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, 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

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