Persistor.java

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package com.sun.tools.visualvm.api.caching;

/**
 * Generic key/value persistor
 * Supports retrieving a value by the given key and storing a value with the given key
 * @author Jaroslav Bachorik
 */
public interface Persistor<K, V> {
    /**
     * Retrieves {@linkplain Entry} for the given key
     * @param key The key to retrieve {@linkplain Entry} instance
     * @return Returns the retrieved {@linkplain Entry} instance or NULL
     */
    Entry<V> retrieve(K key);
    /**
     * Stores the {@linkplain Entry} together with its key
     * @param key The key to be used
     * @param value The value to be used
     */
    void store(K key, Entry<V> value);

    /**
     * The default (NULL-value) instance
     */
    final public static Persistor DEFAULT = new Persistor() {

        @Override
        public Entry retrieve(Object key) {
            // do nothing
            return null;
        }

        @Override
        public void store(Object key, Entry value) {
            // do nothing
        }

    };
}