Java基於數組實現的LRU緩存

public class LRUBasedArray<T> {

    private static final int DEFAULT_CAPACITY = (1 << 3);

    private int capacity;

    private int count;

    private T[] value;

    private Map<T, Integer> holder;

    public LRUBasedArray() {
        this(DEFAULT_CAPACITY);
    }

    public LRUBasedArray(int capacity) {
        this.capacity = capacity;
        value = (T[]) new Object[capacity];
        count = 0;
        holder = new HashMap<T, Integer>(capacity);
    }

    /**
     * 模擬訪問某個值
     * @param object
     */
    public void offer(T object) {
        if (object == null) {
            throw new IllegalArgumentException("該緩存容器不支持null!");
        }
        Integer index = holder.get(object);
        if (index == null) {
            if (isFull()) {
                removeAndCache(object);
            } else {
                cache(object, count);
            }
        } else {
            update(index);
        }
    }

    /**
     * 若緩存中有指定的值，則更新位置
     * @param end
     */
    public void update(int end) {
        T target = value[end];
        rightShift(end);
        value[0] = target;
        holder.put(target, 0);
    }

    /**
     * 緩存數據到頭部，但要先右移
     * @param object
     * @param end 數組右移的邊界
     */
    public void cache(T object, int end) {
        rightShift(end);
        value[0] = object;
        holder.put(object, 0);
        count++;
    }

    /**
     * 緩存滿的情況，踢出後，再緩存到數組頭部
     * @param object
     */
    public void removeAndCache(T object) {
        T key = value[--count];
        holder.remove(key);
        cache(object, count);
    }

    /**
     * end左邊的數據統一右移一位
     * @param end
     */
    private void rightShift(int end) {
        for (int i = end - 1; i >= 0; i--) {
            value[i + 1] = value[i];
            holder.put(value[i], i + 1);
        }
    }

    public boolean isContain(T object) {
        return holder.containsKey(object);
    }

    public boolean isEmpty() {
        return count == 0;
    }

    public boolean isFull() {
        return count == capacity;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < count; i++) {
            sb.append(value[i]);
            sb.append(" ");
        }
        return sb.toString();
    }

    static class TestLRUBasedArray {

        public static void main(String[] args) {
            testDefaultConstructor();
            testSpecifiedConstructor(4);
//            testWithException();
        }

        private static void testWithException() {
            LRUBasedArray<Integer> lru = new LRUBasedArray<Integer>();
            lru.offer(null);
        }

       
    }
}