Identity_Hash_Map_Demo {
public static void main(String[] args)
{
Map<Integer, String> identity_hash = new IdentityHashMap<Integer, String>();
identity_hash.put( 10 , "Geeks" );
identity_hash.put( 15 , "4" );
identity_hash.put( 20 , "Geeks" );
identity_hash.put( 25 , "Welcomes" );
identity_hash.put( 30 , "You" );
System.out.println( "Initial Mappings are: " + identity_hash);
String returned_value = (String)identity_hash.put( 50 , "All" );
System.out.println( "Returned value is: " + returned_value);
System.out.println( "New map is: " + identity_hash);
}
}
|
Output:
Initial Mappings are: {10=Geeks, 30=You, 20=Geeks, 25=Welcomes, 15=4}
Returned value is: null
New map is: {10=Geeks, 30=You, 20=Geeks, 25=Welcomes, 15=4, 50=All}
Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.
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