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。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

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(...

问在Java中将数据追加到地图
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Java中将数据追加到地图EN