【问题】ArrayList扩容机制为啥是1.5倍+1？

关注。跟hash同理？ 【 在 workingloong 的大作中提到: 】 : Java ArrayList扩容机制是1.5倍+1，最近面试被问为啥选取1.5倍，而不是2倍或者其他的？ : 发自「贵邮」

cpp vector是2倍

int newCapacity = oldCapacity + (oldCapacity >> 1); 因为比特操作快！我猜的。我去谷歌一下

保证最大浪费最小 发自「贵邮」

这是以前程序员得出的经验值 【 在 workingloong (workingloong) 的大作中提到: 】 : Java ArrayList扩容机制是1.5倍+1，最近面试被问为啥选取1.5倍，而不是2倍或者其他的？ : --

The harm is that the bigger the size of the ArrayList, the more memory allocated to it (which could go to waste if the space is not used). Since increasing the capacity of the ArrayList is much less expensive than increasing the capacity of a HashMap, it makes sense to be more conservative with the increase of capacity of an ArrayList. 就是说，ArrList的扩容消费相对HashMap更小，所以允许ArrList更频繁的扩容。

赞~ 【 在 Sluggard (Sluggard) 的大作中提到: 】 : The harm is that the bigger the size of the ArrayList, the more memory allocated... : 就是说，ArrList的扩容消费相对HashMap更小，所以允许ArrList更频繁的扩容。

赞，干货！ 【 在 Sluggard (Sluggard) 的大作中提到: 】 : The harm is that the bigger the size of the ArrayList, the more memory allocated to it (which could go to waste if the space is not used). Since increasing the capacity of the ArrayList is much less expensive than increasing the capacity of a HashMap, it makes sense to be more conservative with the increase of capacity of an ArrayList. : 就是说，ArrList的扩容消费相对HashMap更小，所以允许ArrList更频繁的扩容。 通过『我邮2.0』发布

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