如何在JAVA中實現一個固定最大size的hashMap

如何在JAVA中實現一個固定最大size的hashMap

利用LinkedHashMap的removeEldestEntry方法，重載此方法使得這個map能夠增加到最大size，以後每插入一條新的記錄就會刪除一條最老的記錄。

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

public class MaxSizeHashMap<K, V> extends LinkedHashMap<K, V> {
    private final int maxSize;

    public MaxSizeHashMap(int maxSize) {
        this.maxSize = maxSize;
    }


    //
    //Returns true if this map should remove its eldest entry. 
    //This method is invoked by put and putAll after inserting a new entry into the map. 
    //It provides the implementor with the opportunity to remove the eldest entry each time a new 
    //one is added. This is useful if the map represents a cache: 
    //    it allows the map to reduce memory consumption by deleting stale entries. 
    //
    @Override
    protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
        return size() > maxSize;
    }
}