Java LinkedHashMap
Java LinkedHashMap
A LinkedHashMap stores keys and values, and keeps them in the same order you put them in.
It is part of the java.util package and implements the Map interface.
Tip: Use LinkedHashMap when you want predictable iteration order (insertion order).
Create a LinkedHashMap
Create a LinkedHashMap object called capitalCities that will store
String keys and String values:
Example
import java.util.LinkedHashMap; // Import the LinkedHashMap class
LinkedHashMap<String, String> capitalCities = new LinkedHashMap<>();
Now you can use methods like put() to add key/value pairs,
get() to retrieve a value by key,
and remove() to delete an entry - all while maintaining insertion order.
Add Items
Use the put() method to add items to the LinkedHashMap:
Example
// Import the LinkedHashMap class
import java.util.LinkedHashMap;
public class Main {
public static void main(String[] args) {
LinkedHashMap<String, String> capitalCities = new LinkedHashMap<>();
capitalCities.put("England", "London");
capitalCities.put("India", "New Dehli");
capitalCities.put("Austria", "Wien");
capitalCities.put("Norway", "Oslo");
capitalCities.put("Norway", "Oslo"); // Duplicate
capitalCities.put("USA", "Washington DC");
System.out.println(capitalCities);
}
}Output: The items will appear in the order they were added (e.g., {England=London, India=New Dehli, Austria=Wien, Norway=Oslo, USA=Washington DC}).
Note: Duplicates like "Norway" are ignored.
Access an Item
Use get() with a key to get its associated value:
Remove an Item
Use remove() to remove an item by key:
Use clear() to remove all items:
LinkedHashMap Size
Use size() to check how many key/value pairs are in the map:
Note: The size only counts unique keys. If a key is added more than once, only the latest value is kept.
Loop Through a LinkedHashMap
You can loop through a LinkedHashMap using a for-each loop. Use:
keySet()to get all keysvalues()to get all values
Example
// Print keys
for (String key : capitalCities.keySet()) {
System.out.println(key);
}Example
// Print values
for (String value : capitalCities.values()) {
System.out.println(value);
}Example
// Print keys and values
for (String key : capitalCities.keySet()) {
System.out.println("Key: " + key + ", Value: " + capitalCities.get(key));
}HashMap vs LinkedHashMap
| Feature | HashMap |
LinkedHashMap |
|---|---|---|
| Order | No guaranteed order | Insertion order preserved |
| Performance | Faster for random access | Slightly slower due to ordering |
| Duplicates | Keys must be unique | Keys must be unique |
Tip: Use LinkedHashMap when you want the map to remember the order in which entries were added.
