entityMap|0|type|LINK|mutability|MUTABLE|data|url|http://docs.oracle.com/javase/1.4.2/docs/api/java/util/List.html#contains%2528java.lang.Object%2529|blocks|key|136321|text|交集使用的是contains，它使用的是equals。你应该在你想做交集的类上实现equals()方法。|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|136322|我没有找到关于set.addAll()实现的具体注释，但它很可能还使用equals()来确定对象是否已经在集合中。|136323|如果你想只比较一个字段，你的equals()应该只比较这个字段。|136324^0|15|8|6|8|0|0|7|C|Z|8|0|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|R|G|@$H|S|I|T|J|K]]|L|@$H|U|I|V|A|W]]|6|$]]|$A|M|C|N|2|E|F|X|G|@$H|Y|I|Z|J|K]|$H|10|I|11|J|K]]|L|@]|6|$]]|$A|O|C|P|2|E|F|12|G|@]|L|@]|6|$]]|$A|Q|C|-4|2|E|F|13|G|@]|L|@]|6|$]]]]

Intersection is using <a href="http://docs.oracle.com/javase/1.4.2/docs/api/java/util/List.html#contains%28java.lang.Object%29" rel="nofollow" title="contains">contains</a>, which uses equals. You should implement <code>equals()</code> method on the class that you want to do intersection.

I didn't find specific comments about <code>set.addAll()</code> implementation, but most probably it also uses <code>equals()</code> to determine if an object is already on the set.

If you want to compare only by a field, your equals() should only compare this field.

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://stackoverflow.com/questions/5283047/intersection-union-of-arraylists-in-java/5283079#5283079|1|http://docs.oracle.com/javase/7/docs/api/java/util/Collection.html|blocks|key|744126|text|与在this+answer中一样，使用交集方法retainAll(Collection)-+Collection和#addAll(Collection)-+union。|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|744127|由于这些方法使用equals，因此您还必须覆盖类中的equals方法，并实现基于单属性的比较。|744128|如果这是一个简单的比较，这里有一个例子(由我的想法生成)：|744129|public+class+Main+{

private+Integer+age;

...

@Override
public+boolean+equals(Object+o)+{
++++if+(this+==+o)+return+true;
++++if+(o+==+null+%7C%7C+getClass()+!=+o.getClass())+return+false;

++++Main+main+=+(Main)+o;

++++if+(age+!=+null+?+!age.equals(main.age)+:+main.age+!=+null)+return+false;

++++return+true;
}|code-block|syntax|javascript|744130^0|N|L|1L|J|2|B|0|1A|A|1|0|Q|6|0|0|0^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|3|4|5|6|$7|A]]]|B|@$C|D|E|F|2|G|H|Y|I|@$J|Z|K|10|L|M]|$J|11|K|12|L|M]]|N|@$J|13|K|14|C|15]|$J|16|K|17|C|18]]|6|$]]|$C|O|E|P|2|G|H|19|I|@$J|1A|K|1B|L|M]]|N|@]|6|$]]|$C|Q|E|R|2|G|H|1C|I|@]|N|@]|6|$]]|$C|S|E|T|2|U|H|1D|I|@]|N|@]|6|$V|W]]|$C|X|E|-4|2|G|H|1E|I|@]|N|@]|6|$]]]]

As in <a href="https://stackoverflow.com/questions/5283047/intersection-union-of-arraylists-in-java/5283079#5283079">this answer</a>, use <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Collection.html" rel="nofollow noreferrer">Collection</a> methods <code>retainAll(Collection)</code>- intersection and <code>#addAll(Collection)</code>- union.

Since those methods use equals, you also have to override <code>equals</code> method in your Class and implement one-property based comparison. 

In case it's simple comparison, here's an example (generated by my IDEA):

<pre><code>public class Main {

private Integer age;

...

@Override
public boolean equals(Object o) {
 if (this == o) return true;
 if (o == null || getClass() != o.getClass()) return false;

 Main main = (Main) o;

 if (age != null ? !age.equals(main.age) : main.age != null) return false;

 return true;
}
</code></pre>

entityMap|blocks|key|4094409|text|Google+Guava有包含这些方法和更多方法的集合类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4094410^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|D|9|@]|A|@]|B|$]]|$2|C|4|-4|6|7|8|E|9|@]|A|@]|B|$]]]]

Google Guava, has Sets class which contains these methods and many more.

entityMap|blocks|key|4094459|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4094460|，但是我想以某种方式覆盖它们，这样它就不会添加一个对象，如果我的集合中已经有一个对象，在选定的property.If中有相同的值，我不太清楚，告诉我，这样我就可以写一个例子。|blockquote|4094461|4094462|4094463|我认为最好的方法是使用ConcurrentMap。|4094464|ConcurrentMap<String,+MyType>+map+=+new+ConcurrentHashMap<>();

//+the+collection+to+retain.
for(MyType+mt:+retainedSet)+map.put(mt.getKey(),+mt);

//+the+collection+to+keep+if+not+duplicated
for(MyType+mt:+onlyIfNewSet)+map.putIfAbsent(mt.getKey(),+mt);

//+to+get+the+intersection.
Set<String>+toKeep+=+new+HashSet<>();
for(MyType+mt:+onlyIfNewSet)+toKeep.add(mt.getKey());

//+keep+only+the+keys+which+match.
map.keySet().retainAll(toKeep);|code-block|syntax|javascript|4094465^0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|-4|5|6|7|O|8|@]|9|@]|A|$]]|$2|B|4|C|5|D|7|P|8|@]|9|@]|A|$]]|$2|E|4|-4|5|6|7|Q|8|@]|9|@]|A|$]]|$2|F|4|-4|5|6|7|R|8|@]|9|@]|A|$]]|$2|G|4|H|5|6|7|S|8|@]|9|@]|A|$]]|$2|I|4|J|5|K|7|T|8|@]|9|@]|A|$L|M]]|$2|N|4|-4|5|6|7|U|8|@]|9|@]|A|$]]]]

<blockquote>
 But I want to override them somehow so that it wont add an object if there's an object already in my set that has the same value in a selected property.If i'm not clear enough tell me so i can write an example.
</blockquote>

I think the best way to do this is to use a ConcurrentMap.

<pre><code>ConcurrentMap&lt;String, MyType&gt; map = new ConcurrentHashMap&lt;&gt;();

// the collection to retain.
for(MyType mt: retainedSet) map.put(mt.getKey(), mt);

// the collection to keep if not duplicated
for(MyType mt: onlyIfNewSet) map.putIfAbsent(mt.getKey(), mt);

// to get the intersection.
Set&lt;String&gt; toKeep = new HashSet&lt;&gt;();
for(MyType mt: onlyIfNewSet) toKeep.add(mt.getKey());

// keep only the keys which match.
map.keySet().retainAll(toKeep);
</code></pre>

hi i've seen this <a href="https://stackoverflow.com/questions/5283047/intersection-union-of-arraylists-in-java">post</a> how to implement the union and intersection when it you have two sets of data,that are strings.how can i do the same when my sets contain objects,and i want to get the union of only one property of each object?

how can I implement the union and intersection of set theory with sets of objects

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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大家好，我看过这个，当你有两组数据时，如何实现并集和交集，也就是strings.how，当我的数据集包含对象时，我能做同样的事情吗？，我只想得到每个对象的一个属性的并集？

问如何实现集合论与对象集的并集和交集？
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问如何实现集合论与对象集的并集和交集？EN