如何对Java Hashtable进行排序? [英] How to sort a Java Hashtable?

问题描述

我在Java Hashtable中插入了一些数据.如果我从哈希表读取数据，则返回的顺序与插入时的顺序不同.如何从哈希表中获取排序的数据?

I inserted some data into a Java Hashtable. If I read the data from the Hashtable it doesn't come back in the same order that I inserted it in. How do I get the ordered data from the Hashtable?

我使用以下代码从哈希表中获取值:

I use the following code to get the values from the hashtable:

// Get a set of the entries
Set set = hsUpdateValues.entrySet();
// Get an iterator
Iterator i = set.iterator();
// Display elements
while (i.hasNext()) {
    Map.Entry me = (Map.Entry) i.next();            
    System.out.print(
        "Key : " + me.getKey()
        + ", Value: " + me.getValue()
    );
}

推荐答案

如果您想要保留订单的地图，则应使用

If you want an order-preserving map, you should use LinkedHashMap:

Map接口的哈希表和链表实现，具有可预测的迭代顺序.此实现与HashMap的不同之处在于，它维护一个贯穿其所有条目的双向链接列表.此链表定义了迭代顺序，通常是将键插入映射的顺序(插入顺序).请注意，如果将密钥重新插入到映射中，则插入顺序不会受到影响. (如果在调用前m.containsKey(k)返回true时调用了m.put(k, v)，则将键k重新插入到映射m中.)

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order). Note that insertion order is not affected if a key is re-inserted into the map. (A key k is reinserted into a map m if m.put(k, v) is invoked when m.containsKey(k) would return true immediately prior to the invocation.)

此实现使客户免于HashMap(和Hashtable)提供的未指定的，通常混乱的排序，而不会导致与TreeMap相关的成本增加.

This implementation spares its clients from the unspecified, generally chaotic ordering provided by HashMap (and Hashtable), without incurring the increased cost associated with TreeMap.

请注意，通常将它与HashMap而不是Hashtable进行比较-我不知道与Hashtable保持顺序的等价物；不管怎么说，后者现在通常都不会使用(就像ArrayList通常优先于Vector一样使用).

Note that this is usually compared with HashMap rather than Hashtable - I don't know of an order-preserving equivalent to Hashtable; the latter isn't usually used these days anyway (just as ArrayList is usually used in preference to Vector).

我假设您想要的是插入顺序，而不是键排序顺序.如果需要后者，请使用 TreeMap .

I've assumed you want insertion order rather than key-sorted order. If you want the latter, use TreeMap.

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