1、arraylist
默认大小为10
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/** * default initial capacity. */ private static final int default_capacity = 10 ; |
最大容量为2^30 - 8
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/** * 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
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/** * 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
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/** * 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
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/** * 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
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/** * 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); } |
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原文链接：https://blog.csdn.net/u012099869/article/details/50411767
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