Implementing an LRU cache

You're developing a web application that frequently retrieves user profile information as strings. To improve performance, you want to implement a simple cache that stores these profile strings and can identify which entries were least recently used.

The CacheEntry class was preloaded for you.

Este exercício faz parte do curso

Optimizing Code in Java

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Instruções do exercício

In the get() method, retrieve the cache entry for the specified key.
After retrieving the key, update its access time.
After putting an entry in the cache, if the capacity has been exceeded, remove the least recently used entry.

Exercício interativo prático

Experimente este exercício completando este código de exemplo.

public class StringCache {
    private final int capacity = 100;
    private final Map cache = new HashMap<>();
    
    public String get(String key) {
        // Get the entry for the specified key
        CacheEntry entry = ____.get(____);
        if (entry == null) return null;
        // Update its access time
        entry.____();
        return entry.value;
    }
    
    public void put(String key, String value) {
        cache.put(key, new CacheEntry(value));
        if (cache.size() > capacity) {
            // If capacity exceeded, remove least recently used
            ____();
        }
    }

    void removeLeastRecentlyUsed() {
        String lruKey = null;
        long oldest = Long.MAX_VALUE;
        for (Map.Entry e : cache.entrySet()) {
            if (e.getValue().lastAccessed < oldest) {
                oldest = e.getValue().lastAccessed;
                lruKey = e.getKey();
            }
        }
        if (lruKey != null) { cache.remove(lruKey); }
    }

    public static void main(String[] args) {}
}

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