java/w8/Cache.java

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

public class Cache<K, V> {
    private final int capacity;
    private final Map<K, V> cache;

    public Cache(int capacity) {
        this.capacity = capacity;
        this.cache = new HashMap<>();
    }

    public void put(K key, V value) {
        if (key == null) {
            return;
        }
        if (cache.size() >= capacity && !cache.containsKey(key)) {
            K oldestKey = cache.keySet().iterator().next();
            cache.remove(oldestKey);
        }
        cache.put(key, value);
    }

    public V get(K key) {
        return cache.get(key);
    }

    public void remove(K key) {
        cache.remove(key);
    }

    public void clear() {
        cache.clear();
    }

    public int getCapacity() {
        return capacity;
    }

    public int getSize() {
        return cache.size();
    }

    public boolean containsKey(K key) {
        return cache.containsKey(key);
    }

    @SuppressWarnings("unchecked")
    public Class<K> getKeyType() {
        Type type = getClass().getGenericSuperclass();
        if (type instanceof ParameterizedType) {
            ParameterizedType paramType = (ParameterizedType) type;
            Type[] typeArgs = paramType.getActualTypeArguments();
            if (typeArgs != null && typeArgs.length > 0 && typeArgs[0] instanceof Class) {
                return (Class<K>) typeArgs[0];
            }
        }
        return null;
    }

    @SuppressWarnings("unchecked")
    public Class<V> getValueType() {
        Type type = getClass().getGenericSuperclass();
        if (type instanceof ParameterizedType) {
            ParameterizedType paramType = (ParameterizedType) type;
            Type[] typeArgs = paramType.getActualTypeArguments();
            if (typeArgs != null && typeArgs.length > 1 && typeArgs[1] instanceof Class) {
                return (Class<V>) typeArgs[1];
            }
        }
        return null;
    }

    @Override
    public String toString() {
        return "Cache{" +
                "capacity=" + capacity +
                ", cache=" + cache +
                '}';
    }
}