Please, only one condition

Question about the task

Resolved

How can you pass 7th and 8th conditions at the same time? They're opposite for each other. If you find element in cache, you cannot search for the element in storage(Condition 6), but if you don't search you cannot pass condition 7. Please help, I'm confused.....

The Proxy pattern provides an object that controls access to another object.

You need to create a CachingProxyRetriever class in the retrievers package. It will provide the same functionality as the OriginalRetriever class, but with one important addition. You need to always try to first get the object from a cache, and only perform the expensive operation of loading it from storage if it is not in the cache. After the required object is retrieved from storage, it must be cached using an LRUCache object.

For the client (in this case, the Solution class), using CachingProxyRetriever should be no different than using the OriginalRetriever class.

P.S. You will need LRUCache and OriginalRetriever fields in the CachingProxyRetriever class.

Requirements:

An OriginalRetriever field must be created in the CachingProxyRetriever class.
An LRUCache field must be created in the CachingProxyRetriever class.
The CachingProxyRetriever class's constructor must accept one Storage argument and initialize an OriginalRetriever field.
The CachingProxyRetriever class's retrieve method must use the find method to search the cache for a suitable object.
The CachingProxyRetriever class's retrieve method must retrieve the object from storage using an OriginalRetriever object's retrieve method and add it to the cache if it isn't found there.
The CachingProxyRetriever class's retrieve method must not call the OriginalRetriever's retrieve method if the object is found in the cache.
The CachingProxyRetriever class's retrieve method must return from storage the object that corresponds to the id passed as an argument.
The CachingProxyRetriever class must support the Retriever interface.

package com.codegym.task.task37.task3708; import com.codegym.task.task37.task3708.retrievers.OriginalRetriever; import com.codegym.task.task37.task3708.retrievers.Retriever; import com.codegym.task.task37.task3708.storage.RemoteStorage; import com.codegym.task.task37.task3708.storage.Storage; import com.codegym.task.task37.task3708.retrievers.CachingProxyRetriever; /* Caching proxy */ public class Solution { private static final int n = 10; public static void main(String[] args) { Storage storage = new RemoteStorage(); fillStorage(storage); System.out.println("Testing OriginalRetriever: "); testRetriever(new OriginalRetriever(storage)); System.out.println("\n\n\n\n\n\n\n\n\n\nTesting CachingProxyRetriever: "); testRetriever(new CachingProxyRetriever(storage)); } private static void fillStorage(Storage storage) { for (int i = 0; i < n; i++) { storage.add("Resource #" + i); } } private static void testRetriever(Retriever retriever) { for (int i = 0; i < n * 4; i++) { System.out.println("Loaded value : " + retriever.retrieve((long) (Math.random() * n))); } } }

Comments (3)

Popular
New
Old

You must be signed in to leave a comment

JianQiu Hwang

Level 35 , Washington

10 May 2020, 03:57

solution

You should initialize the lruCache, that is, change line 8 in `CachingProxyRetriever` to

public LRUCache<Long, Object> lruCache = new LRUCache<>(100);

Wei Cui

Level 39 , Newark, United States

22 April 2020, 03:10

public class CachingProxyRetriever implements Retriever{
    private Storage storage;
    private OriginalRetriever originalRetriever;
    private LRUCache<Long, Object> lruCache;

    public CachingProxyRetriever(Storage storage) {
        this.storage = storage;
        this.originalRetriever = new OriginalRetriever(storage);
        lruCache = new LRUCache<>(16);
    }


    public Object retrieve(long id) {
        Object obj = lruCache.find(id);
        if (obj == null) {
            obj = originalRetriever.retrieve(id);
            lruCache.set(id, obj);
        }
        return obj;
    }
}

matemate123

Level 50 , Kraków, Poland

28 October 2023, 09:20

Line 2 and 7 are unnecessary. I did the same but this.originalRetriever = new OriginalRetriever(storage); use "storage" directly in constructor, then initialize Storage storage is not used.