blocks|key|1398617|text|如果您将键/值存储为字符串，则可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1398618|HashMap<String,+String>+newMap+=+new+HashMap<String,+String>();
newMap.put("my_code",+"shhh_secret");
String+value+=+newMap.get("my_code");|code-block|syntax|javascript|1398619|问题是在HashMap+(键和值)中填充了什么|1398620|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you are storing keys/values as strings, then this will work:

<pre><code>HashMap&lt;String, String&gt; newMap = new HashMap&lt;String, String&gt;();
newMap.put("my_code", "shhh_secret");
String value = newMap.get("my_code");
</code></pre>

The question is what gets populated in the HashMap (key &amp; value)

blocks|key|1183245|text|如果您将使用泛型并将地图定义为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183246|Map<String,String>+map+=+new+HashMap<String,String>();|code-block|syntax|javascript|1183247|然后取值为|1183248|+String+s+=+map.get("keyStr");+|1183249|您不需要对map.get()进行类型转换或调用toString方法来获取字符串值|1183250|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If you will use Generics and define your map as 

<pre><code>Map&lt;String,String&gt; map = new HashMap&lt;String,String&gt;();
</code></pre>

then fetching value as 

<pre><code> String s = map.get("keyStr"); 
</code></pre>

you wont be required to typecast the map.get() or call toString method to get String value

blocks|key|1183082|text|你的问题恐怕一点也不清楚。键没有“名称”；就map而言，它不是“调用”任何东西--它只是一个键，并将与其他键进行比较。如果你有很多不同种类的钥匙，我强烈建议你把它们放在不同的地图中，以保持理智。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183083|如果这不起作用，请澄清这个问题-最好是用一些代码来说明你的意思。|1183084|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Your question isn't at all clear I'm afraid. A key doesn't have a "name"; it's not "called" anything as far as the map is concerned - it's just a key, and will be compared with other keys. If you have lots of different kinds of keys, I strongly suggest you put them in different maps for the sake of sanity.

If this doesn't help, please clarify the question - preferrably with some code to show what you mean.

blocks|key|1183092|text|map.get(myCode)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1183093|entityMap^0|0|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

blocks|key|1183286|text|这里需要注意的重要一点是，如果您的key是java中用户定义类的对象，那么一定要覆盖equals方法。因为HashMap.get(对象键)方法使用equals方法来匹配键值。如果您不覆盖equals方法，那么它将尝试简单地根据键的引用而不是键的实际值来查找值，在这种情况下，它将始终返回null。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183287|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

An important point to be noted here is that if your key is an object of user-defined class in java then make it a point to override the equals method. Because the HashMap.get(Object key) method uses the equals method for matching the key value. If you do not override the equals method then it will try to find the value simply based on the reference of the key and not the actual value of key in which case it will always return a null.

blocks|key|1398825|text|假设您将HashMap声明为:-|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1398826|HashMap<Character,Integer>+hs+=+new+HashMap<>();|code-block|syntax|javascript|1398827|然后，map中的键是字符数据类型，值类型为int+type.Now，为了得到键对应的值，不管键的类型，值类型，语法是:-|1398828|++++char+temp+=+'a';
++++if(hs.containsKey(temp)){
`+++++++int+val+=+hs.get(temp);+//val+is+the+value+corresponding+to+key+temp
++++}|1398829|所以，根据你的问题，你想要得到一个新的字符串值，只要声明HashMap为HashMap<“key.For+of+key"，"datatype+of+value”hs+=HashMap<+HashMap<>()；使用这种方法可以使你的代码更整洁，而且你也不必将hs.get("my_code")的结果转换成字符串，因为默认情况下，如果在输入时已经将值保存为字符串，它会返回字符串值。|1398830|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Suppose you declared HashMap as :- 

<pre><code>HashMap&lt;Character,Integer&gt; hs = new HashMap&lt;&gt;();
</code></pre>

Then,key in map is of type Character data type and value of int type.Now,to get value corresponding to key irrespective of type of key,value type, syntax is :-

<pre><code> char temp = 'a';
 if(hs.containsKey(temp)){
` int val = hs.get(temp); //val is the value corresponding to key temp
 }
</code></pre>

So, according to your question you want to get string value corresponding to a key.For this, just declare HashMap as HashMap&lt;"datatype of key","datatype of value" hs = new HashMap&lt;>();
Using this will make your code cleaner and also you don't have to convert the result of hs.get("my_code") to string as by default it returns value of string if at entry time one has kept value as a string.

blocks|key|1183418|text|这是如何使用keySet()、get()、values()和entrySet()函数在映射中获取键和值的另一个示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183419|++++++++Map<Integer,+String>+testKeyset+=+new+HashMap<Integer,+String>();

++++++++testKeyset.put(1,+"first");
++++++++testKeyset.put(2,+"second");
++++++++testKeyset.put(3,+"third");
++++++++testKeyset.put(4,+"fourth");

++++++++//+Print+a+single+value+relevant+to+a+specified+Key.+(uses+keySet())
++++++++for(int+mapKey:+testKeyset.keySet())
++++++++++++System.out.println(testKeyset.get(mapKey));

++++++++//+Print+all+values+regardless+of+the+key.
++++++++for(String+mapVal:+testKeyset.values())
++++++++++++System.out.println(mapVal.trim());

++++++++//+Displays+the+Map+in+Key-Value+pairs+(e.g:+[1=first,+2=second,+3=third,+4=fourth])
++++++++System.out.println(testKeyset.entrySet());|code-block|syntax|javascript|1183420|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is another example of how to use keySet(), get(), values() and entrySet() functions to obtain Keys and Values in a Map:

<pre><code> Map&lt;Integer, String&gt; testKeyset = new HashMap&lt;Integer, String&gt;();

 testKeyset.put(1, "first");
 testKeyset.put(2, "second");
 testKeyset.put(3, "third");
 testKeyset.put(4, "fourth");

 // Print a single value relevant to a specified Key. (uses keySet())
 for(int mapKey: testKeyset.keySet())
 System.out.println(testKeyset.get(mapKey));

 // Print all values regardless of the key.
 for(String mapVal: testKeyset.values())
 System.out.println(mapVal.trim());

 // Displays the Map in Key-Value pairs (e.g: [1=first, 2=second, 3=third, 4=fourth])
 System.out.println(testKeyset.entrySet());
</code></pre>

blocks|key|1183134|text|您可以使用HashMap中的get(对象键)方法。请注意，在许多情况下，您的键类应该覆盖equals方法，才能成为Map键的有用类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183135|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You can use the get(Object key) method from the HashMap.
Be aware that i many cases your Key Class should override the equals method, to be a useful class for a Map key.

blocks|key|1398841|text|+HashMap<Integer,+String>+hmap+=+new+HashMap<Integer,+String>();
+hmap.put(4,+"DD");|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1398842|映射到键4的值为DD|unstyled|offset|length|style|CODE|1398843|entityMap^0|0|4|1|8|2|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]|$G|Q|H|R|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|S|8|@]|9|@]|A|$]]]|L|$]]

<pre><code> HashMap&lt;Integer, String&gt; hmap = new HashMap&lt;Integer, String&gt;();
 hmap.put(4, "DD");
</code></pre>

The Value mapped to Key <code>4</code> is <code>DD</code>

I have a <code>HashMap</code> with various keys and values, how can I get one value out?

I have a key in the map called <code>my_code</code>, it should contain a string, how can I just get that without having to iterate through the map?

So far I've got..

<pre><code> HashMap newMap = new HashMap(paramMap);
 String s = newMap.get("my_code").toString();
</code></pre>

I'm expecting to see a <code>String</code>, such as "ABC" or "DEF" as that is what I put in there initially, but if I do a <code>System.out.println()</code> I get something like <code>java.lang.string#F0454</code>

Sorry, I'm not too familiar with maps as you can probably guess ;)

get string value from HashMap depending on key name

我有一个包含多个键和值的HashMap，如何才能得到一个值呢？我在地图中有一个名为my_code的键，它应该包含一个字符串，我如何才能在不迭代地图的情况下获得它呢？到目前为止我得到了..。   HashMap newMap = new HashMap(paramMap);   String s = newMap.get("my_code").toString();我希望看到一个String，例如"

问根据键名从HashMap获取字符串值
EN

回答 9

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问根据键名从HashMap获取字符串值EN

回答 9

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问根据键名从HashMap获取字符串值
EN