Java LinkedHashMap.removeEldestEntry method example

How it works

• removeEldestEntry is always invoked after an element is inserted.
• Based on the method’s return value:
  • Returns true: The oldest entry is removed.
  • Always returns true: The map continuously removes entries (will become empty).
  • Returns false: Nothing is removed; behaves like a normal LinkedHashMap.

After every put or putAll insertion, the eldest element may be removed depending on the logic. The JavaDoc provides a clear example of this usage.

Example: removeEldestEntry

import java.util.LinkedHashMap;
import java.util.Map;

public class MapRemoveEntry {

    public static void main(String[] args) {

        LinkedHashMap<Integer, String> map = new LinkedHashMap<Integer, String>() {
            private static final long serialVersionUID = 1L;

            @Override
            protected boolean removeEldestEntry(Map.Entry<Integer, String> eldest) {
                return size() > 4;
            }
        };

        map.put(0, "A");
        map.put(1, "B");
        map.put(2, "C");
        map.put(3, "D");
        map.put(4, "E");

        map.forEach((k, v) -> System.out.println("key = " + k + " value = " + v));
    }
}
            

Output:

Explanation: The method removeEldestEntry returns true when the map size is greater than 4. This removes the oldest entry (key=0, value=A).

Summary

Using removeEldestEntry, you can control when to remove the oldest entry from a map. This is particularly useful for implementing caches where you want to limit the number of stored items.