java集合转换慢
IMap<Long, Vehicle> mapVehicles = // get all vehicles , total 2500 unit
Collection<Vehicle> collectionVeh = mapVehicles.values(); // fast
// I want to sort it so wrap to ArrayList
List<Vehicle> listVehicle = new ArrayList(collectionVeh .values()); // very slow
Collections.sort(listVehicle );// fast
如何快速将集合转换为列表？
谢谢。
IMap<Long, Vehicle> mapVehicles = // get all vehicles , total 2500 unit
Collection<Vehicle> collectionVeh = mapVehicles.values(); // fast
// I want to sort it so wrap to ArrayList
List<Vehicle> listVehicle = new ArrayList(collectionVeh .values()); // very slow
Collections.sort(listVehicle );// fast
How can i convert Collection to List very fastly ?
Thanks.
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如果您的
Collection不是List，并且您希望将其作为List，那么没有比执行某些操作更快的方法了就像new ArrayList(yourCollection)。 （可以这么说，我不认为构造函数会执行任何您可以跳过的不必要的工作。）但是您可以做的是更改原始集合。如果它当前是一个
HashMap，那么您的迭代所花费的时间将与其容量成正比。通过更改为LinkedHashMap，您可以按与其大小成比例的时间对其进行迭代。 （可能差异可以忽略不计，但值得一试。）If you have a
Collectionthat's not aList, and you want to have it as aList, there is no faster way than to do something likenew ArrayList(yourCollection). (I don't believe that constructor does any unnecessary work that you could skip, so to speak.)What you could do however is to change the original collection. If it's currently a
HashMapyour iteration will take time proportional to it's capacity. By changing to aLinkedHashMapyou can iterate over it in time proportional to it's size. (Probably a negligible difference, but it could be worth a try.)如果将车辆放入 TreeSet 中会更快吗？
Is it faster if you drop the vehicles in a TreeSet instead?
您可以尝试
Arrays.asList(collectionVeh.values().toArray)吗？也许它会跑得更快？Could you please try
Arrays.asList(collectionVeh.values().toArray)? May be it will run faster?