ArrayList及HashMap的扩容规则讲解
1、ArrayList
创新互联建站服务项目包括清涧网站建设、清涧网站制作、清涧网页制作以及清涧网络营销策划等。多年来,我们专注于互联网行业,利用自身积累的技术优势、行业经验、深度合作伙伴关系等,向广大中小型企业、政府机构等提供互联网行业的解决方案,清涧网站推广取得了明显的社会效益与经济效益。目前,我们服务的客户以成都为中心已经辐射到清涧省份的部分城市,未来相信会继续扩大服务区域并继续获得客户的支持与信任!
默认大小为10
/** * Default initial capacity. */ private static final int DEFAULT_CAPACITY = 10;
最大容量为2^30 - 8
/** * The maximum size of array to allocate. * Some VMs reserve some header words in an array. * Attempts to allocate larger arrays may result in * OutOfMemoryError: Requested array size exceeds VM limit */ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; /** * A constant holding the maximum value an {@code int} can * have, 231-1. */ public static final int MAX_VALUE = 0x7fffffff;
扩容规则为:oldCapacity*1.5
/** * Increases the capacity to ensure that it can hold at least the * number of elements specified by the minimum capacity argument. * @param minCapacity the desired minimum capacity */ private void grow(int minCapacity) { // overflow-conscious code int oldCapacity = elementData.length; int newCapacity = oldCapacity + (oldCapacity >> 1); if (newCapacity - minCapacity < 0) newCapacity = minCapacity; if (newCapacity - MAX_ARRAY_SIZE > 0) newCapacity = hugeCapacity(minCapacity); // minCapacity is usually close to size, so this is a win: elementData = Arrays.copyOf(elementData, newCapacity); }
2、HashMap
默认大小: 16
/** * The default initial capacity - MUST be a power of two. */ static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
最大容量为:2^30
/** * The maximum capacity, used if a higher value is implicitly specified * by either of the constructors with arguments. * MUST be a power of two <= 1<<30. */ static final int MAXIMUM_CAPACITY = 1 << 30;
扩容规则为:大于oldCapacity的最小的2的n次方整数
/** * Adds a new entry with the specified key, value and hash code to * the specified bucket. It is the responsibility of this * method to resize the table if appropriate. * Subclass overrides this to alter the behavior of put method. */ void addEntry(int hash, K key, V value, int bucketIndex) { if ((size >= threshold) && (null != table[bucketIndex])) { resize(2 * table.length); hash = (null != key) ? hash(key) : 0; bucketIndex = indexFor(hash, table.length); } createEntry(hash, key, value, bucketIndex); }
总结
以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,谢谢大家对创新互联的支持。如果你想了解更多相关内容请查看下面相关链接
网页题目:ArrayList及HashMap的扩容规则讲解
链接URL:http://lswzjz.com/article/jdedgj.html