LinkedHashMap removeEldestEntry() Method in Java

The removeEldestEntry() method of LinkedHashMap is used to automatically remove old entries based on a custom condition. It is mainly used to limit map size and implement cache-like behavior, such as LRU (Least Recently Used) caching.

Java

import java.util.*;

public class LinkedHashMapDemo {
    private static final int MAX = 6;

    public static void main(String[] args) {

        LinkedHashMap<Integer, String> map =
            new LinkedHashMap<Integer, String>() {
                @Override
                protected boolean removeEldestEntry(
                        Map.Entry<Integer, String> eldest) {
                    return size() > MAX;
                }
            };
        map.put(0, "Welcome");
        map.put(1, "To");
        map.put(2, "The");
        map.put(3, "World");
        map.put(4, "Of");
        map.put(5, "geeks");

        System.out.println(map);

        map.put(6, "GeeksforGeeks");
        System.out.println(map);

        map.put(7, "Hello");
        System.out.println(map);
    }
}

Output

{0=Welcome, 1=To, 2=The, 3=World, 4=Of, 5=geeks}
{1=To, 2=The, 3=World, 4=Of, 5=geeks, 6=GeeksforGeeks}
{2=The, 3=World, 4=Of, 5=geeks, 6=GeeksforGeeks, 7=Hello}

Explanation:

The map is limited to 6 entries using MAX.
When a new entry causes the size to exceed the limit, the eldest entry is removed.
Removal happens automatically after insertion.
Entries are removed in insertion order (default behavior).

Syntax

protected boolean removeEldestEntry(Map.Entry<K, V> eldest)

Parameters:

eldest : Represents the eldest entry in the map.

In insertion-order: least recently inserted entry
In access-order: least recently accessed entry

If the map contained only one entry before insertion, that entry is both the eldest and newest.
Return Value:

true : remove the eldest entry
false : retain the entry

Example: LRU Cache Using Access Order

Java

import java.util.*;

public class GFG {

    public static void main(String[] args){

        LinkedHashMap<Integer, String> cache
            = new LinkedHashMap<Integer, String>(16, 0.75f,
                                                 true){
                  @Override
                  protected boolean removeEldestEntry(
                      Map.Entry<Integer, String> eldest)
                  {
                      return size() > 3;
                  }
              };

        cache.put(1, "A");
        cache.put(2, "B");
        cache.put(3, "C");

        cache.get(1);
        
        // Removes least recently used entry
        cache.put(4, "D"); 

        System.out.println(cache);
    }
}

Output

{3=C, 1=A, 4=D}

Explanation:

The map uses access order (true in constructor).
Entry 2 is removed because it is the least recently accessed.
This behavior mimics a simple LRU cache.

LinkedHashMap removeEldestEntry() Method in Java

Syntax

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