blocks|key|407437|text|因为Map不包含任何重复的键，所以您可以只使用qsnMap.size()来获取唯一键的计数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|407438|entityMap^0|2|3|N|D|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

As a <code>Map</code> does not contain any duplicate keys you can just use <code>qsnMap.size()</code> to get the count of unique keys.

blocks|key|407406|text|Map的基本约定是it+‘t+allow+duplicate+keys。因此，默认情况下地图中的所有keys都是唯一的|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|407407|这是因为Map使用Set来保存键，而Set不允许重复元素|407408|Set的javadoc说|407409|407410|包含不重复的元素的集合。更正式地说，集合不包含e1.equals(+e2+)这样的元素e1和e2对，并且最多包含一个空元素。顾名思义，此接口对数学集合抽象进行建模|blockquote|407411|407412|407413|。|407414|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/6/docs/api/java/util/Set.html^0|0|3|1E|4|C|2|L|E|0|4|3|9|3|I|3|9|3|0|0|0|3|0|0|2|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|D]|$9|17|A|18|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|E|@$9|1G|A|1H|1|1I]]|F|$]]|$1|I|3|J|5|6|7|1J|8|@$9|1K|A|1L|B|C]]|E|@]|F|$]]|$1|K|3|-4|5|6|7|1M|8|@]|E|@]|F|$]]|$1|L|3|M|5|N|7|1N|8|@$9|1O|A|1P|B|D]]|E|@]|F|$]]|$1|O|3|-4|5|6|7|1Q|8|@]|E|@]|F|$]]|$1|P|3|-4|5|6|7|1R|8|@]|E|@]|F|$]]|$1|Q|3|R|5|6|7|1S|8|@]|E|@]|F|$]]|$1|S|3|-4|5|6|7|1T|8|@]|E|@]|F|$]]]|T|$U|$5|V|W|X|F|$Y|Z]]]]

The basic contract of <code>Map</code> is it doesn't allow duplicate keys. So all the <code>keys</code> in the map are by default unique

This is because a <code>Map</code> uses <code><a href="http://docs.oracle.com/javase/6/docs/api/java/util/Set.html" rel="nofollow">Set</a></code> to hold keys and <code>Set</code> doesn't allow duplicate elements

The javadoc for <code>Set</code> says

<blockquote>
 A collection that contains no duplicate elements. More formally, sets
 contain no pair of elements e1 and e2 such that e1.equals(e2), and at
 most one null element. As implied by its name, this interface models
 the mathematical set abstraction
</blockquote>

.

blocks|key|2722549|text|文档说，如果您尝试将新值与已在映射中的键放在一起，它将用新值替换新值，并返回旧值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2722550|因此，如果您想知道键值对的大小/长度/数量，可以通过以下命令找到|2722551|mapObject.size();|code-block|syntax|javascript|2722552|来自oracle+docs>>|2722553|public+V+put(K密钥，V值)将指定值与此映射中的指定密钥关联。如果映射之前包含键的映射，则替换旧值。|2722554|参数：|2722555|+key++-指定值要与之关联的密钥|2722556|+value++-要与指定键关联的值|2722557|返回:返回与key关联的前一个值，如果没有key的映射，则返回null。(+null返回值也可以指示映射以前将null与键关联。)|2722558|entityMap^0|0|15|0|0|0|0|0|K|0|0|3|0|0|5|0|0|7|0|G|8|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|U|3|V|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|W|3|X|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Z|$]]

Docs says, if you try to put new value with a key which is already in map, it will replace the value with the new value and will return old value.

so if you want to know the size/length/numbers of key value pairs, you can find it with

<pre><code>mapObject.size();
</code></pre>

from oracle docs>>

public V put(K key,
 V value)
Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.

Parameters:

key - key with which the specified value is to be associated

value - value to be associated with the specified key 

Returns:
 the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key.)

blocks|key|4188761|text|根据定义，映射中的键是唯一的！Maps不允许使用二进制密钥！|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|4188762|您可以阅读here、here+(德语)、here|4188763|entityMap|0|LINK|mutability|MUTABLE|url|http://openbook.galileodesign.de/javainsel5/javainsel11_005.htm|1|http://www.java-tutorial.org/maps.html|2|http://docs.oracle.com/javase/7/docs/api/java/util/Map.html^0|9|1|0|5|4|0|A|4|1|K|4|2|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@$9|X|A|Y|1|Z]|$9|10|A|11|1|12]|$9|13|A|14|1|15]]|E|$]]|$1|H|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]|R|$5|K|L|M|E|$N|S]]]]

The keys in a map are by definiton unique!
Maps does not allow dublicate keys!

You can read <a href="http://openbook.galileodesign.de/javainsel5/javainsel11_005.htm" rel="nofollow">here</a>, <a href="http://www.java-tutorial.org/maps.html" rel="nofollow">here</a> (german), <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Map.html" rel="nofollow">here</a>

blocks|key|4188607|text|map中的所有键都是唯一的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4188608|所以|4188609|Set+keySet+=+map.keySet();
keySet.size();++//this+is+count+of+keys|code-block|syntax|javascript|4188610|并且集合的大小是计数。|4188611|或者简单地说，map.size()就是你的键数。|offset|length|style|CODE|4188612|entityMap^0|0|0|0|0|7|A|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

All keys in map are unique.

So 

<pre><code>Set keySet = map.keySet();
keySet.size(); //this is count of keys
</code></pre>

And size of the set is count.

or Simply <code>map.size()</code> is your count of keys.

blocks|key|804308|text|映射始终是唯一的。即使你再把同样的钥匙放进去。旧的密钥将被新的密钥替换。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|804309|请学习如何使用地图。This+link应该是可使用的|offset|length|804310|entityMap|0|LINK|mutability|MUTABLE|url|http://binarynerd.com/java-tutorials/advanced-java/using-java-hashmaps.html^0|0|A|9|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Map is always unique. Even if u put the same key again. the old key would be replaced by the new one. 

Please learn how to use map. <a href="http://binarynerd.com/java-tutorials/advanced-java/using-java-hashmaps.html" rel="nofollow">This link</a> should be userful

blocks|key|797403|text|您可以从这个http://docs.oracle.com/javase/tutorial/collections/index.html开始。首先要弄清楚基础知识。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|797404|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/tutorial/collections/index.html^0|6|1P|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can start with this <a href="http://docs.oracle.com/javase/tutorial/collections/index.html" rel="nofollow">http://docs.oracle.com/javase/tutorial/collections/index.html</a> . Get the basics clear first.

The code looks like below:

<pre><code>Map&lt;string , list&gt; qsnMap =new hashmap &lt;string , list&gt;;
If(qsnMap !=null){
 Iterator&lt;Map.Entry&lt;string , list&gt;&gt; entries = 
 qsnMap.entrySet().iterator();
 While(entries.hasNext()){
 Map.Entry&lt;string , &gt; entry = entry.next();
 String mapKey = entry.getKey();
 }
}
</code></pre>

Suppose the data appears like this

"123 , abc" "abc" 
"234 , gdd" "gdd" 
"434 , dhd" "dhd" 
"123 , mnb" "mnb" 

Here i want to use the numerics as key and then use a map in the while loop to get the count of unique keys...i.e the count should be 3 for the above data

Hope this is more understandable.

iterating a hashmap to get the count of unique keys

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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代码如下：Map<string , list> qsnMap =new hashmap <string , list>;If(qsnMap !=null){ Iterator<Map.Entry<string , list>> entries = qsnMap.entrySet().iterator(); While(entries.hasNext()){ Map

问迭代hashmap以获取唯一键的计数
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