blocks|key|1299016|text|集合本身没有预定义的顺序，因此必须将它们转换为java.util.List。然后，您可以使用一种形式的java.util.Collections.sort|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1299017|Collection<+T+>+collection+=+...;

List<+T+>+list+=+new+ArrayList<+T+>(+collection+);

Collections.sort(+list+);
+//+or
Collections.sort(+list,+new+Comparator<+T+>(+){...}+);

//+list+now+is+sorted|code-block|syntax|javascript|1299018|entityMap^0|N|E|1F|Q|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

Collections by themselves do not have a predefined order, therefore you must convert them to
a <code>java.util.List</code>. Then you can use one form of <code>java.util.Collections.sort</code>

<pre><code>Collection&lt; T &gt; collection = ...;

List&lt; T &gt; list = new ArrayList&lt; T &gt;( collection );

Collections.sort( list );
 // or
Collections.sort( list, new Comparator&lt; T &gt;( ){...} );

// list now is sorted
</code></pre>

blocks|key|1083873|text|Collection没有排序，所以想要对它进行排序是没有意义的。您可以对List实例和数组进行排序，方法是Collections.sort()和Arrays.sort()|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1083874|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/javase/6/docs/api/java/util/Collections.html#sort(java.util.List)|1|http://java.sun.com/javase/6/docs/api/java/util/Arrays.html#sort(java.lang.Object[])^0|0|A|10|4|1H|I|20|D|1H|I|0|20|D|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@$9|Y|A|Z|1|10]|$9|11|A|12|1|13]]|E|$]]|$1|F|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]|N|$5|I|J|K|E|$L|O]]]]

A <code>Collection</code> does not have an ordering, so wanting to sort it does not make sense. You can sort <code>List</code> instances and arrays, and the methods to do that are <a href="http://java.sun.com/javase/6/docs/api/java/util/Collections.html#sort(java.util.List)" rel="noreferrer"><code>Collections.sort()</code></a> and <a href="http://java.sun.com/javase/6/docs/api/java/util/Arrays.html#sort(java.lang.Object[])" rel="noreferrer"><code>Arrays.sort()</code></a>

blocks|key|1299080|text|如果您的集合对象是一个列表，我将使用sort方法，正如其他答案中所建议的那样。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1299081|但是，如果它不是一个列表，并且你并不真正关心返回什么类型的集合对象，我认为创建一个TreeSet比创建一个列表更快：|1299082|TreeSet+sortedSet+=+new+TreeSet(myComparator);
sortedSet.addAll(myCollectionToBeSorted);|code-block|syntax|javascript|1299083|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If your collections object is a list, I would use the sort method, as proposed in the other answers.

However, if it is not a list, and you don't really care about what type of Collection object is returned, I think it is faster to create a TreeSet instead of a List:

<pre><code>TreeSet sortedSet = new TreeSet(myComparator);
sortedSet.addAll(myCollectionToBeSorted);
</code></pre>

blocks|key|1298927|text|如果T是你得到的全部，你就不能。它必须由提供者注入：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1298928|Collection<T+extends+Comparable>|code-block|syntax|javascript|1298929|或在比较器中传递|1298930|Collections.sort(...)|1298931|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You can't if T is all you get. It must be injected by the provider:

<pre><code>Collection&lt;T extends Comparable&gt;
</code></pre>

or pass in the Comparator

<pre><code>Collections.sort(...)
</code></pre>

blocks|key|1298869|text|下面是一个例子。(为了方便起见，我使用了Apache中的CompareToBuilder类，尽管不使用它也可以做到。)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1298870|import+java.util.ArrayList;
import+java.util.Calendar;
import+java.util.Collections;
import+java.util.Comparator;
import+java.util.Date;
import+java.util.HashMap;
import+java.util.List;
import+org.apache.commons.lang.builder.CompareToBuilder;

public+class+Tester+{
++++boolean+ascending+=+true;

++++public+static+void+main(String+args[])+{
++++++++Tester+tester+=+new+Tester();
++++++++tester.printValues();
++++}

++++public+void+printValues()+{
++++++++List<HashMap<String,+Object>>+list+=
++++++++++++new+ArrayList<HashMap<String,+Object>>();
++++++++HashMap<String,+Object>+map+=
++++++++++++new+HashMap<String,+Object>();

++++++++map.put(+"actionId",+new+Integer(1234)+);
++++++++map.put(+"eventId",++new+Integer(21)+++);
++++++++map.put(+"fromDate",+getDate(1)++++++++);
++++++++map.put(+"toDate",+++getDate(7)++++++++);
++++++++list.add(map);

++++++++map+=+new+HashMap<String,+Object>();
++++++++map.put(+"actionId",+new+Integer(456)+);
++++++++map.put(+"eventId",++new+Integer(11)++);
++++++++map.put(+"fromDate",+getDate(1)+++++++);
++++++++map.put(+"toDate",+++getDate(1)+++++++);
++++++++list.add(map);

++++++++map+=+new+HashMap<String,+Object>();
++++++++map.put(+"actionId",+new+Integer(1234)+);
++++++++map.put(+"eventId",++new+Integer(20)+++);
++++++++map.put(+"fromDate",+getDate(4)++++++++);
++++++++map.put(+"toDate",+++getDate(16)+++++++);
++++++++list.add(map);

++++++++map+=+new+HashMap<String,+Object>();
++++++++map.put(+"actionId",+new+Integer(1234)+);
++++++++map.put(+"eventId",++new+Integer(22)+++);
++++++++map.put(+"fromDate",+getDate(8)++++++++);
++++++++map.put(+"toDate",+++getDate(11)+++++++);
++++++++list.add(map);


++++++++map+=+new+HashMap<String,+Object>();
++++++++map.put(+"actionId",+new+Integer(1234)+);
++++++++map.put(+"eventId",++new+Integer(11)+++);
++++++++map.put(+"fromDate",+getDate(1)++++++++);
++++++++map.put(+"toDate",+++getDate(10)+++++++);
++++++++list.add(map);

++++++++map+=+new+HashMap<String,+Object>();
++++++++map.put(+"actionId",+new+Integer(1234)+);
++++++++map.put(+"eventId",++new+Integer(11)+++);
++++++++map.put(+"fromDate",+getDate(4)++++++++);
++++++++map.put(+"toDate",+++getDate(15)+++++++);
++++++++list.add(map);

++++++++map+=+new+HashMap<String,+Object>();
++++++++map.put(+"actionId",+new+Integer(567)+);
++++++++map.put(+"eventId",++new+Integer(12)++);
++++++++map.put(+"fromDate",+getDate(-1)++++++);
++++++++map.put(+"toDate",+++getDate(1)+++++++);
++++++++list.add(map);

++++++++System.out.println("\n+Before+Sorting+\n+");
++++++++for(+int+j+=+0;+j+<+list.size();+j%2B%2B+)
++++++++++++System.out.println(list.get(j));

++++++++Collections.sort(+list,+new+HashMapComparator2()+);

++++++++System.out.println("\n+After+Sorting+\n+");
++++++++for(+int+j+=+0;+j+<+list.size();+j%2B%2B+)
++++++++++++System.out.println(list.get(j));
++++}

++++public+static+Date+getDate(int+days)+{
++++++++Calendar+cal+=+Calendar.getInstance();
++++++++cal.setTime(new+Date());
++++++++cal.add(Calendar.DATE,+days);
++++++++return+cal.getTime();
++++}

++++public+class+HashMapComparator2+implements+Comparator+{
++++++++public+int+compare(Object+object1,+Object+object2)+{
++++++++++++if(+ascending+)+{
++++++++++++++++return+new+CompareToBuilder()
++++++++++++++++++++.append(
++++++++++++++++++++++++((HashMap)object1).get("actionId"),
++++++++++++++++++++++++((HashMap)object2).get("actionId")
++++++++++++++++++++)
++++++++++++++++++++.append(
++++++++++++++++++++++++((HashMap)object2).get("eventId"),
++++++++++++++++++++++++((HashMap)object1).get("eventId")
++++++++++++++++++++)
++++++++++++++++.toComparison();
++++++++++++}+else+{
++++++++++++++++return+new+CompareToBuilder()
++++++++++++++++++++.append(
++++++++++++++++++++++++((HashMap)object2).get("actionId"),
++++++++++++++++++++++++((HashMap)object1).get("actionId")
++++++++++++++++++++)
++++++++++++++++++++.append(
++++++++++++++++++++++++((HashMap)object2).get("eventId"),
++++++++++++++++++++++++((HashMap)object1).get("eventId")
++++++++++++++++++++)
++++++++++++++++.toComparison();
++++++++++++}
++++++++}
++++}
}|code-block|syntax|javascript|1298871|如果你有一个特定的代码，你正在工作，并有问题，你可以张贴你的伪代码，我们可以尝试帮助你！|1298872|entityMap^0|S|G|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Here is an example. (I am using <code>CompareToBuilder</code> class from Apache for convenience, although this can be done without using it.)

<pre><code>import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import org.apache.commons.lang.builder.CompareToBuilder;

public class Tester {
 boolean ascending = true;

 public static void main(String args[]) {
 Tester tester = new Tester();
 tester.printValues();
 }

 public void printValues() {
 List&lt;HashMap&lt;String, Object&gt;&gt; list =
 new ArrayList&lt;HashMap&lt;String, Object&gt;&gt;();
 HashMap&lt;String, Object&gt; map =
 new HashMap&lt;String, Object&gt;();

 map.put( "actionId", new Integer(1234) );
 map.put( "eventId", new Integer(21) );
 map.put( "fromDate", getDate(1) );
 map.put( "toDate", getDate(7) );
 list.add(map);

 map = new HashMap&lt;String, Object&gt;();
 map.put( "actionId", new Integer(456) );
 map.put( "eventId", new Integer(11) );
 map.put( "fromDate", getDate(1) );
 map.put( "toDate", getDate(1) );
 list.add(map);

 map = new HashMap&lt;String, Object&gt;();
 map.put( "actionId", new Integer(1234) );
 map.put( "eventId", new Integer(20) );
 map.put( "fromDate", getDate(4) );
 map.put( "toDate", getDate(16) );
 list.add(map);

 map = new HashMap&lt;String, Object&gt;();
 map.put( "actionId", new Integer(1234) );
 map.put( "eventId", new Integer(22) );
 map.put( "fromDate", getDate(8) );
 map.put( "toDate", getDate(11) );
 list.add(map);


 map = new HashMap&lt;String, Object&gt;();
 map.put( "actionId", new Integer(1234) );
 map.put( "eventId", new Integer(11) );
 map.put( "fromDate", getDate(1) );
 map.put( "toDate", getDate(10) );
 list.add(map);

 map = new HashMap&lt;String, Object&gt;();
 map.put( "actionId", new Integer(1234) );
 map.put( "eventId", new Integer(11) );
 map.put( "fromDate", getDate(4) );
 map.put( "toDate", getDate(15) );
 list.add(map);

 map = new HashMap&lt;String, Object&gt;();
 map.put( "actionId", new Integer(567) );
 map.put( "eventId", new Integer(12) );
 map.put( "fromDate", getDate(-1) );
 map.put( "toDate", getDate(1) );
 list.add(map);

 System.out.println("\n Before Sorting \n ");
 for( int j = 0; j &lt; list.size(); j++ )
 System.out.println(list.get(j));

 Collections.sort( list, new HashMapComparator2() );

 System.out.println("\n After Sorting \n ");
 for( int j = 0; j &lt; list.size(); j++ )
 System.out.println(list.get(j));
 }

 public static Date getDate(int days) {
 Calendar cal = Calendar.getInstance();
 cal.setTime(new Date());
 cal.add(Calendar.DATE, days);
 return cal.getTime();
 }

 public class HashMapComparator2 implements Comparator {
 public int compare(Object object1, Object object2) {
 if( ascending ) {
 return new CompareToBuilder()
 .append(
 ((HashMap)object1).get("actionId"),
 ((HashMap)object2).get("actionId")
 )
 .append(
 ((HashMap)object2).get("eventId"),
 ((HashMap)object1).get("eventId")
 )
 .toComparison();
 } else {
 return new CompareToBuilder()
 .append(
 ((HashMap)object2).get("actionId"),
 ((HashMap)object1).get("actionId")
 )
 .append(
 ((HashMap)object2).get("eventId"),
 ((HashMap)object1).get("eventId")
 )
 .toComparison();
 }
 }
 }
}
</code></pre>

If you have a specific code that you are working on and are having issues, you can post your pseudo code and we can try to help you out!

blocks|key|1299130|text|假设您有一个Person类型的对象列表，使用Lambda表达式，您可以对用户的姓氏进行排序，例如，执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1299131|import+java.util.Arrays;
import+java.util.Collections;
import+java.util.Comparator;
import+java.util.List;

class+Person+{
++++++++private+String+firstName;
++++++++private+String+lastName;

++++++++public+Person(String+firstName,+String+lastName){
++++++++++++this.firstName+=+firstName;
++++++++++++this.lastName+=+lastName;
++++++++}

++++++++public+String+getLastName(){
++++++++++++return+this.lastName;
++++++++}

++++++++public+String+getFirstName(){
++++++++++++return+this.firstName;
++++++++}

++++++++@Override
++++++++public+String+toString(){
++++++++++++return+"Person:+"%2B+this.getFirstName()+%2B+"+"+%2B+this.getLastName();
++++++++}
++++}

++++class+TestSort+{
++++++++public+static+void+main(String[]+args){
++++++++++++List<Person>+people+=+Arrays.asList(
++++++++++++++++++++++++++++++++++new+Person("John",+"Max"),+
++++++++++++++++++++++++++++++++++new+Person("Coolio",+"Doe"),+
++++++++++++++++++++++++++++++++++new+Person("Judith",+"Dan")
++++++++++++);

++++++++++++//Making+use+of+lambda+expression+to+sort+the+collection
++++++++++++people.sort((p1,+p2)->p1.getLastName().compareTo(p2.getLastName()));

++++++++++++//Print+sorted+
++++++++++++printPeople(people);
++++++++}

++++++++public+static+void+printPeople(List<Person>+people){
++++++++++++for(Person+p+:+people){
++++++++++++++++System.out.println(p);
++++++++++++}
++++++++}
++++}|code-block|syntax|javascript|1299132|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|$]]

Assuming you have a list of object of type Person, using Lambda expression, you can sort the last names of users for instance by doing the following: 

<pre><code>import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Person {
 private String firstName;
 private String lastName;

 public Person(String firstName, String lastName){
 this.firstName = firstName;
 this.lastName = lastName;
 }

 public String getLastName(){
 return this.lastName;
 }

 public String getFirstName(){
 return this.firstName;
 }

 @Override
 public String toString(){
 return "Person: "+ this.getFirstName() + " " + this.getLastName();
 }
 }

 class TestSort {
 public static void main(String[] args){
 List&lt;Person&gt; people = Arrays.asList(
 new Person("John", "Max"), 
 new Person("Coolio", "Doe"), 
 new Person("Judith", "Dan")
 );

 //Making use of lambda expression to sort the collection
 people.sort((p1, p2)-&gt;p1.getLastName().compareTo(p2.getLastName()));

 //Print sorted 
 printPeople(people);
 }

 public static void printPeople(List&lt;Person&gt; people){
 for(Person p : people){
 System.out.println(p);
 }
 }
 }
</code></pre>

blocks|key|1299171|text|我遇到了一个类似的问题。必须对第三方类(对象)的列表进行排序。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1299172|List<ThirdPartyClass>+tpc+=+getTpcList(...);|code-block|syntax|javascript|1299173|ThirdPartyClass没有实现Java+Comparable接口。我从mkyong找到了一个很好的例子来说明如何解决这个问题。我不得不使用比较器方法进行排序。|offset|length|1299174|//Sort+ThirdPartyClass+based+on+the+value+of+some+attribute/function
Collections.sort(tpc,+Compare3rdPartyObjects.tpcComp);|1299175|其中，比较器是：|1299176|public+abstract+class+Compare3rdPartyObjects+{

public+static+Comparator<ThirdPartyClass>+tpcComp+=+new+Comparator<ThirdPartyClass>()+{

++++public+int+compare(ThirdPartyClass+tpc1,+ThirdPartyClass+tpc2)+{

++++++++Integer+tpc1Offset+=+compareUsing(tpc1);
++++++++Integer+tpc2Offset+=+compareUsing(tpc2);

++++++++//ascending+order
++++++++return+tpc1Offset.compareTo(tpc2Offset);

++++}
};

//Fetch+the+attribute+value+that+you+would+like+to+use+to+compare+the+ThirdPartyClass+instances+
public+static+Integer+compareUsing(ThirdPartyClass+tpc)+{

++++Integer+value+=+tpc.getValueUsingSomeFunction();
++++return+value;
}
}|1299177|entityMap|0|LINK|mutability|MUTABLE|url|https://www.mkyong.com/java/java-object-sorting-example-comparable-and-comparator/^0|0|0|13|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@$I|11|J|12|1|13]]|A|$]]|$1|K|3|L|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

I came across a similar problem. Had to sort a list of 3rd party class (objects).

<pre><code>List&lt;ThirdPartyClass&gt; tpc = getTpcList(...);
</code></pre>

ThirdPartyClass does not implement the Java Comparable interface. I found an excellent illustration from <a href="https://www.mkyong.com/java/java-object-sorting-example-comparable-and-comparator/" rel="nofollow noreferrer">mkyong</a> on how to approach this problem. I had to use the Comparator approach to sorting.

<pre><code>//Sort ThirdPartyClass based on the value of some attribute/function
Collections.sort(tpc, Compare3rdPartyObjects.tpcComp);
</code></pre>

where the Comparator is:

<pre><code>public abstract class Compare3rdPartyObjects {

public static Comparator&lt;ThirdPartyClass&gt; tpcComp = new Comparator&lt;ThirdPartyClass&gt;() {

 public int compare(ThirdPartyClass tpc1, ThirdPartyClass tpc2) {

 Integer tpc1Offset = compareUsing(tpc1);
 Integer tpc2Offset = compareUsing(tpc2);

 //ascending order
 return tpc1Offset.compareTo(tpc2Offset);

 }
};

//Fetch the attribute value that you would like to use to compare the ThirdPartyClass instances 
public static Integer compareUsing(ThirdPartyClass tpc) {

 Integer value = tpc.getValueUsingSomeFunction();
 return value;
}
}
</code></pre>

I have a generic <code>Collection</code> and am trying to work out how I can sort the items contained within it. I've tried a few things but I can't get any of them working.

How to sort a Collection<T>?

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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我有一个通用的Collection，正在尝试解决如何对其中包含的项进行排序。我试过几种方法，但都不能正常工作。

问如何对Collection<T>进行排序？
EN

回答 7

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