blocks|key|1608207|text|Java+Map+Class+Reference的第一行：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1608208|1608209|将键映射到值的对象。映射不能包含重复的键；每个键最多只能映射到一个值。|blockquote|1608210|1608211|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|J|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|K|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|L|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|M|8|@]|9|@]|A|$]]]|H|$]]

First line of the Java Map Class Reference:

<blockquote>
 An object that maps keys to values. A
 map cannot contain duplicate keys;
 each key can map to at most one value.
</blockquote>

blocks|key|1608235|text|你需要一个来自Google+Guava的Multimap。使用Guava+Multimap重写示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1608236|ListMultimap<Integer,+Object>+entireData+=+ArrayListMultimap.create();|code-block|syntax|javascript|1608237|entireData.get(key)返回一个List<Object>。putAll不会覆盖旧的键，但会将这些键的值附加到现有值中。这也比自己处理初始化List实例要好得多。|style|CODE|1608238|entityMap|0|LINK|mutability|MUTABLE|url|http://code.google.com/p/guava-libraries/|1|http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Multimap.html^0|7|C|0|K|8|1|0|0|0|J|N|C|10|6|24|4|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]|$A|10|B|11|1|12]]|C|$]]|$1|D|3|E|5|F|7|13|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|14|8|@$A|15|B|16|K|L]|$A|17|B|18|K|L]|$A|19|B|1A|K|L]|$A|1B|B|1C|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

You want a <a href="http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Multimap.html" rel="noreferrer">Multimap</a> from <a href="http://code.google.com/p/guava-libraries/" rel="noreferrer">Google Guava</a>. Rewriting your example with Guava Multimap:

<pre><code>ListMultimap&lt;Integer, Object&gt; entireData = ArrayListMultimap.create();
</code></pre>

<code>entireData.get(key)</code> returns a <code>List&lt;Object&gt;</code>. <code>putAll</code> will not override old keys but will append the values of those keys to the existing values. This is also much nicer than dealing with initializing the <code>List</code> instances yourself.

blocks|key|4181745|text|for+(Integer+key+:+someMoreData.keySet())
{
++++if+(entireData.containsKey(key))
++++{
++++++++entireData.get(key).addAll(someMoreData.get(key));
++++}
++++else
++++{
++++++++entireData.put(key,+someMoreData.get(key));
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4181746|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>for (Integer key : someMoreData.keySet())
{
 if (entireData.containsKey(key))
 {
 entireData.get(key).addAll(someMoreData.get(key));
 }
 else
 {
 entireData.put(key, someMoreData.get(key));
 }
}
</code></pre>

blocks|key|4181781|text|密钥是唯一的。如果someMoreData有一个与entireData中已经存在的键相同的键，则该值，即对象列表将被覆盖。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4181782|但是，您可以在someMoreData中循环并附加entireData中存在的键，如下所示|4181783|+for(Integer+key:+someMoreData.keySet()){
+++++++if(entireData.get(key)!=null)
+++++++++++entireData.get(key).addAll(someMoreData.get(key));
+++++++else
+++++++++++entireData.put(key,someMoreData.get(key));
+}|code-block|syntax|javascript|4181784|entityMap^0|9|C|P|A|0|7|C|P|A|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

Keys are unique. If <code>someMoreData</code> has a key same as already existing key in <code>entireData</code> the value i.e. list of object will be overwritten.

However you can loop in <code>someMoreData</code> and append for keys that exists in <code>entireData</code> like

<pre><code> for(Integer key: someMoreData.keySet()){
 if(entireData.get(key)!=null)
 entireData.get(key).addAll(someMoreData.get(key));
 else
 entireData.put(key,someMoreData.get(key));
 }
</code></pre>

blocks|key|2584834|text|默认情况下，Java+Maps将一个键映射到一个值as+trojanfoe+writes。如果这还不足以满足您的需求，那么您需要一个多映射实现(从一个键映射到一个值集合的映射)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2584835|最流行的版本可以在两个开源框架Google+Guava和Apache+Commons+/+Collections中找到。|2584836|Guava示例：|style|BOLD|2584837|final+Multimap<Integer,+String>+mmap+=
++++Multimaps.newSetMultimap(
++++++++Maps.<Integer,+Collection<String>>+newHashMap(),
++++++++new+Supplier<Set<String>>(){

++++++++++++@Override
++++++++++++public+Set<String>+get(){
++++++++++++++++return+Sets.newHashSet();
++++++++++++}
++++++++});
mmap.put(1,+"foo");
mmap.put(1,+"bar");
System.out.println(mmap.get(1));|code-block|syntax|javascript|2584838|输出：|2584839|2584840|+foo，bar|blockquote|2584841|2584842|2584843|公共集合示例：|2584844|final+MultiMap+mmap+=+new+MultiHashMap();
mmap.put(1,+"foo");
mmap.put(1,+"bar");
System.out.println(mmap.get(1));|2584845|2584846|2584847|+foo，bar|2584848|2584849|2584850|正如您所看到的，Commons+Collections版本要简单得多，但它的功能也较弱，并且在当前版本中不支持Java1.5泛型。所以我会选芭乐。|2584851|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/4613386/appending-data-to-map-in-java/4613401#4613401|1|http://code.google.com/p/guava-libraries/|2|http://commons.apache.org/collections/^0|P|J|0|0|F|C|1|S|S|2|0|0|8|0|0|0|0|0|0|0|0|7|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@$A|1L|B|1M|1|1N]]|C|$]]|$1|D|3|E|5|6|7|1O|8|@]|9|@$A|1P|B|1Q|1|1R]|$A|1S|B|1T|1|1U]]|C|$]]|$1|F|3|G|5|6|7|1V|8|@$A|1W|B|1X|H|I]]|9|@]|C|$]]|$1|J|3|K|5|L|7|1Y|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1Z|8|@]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|20|8|@]|9|@]|C|$]]|$1|R|3|S|5|T|7|21|8|@]|9|@]|C|$]]|$1|U|3|-4|5|6|7|22|8|@]|9|@]|C|$]]|$1|V|3|-4|5|6|7|23|8|@]|9|@]|C|$]]|$1|W|3|X|5|6|7|24|8|@$A|25|B|26|H|I]]|9|@]|C|$]]|$1|Y|3|Z|5|L|7|27|8|@]|9|@]|C|$M|N]]|$1|10|3|P|5|6|7|28|8|@]|9|@]|C|$]]|$1|11|3|-4|5|6|7|29|8|@]|9|@]|C|$]]|$1|12|3|13|5|T|7|2A|8|@]|9|@]|C|$]]|$1|14|3|-4|5|6|7|2B|8|@]|9|@]|C|$]]|$1|15|3|-4|5|6|7|2C|8|@]|9|@]|C|$]]|$1|16|3|17|5|6|7|2D|8|@]|9|@]|C|$]]|$1|18|3|-4|5|6|7|2E|8|@]|9|@]|C|$]]]|19|$1A|$5|1B|1C|1D|C|$1E|1F]]|1G|$5|1B|1C|1D|C|$1E|1H]]|1I|$5|1B|1C|1D|C|$1E|1J]]]]

Per default, Java Maps map one key to one value, <a href="https://stackoverflow.com/questions/4613386/appending-data-to-map-in-java/4613401#4613401">as trojanfoe writes</a>. If that is not sufficient to your needs, you need a Multi-Map implementation (A Map that maps from a key to a collection of values).

The most popular versions can be found in two open source Frameworks, <a href="http://code.google.com/p/guava-libraries/" rel="nofollow noreferrer">Google Guava</a> and <a href="http://commons.apache.org/collections/" rel="nofollow noreferrer">Apache Commons / Collections</a>.

Guava Example:

<pre><code>final Multimap&lt;Integer, String&gt; mmap =
 Multimaps.newSetMultimap(
 Maps.&lt;Integer, Collection&lt;String&gt;&gt; newHashMap(),
 new Supplier&lt;Set&lt;String&gt;&gt;(){

 @Override
 public Set&lt;String&gt; get(){
 return Sets.newHashSet();
 }
 });
mmap.put(1, "foo");
mmap.put(1, "bar");
System.out.println(mmap.get(1));
</code></pre>

Output:

<blockquote>
 [foo, bar]
</blockquote>

Commons Collections Example:

<pre><code>final MultiMap mmap = new MultiHashMap();
mmap.put(1, "foo");
mmap.put(1, "bar");
System.out.println(mmap.get(1));
</code></pre>

Output:

<blockquote>
 [foo, bar]
</blockquote>

As you can see, the Commons Collections version is a lot simpler, but it's also less powerful, and in the current version it doesn't support Java 1.5 generics. So I'd go with Guava.

blocks|key|4181881|text|类似于willcodejavaforfood的“不需要依赖项”的答案，但使用entrySet代替，以减少HashMap检索。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4181882|public+static+<K,V>+void+appendMapBtoMapA(HashMap<K,List<V>>+a,+HashMap<K,List<V>>+b)+{
++++for+(Map.Entry<K,+List<V>>+bEntry+:+b.entrySet())+{
++++++++if+(a.containsKey(bEntry.getKey()))+{
++++++++++++a.get(bEntry.getKey()).addAll(bEntry.getValue());
++++++++}+else+{
++++++++++++a.put(bEntry.getKey(),+bEntry.getValue());
++++++++}
++++}
}|code-block|syntax|javascript|4181883|或者使用entrySet删除contains调用并添加null检查的Nishant|4181884|public+static+<K,V>+void+appendMapBtoMapA(HashMap<K,List<V>>+a,+HashMap<K,List<V>>+b)+{
++++for+(Map.Entry<K,+List<V>>+bEntry+:+b.entrySet())+{
++++++++List<V>+aValue+=+a.get(bEntry.getKey());
++++++++if+(aValue+!=+null)+{
++++++++++++aValue.addAll(bEntry.getValue());
++++++++}+else+{
++++++++++++a.put(bEntry.getKey(),+bEntry.getValue());
++++++++}
++++}
}|4181885|或使用java+8|4181886|public+static+<K,V>+void+appendMapBtoMapA(HashMap<K,List<V>>+a,+HashMap<K,List<V>>+b)+{
++++for+(Map.Entry<K,+List<V>>+bEntry+:+b.entrySet())+{
++++++++a.computeIfAbsent(
++++++++++++bEntry.getKey(),+
++++++++++++k+->+new+LinkedList<>()
++++++++).addAll(bEntry.getValue());
++++}
}|4181887|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/51382/willcodejavaforfood|1|https://stackoverflow.com/users/298455/nishant^0|3|J|0|0|0|Y|7|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|K|3|L|5|F|7|19|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1A|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1B|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

similar to <a href="https://stackoverflow.com/users/51382/willcodejavaforfood">willcodejavaforfood</a>'s no dependencies needed answer but using an entrySet instead for less HashMap retrievals.

<pre><code>public static &lt;K,V&gt; void appendMapBtoMapA(HashMap&lt;K,List&lt;V&gt;&gt; a, HashMap&lt;K,List&lt;V&gt;&gt; b) {
 for (Map.Entry&lt;K, List&lt;V&gt;&gt; bEntry : b.entrySet()) {
 if (a.containsKey(bEntry.getKey())) {
 a.get(bEntry.getKey()).addAll(bEntry.getValue());
 } else {
 a.put(bEntry.getKey(), bEntry.getValue());
 }
 }
}
</code></pre>

or <a href="https://stackoverflow.com/users/298455/nishant">Nishant</a>'s which drops a contains call and adds a null check but with entrySet

<pre><code>public static &lt;K,V&gt; void appendMapBtoMapA(HashMap&lt;K,List&lt;V&gt;&gt; a, HashMap&lt;K,List&lt;V&gt;&gt; b) {
 for (Map.Entry&lt;K, List&lt;V&gt;&gt; bEntry : b.entrySet()) {
 List&lt;V&gt; aValue = a.get(bEntry.getKey());
 if (aValue != null) {
 aValue.addAll(bEntry.getValue());
 } else {
 a.put(bEntry.getKey(), bEntry.getValue());
 }
 }
}
</code></pre>

or with java 8

<pre><code>public static &lt;K,V&gt; void appendMapBtoMapA(HashMap&lt;K,List&lt;V&gt;&gt; a, HashMap&lt;K,List&lt;V&gt;&gt; b) {
 for (Map.Entry&lt;K, List&lt;V&gt;&gt; bEntry : b.entrySet()) {
 a.computeIfAbsent(
 bEntry.getKey(), 
 k -&gt; new LinkedList&lt;&gt;()
 ).addAll(bEntry.getValue());
 }
}
</code></pre>

I have a Map

<pre><code>Map&lt;Integer, List&lt;Object&gt;&gt; entireData;
</code></pre>

Now to this I'm adding some data using putAll like

<pre><code>entireData.putAll(someData);
</code></pre>

where someData returns <code>Map&lt;Integer, List&lt;Object&gt;&gt;</code>

Now, I have another line which says

<pre><code>entireData.putAll(someMoreData);
</code></pre>

which also returns <code>Map&lt;Integer, List&lt;Object&gt;&gt;</code>, but by doing this it over-writes the content of the existing entireData, how do I append?

Appending data to Map in Java

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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我有一张地图Map<Integer, List<Object>> entireData;现在，我使用putAll添加了一些数据，比如entireData.putAll(someData);其中someData返回Map<Integer, List<Object>>现在，我有另一句话说entireData.putAll(someMoreData);这也会返回Map<Integer, List<Obj

问在Java中将数据追加到地图
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回答 6

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