Map.Entry interface in Java with example

Map.Entry interface in Java provides certain methods to access the entry in the Map. By gaining access to the entry of the Map we can easily manipulate them. Map.Entry is a generic and is defined in the java.util package.

Declaration :

Interface Map.Entry
k -> Key
V -> Value

Methods:

1. equals (Object o) – It compares the object (invoking object) with the Object o for equality.
   Syntax :

   boolean equals(Object o)
   Parameters :
   o -> Object to which we want to compare
   Returns:
   true: if both objects are equals
   false: otherwise
   

2. K getKey() – Returns the key for the corresponding map entry.
   Syntax :

   K getKey()
   Parameters :
   -------------
   Returns:
   K -> Returns the corresponding Key of a entry on which it is invoked
   

   Exception –

   • IllegalStateException is thrown when entry has been removed from the map.
3. V getValue() – Returns the value for the corresponding map entry.
   Syntax :

   V getValue()
   Parameters :
   -------------
   Returns:
   V -> Returns the corresponding value of a entry on which it is invoked
   

4. int hashcode() – Returns the hashcode for the corresponding map entry.
   Syntax :

   int hashcode()
   Parameters :
   -------------
   Returns:
   int -> Returns the hash-code of entry on which it is invoked
   

5. V setValue(V v) – Sets the value of the map with specified value v

   V setValue(V v)
   Parameters :
   v -> Value which was earlier stored in the entry on which it is invoked
   Returns:
   int -> Returns the hash-code of a entry on which it is invoked

   Exception :

   • ClassCastException is thrown if the class of the value ‘v’ is not a correct type for map.
   • NullPointerException is thrown if ‘null’ is stored in ‘v’, and ‘null ’ is not supported by map.
   • UnsupportedOperationException is thrown if we cannot manipulate the map or the put operation is not supported by the map.
   • IllegalArgumetException is thrown If there is some problem with the argument i.e v
   • IllegalStateException is thrown when entry has been removed from the map

Set<Map.Entry> entrySet() – Returns the Set view of the entire map.
Note : This is not a method of Map.entry interface but it is discussed here because this method is useful while working with Map.Entry interface.

Set<Map.Entry> entrySet() 
Parameters :
---------------
Returns:
Set<Map.Entry> ->: Returns a Set containing the Map.Entry values

Program below demonstrate the working of Map.Entry:

Output:

Before change of value = 1 - Bedroom   25000
After change of value = 1 - Bedroom   59475
Before change of value = 2 - Bedroom   50000
After change of value = 2 - Bedroom   51650
Before change of value = 3 - Bedroom   75000
After change of value = 3 - Bedroom   95200
Before change of value = 1 - Bedroom - hall   65000
After change of value = 1 - Bedroom - hall   74112
Before change of value = 2 - Bedroom - hall   85000
After change of value = 2 - Bedroom - hall   41490
Before change of value = 3 - Bedroom - hall   105000
After change of value = 3 - Bedroom - hall   10902