ArrayList及HashMap的扩容规则讲解
更新时间:2019年02月12日 16:23:39 作者:wlmmmm
今天小编就为大家分享一篇关于ArrayList及HashMap的扩容规则讲解,小编觉得内容挺不错的,现在分享给大家,具有很好的参考价值,需要的朋友一起跟随小编来看看吧
1、ArrayList
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, 2<sup>31</sup>-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,谢谢大家对脚本之家的支持。如果你想了解更多相关内容请查看下面相关链接
相关文章
SpringBoot整合Mybatis实现商品评分的项目实践
本文介绍了SpringBoot整合Mybatis-plus框架实现对商品评分的功能实现流程和前端接口实现过程,文中通过示例代码介绍的非常详细,需要的朋友们下面随着小编来一起学习学习吧2024-02-02Shiro + JWT + SpringBoot应用示例代码详解
这篇文章主要介绍了Shiro (Shiro + JWT + SpringBoot应用),本文通过实例代码给大家介绍的非常详细,对大家的学习或工作具有一定的参考借鉴价值,需要的朋友可以参考下2020-06-06SpringBoot深入探究@Conditional条件装配的使用
这篇文章主要为大家介绍了SpringBoot底层注解@Conditional的使用分析,有需要的朋友可以借鉴参考下,希望能够有所帮助,祝大家多多进步,早日升职加薪2022-06-06详解Spring/Spring boot异步任务编程WebAsyncTask
这篇文章主要介绍了详解Spring/Spring boot异步任务编程WebAsyncTask,小编觉得挺不错的,现在分享给大家,也给大家做个参考。一起跟随小编过来看看吧2018-06-06
最新评论