Question

测试testGetBucket（）仅在密钥大于5个字符时才起作用。例如，如果任何小狗名称超过5个字符，测试将返回getBucket方法的ArrayIndexOutOfBounds异常。

@Test
    public void testGetBucket() {
        List<Puppy> puppies = getPuppies();
        MyHashTable<String, Puppy> instance = new MyHashTable<>(DefaultCapacity, DefaultLoadFactor);

        for (int i = 0; i < 10; i++) {
            Puppy puppy = puppies.get(i);
            instance.put(puppy.name, puppy);
            System.out.print(i);
        }

        List<KeyValuePair<String, Puppy>> actual = instance.getBucket(8);
        assertEquals("Size of bucket is three", 3, actual.size());
        for (int i = 0; i < actual.size(); i++) {
            KeyValuePair<String, Puppy> p = actual.get(i);
            if (p.key.equals("Bob")) {
                assertEquals("Bucket contains " + p.value.name, puppies.get(1), p.value);
            } else if (p.key.equals("Francois")) {
                assertEquals("Bucket contains " + p.value.name, puppies.get(5), p.value);
            } else if (p.key.equals("Inigo")) {
                assertEquals("Bucket contains " + p.value.name, puppies.get(8), p.value);
            }
        }

        actual = instance.getBucket(3);
        assertEquals("Size of bucket is Zero", 0, actual.size());

        actual = instance.getBucket(0);
        assertEquals("Size of bucket is 1", 1, actual.size());
        KeyValuePair<String, Puppy> p = actual.get(0);
        assertEquals("Bucket contains " + p.value.name, puppies.get(2), p.value);
    }



public void put(K key, V value)
    {
       remove(key);
       KeyValuePair<K,V> element = new KeyValuePair<K,V>(key, value);
       getBucket(getBucketIndex(key.hashCode())).add(element);
    }


public int getBucketIndex(int hashCode)
    {
        return hashCode % getNumberOfCollisionBuckets();
    }

public List<KeyValuePair<K,V>> getBucket(int bucketIndex)
    {

        return collisionBuckets[bucketIndex];
    }

Answer 1

我会在这里继续说问题就是这部分

return hashCode % getNumberOfCollisionBuckets();

如果您的命名是任何指导，则问题是hashCode。我不知道你为什么决定采用如此脆弱的实施方式。

当您的错误发生时，hashCode必须是一个值，该值会在调制后产生高于数组索引值的结果。

那么解决这个问题的方法呢？停止依赖hashCode来做一些像获取数组索引......这不是它的目的。

奇怪的HashTable ArrayIndexOutOfBounds异常

1 个答案: