blocks|key|2987469|text|您应该查看它调用的HashSet构造函数的源代码...它是一个特殊的构造函数，它使后端的Map成为LinkedHashMap而不仅仅是HashMap。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2987470|entityMap^0|9|7|18|3|1D|D|1V|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

You should look at the source of the <code>HashSet</code> constructor it calls... it's a special constructor that makes the backing <code>Map</code> a <code>LinkedHashMap</code> instead of just a <code>HashMap</code>.

blocks|key|278743|text|答案就在中，LinkedHashSet使用哪个构造函数来构造基类：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|278744|public+LinkedHashSet(int+initialCapacity,+float+loadFactor)+{
++++super(initialCapacity,+loadFactor,+true);++++++//+<--+boolean+dummy+argument
}

...

public+LinkedHashSet(int+initialCapacity)+{
++++super(initialCapacity,+.75f,+true);++++++++++++//+<--+boolean+dummy+argument
}

...

public+LinkedHashSet()+{
++++super(16,+.75f,+true);+++++++++++++++++++++++++//+<--+boolean+dummy+argument
}

...

public+LinkedHashSet(Collection<?+extends+E>+c)+{
++++super(Math.max(2*c.size(),+11),+.75f,+true);+++//+<--+boolean+dummy+argument
++++addAll(c);
}|code-block|syntax|javascript|278745|下面描述了一个接受布尔参数的HashSet构造函数(一个示例)，它看起来如下所示：|278746|/**
+*+Constructs+a+new,+empty+linked+hash+set.++(This+package+private
+*+constructor+is+only+used+by+LinkedHashSet.)+The+backing
+*+HashMap+instance+is+a+LinkedHashMap+with+the+specified+initial
+*+capacity+and+the+specified+load+factor.
+*
+*+@param++++++initialCapacity+++the+initial+capacity+of+the+hash+map
+*+@param++++++loadFactor++++++++the+load+factor+of+the+hash+map
+*+@param++++++dummy+++++++++++++ignored+(distinguishes+this
+*+++++++++++++constructor+from+other+int,+float+constructor.)
+*+@throws+++++IllegalArgumentException+if+the+initial+capacity+is+less
+*+++++++++++++than+zero,+or+if+the+load+factor+is+nonpositive
+*/
HashSet(int+initialCapacity,+float+loadFactor,+boolean+dummy)+{
++++map+=+new+LinkedHashMap<E,Object>(initialCapacity,+loadFactor);
}|278747|entityMap^0|4|T|6|D|0|0|0|15|E|7|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|W|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|D]]|E|@]|F|$]]|$1|N|3|O|5|I|7|12|8|@]|E|@]|F|$J|K]]|$1|P|3|-4|5|6|7|13|8|@]|E|@]|F|$]]]|Q|$]]

The answer lies in which constructors the <code>LinkedHashSet</code> uses to construct the base class:

<pre><code>public LinkedHashSet(int initialCapacity, float loadFactor) {
 super(initialCapacity, loadFactor, true); // &lt;-- boolean dummy argument
}

...

public LinkedHashSet(int initialCapacity) {
 super(initialCapacity, .75f, true); // &lt;-- boolean dummy argument
}

...

public LinkedHashSet() {
 super(16, .75f, true); // &lt;-- boolean dummy argument
}

...

public LinkedHashSet(Collection&lt;? extends E&gt; c) {
 super(Math.max(2*c.size(), 11), .75f, true); // &lt;-- boolean dummy argument
 addAll(c);
}
</code></pre>

And (one example of) a <code>HashSet</code> constructor that takes a boolean argument is described, and looks like this:

<pre><code>/**
 * Constructs a new, empty linked hash set. (This package private
 * constructor is only used by LinkedHashSet.) The backing
 * HashMap instance is a LinkedHashMap with the specified initial
 * capacity and the specified load factor.
 *
 * @param initialCapacity the initial capacity of the hash map
 * @param loadFactor the load factor of the hash map
 * @param dummy ignored (distinguishes this
 * constructor from other int, float constructor.)
 * @throws IllegalArgumentException if the initial capacity is less
 * than zero, or if the load factor is nonpositive
 */
HashSet(int initialCapacity, float loadFactor, boolean dummy) {
 map = new LinkedHashMap&lt;E,Object&gt;(initialCapacity, loadFactor);
}
</code></pre>

blocks|key|276949|text|LinkedHashSet的构造函数调用以下基类构造函数：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|276950|HashSet(int+initialCapacity,+float+loadFactor,+boolean+dummy)+{
++map+=+new+LinkedHashMap<E,+Object>(initialCapacity,+loadFactor);
}|code-block|syntax|javascript|276951|如您所见，内部映射是一个LinkedHashMap。如果您查看LinkedHashMap内部，您将发现以下字段：|276952|private+transient+Entry<K,+V>+header;|276953|这就是有问题的链表。|276954|entityMap^0|0|D|0|0|C|D|V|D|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|R|$]]

<code>LinkedHashSet</code>'s constructors invoke the following base class constructor:

<pre><code>HashSet(int initialCapacity, float loadFactor, boolean dummy) {
 map = new LinkedHashMap&lt;E, Object&gt;(initialCapacity, loadFactor);
}
</code></pre>

As you can see, the internal map is a <code>LinkedHashMap</code>. If you look inside <code>LinkedHashMap</code>, you'll discover the following field:

<pre><code>private transient Entry&lt;K, V&gt; header;
</code></pre>

This is the linked list in question.

blocks|key|2987546|text|如果您查看一下从LinkedHashSet类调用的构造函数，就会发现在内部它是一个用于备份目的的LinkedHashMap。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2987547|entityMap^0|8|D|1C|D|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

If you take a look at the constructors called from the <code>LinkedHashSet</code> class you will see that internally it's a <code>LinkedHashMap</code> that is used for backing purpose.

blocks|key|282648|text|HashSet:实际上是无序的。如果你传递这个参数意味着|type|unstyled|depth|inlineStyleRanges|entityRanges|data|282649|Set<Integer>+set=new+HashSet<Integer>();
for(int+i=0;i<set.length;i%2B%2B)
{
++SOP(set)`enter+code+here`
}|code-block|syntax|javascript|282650|输出:可能是2,1,3不可预测。下一次是另一个订单。|offset|length|style|CODE|282651|产生先进先出指令的LinkedHashSet()。|282652|entityMap^0|0|0|6|5|0|9|F|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@$I|W|J|X|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

HashSet:
Unordered actually.
if u passing the parameter means

<pre><code>Set&lt;Integer&gt; set=new HashSet&lt;Integer&gt;();
for(int i=0;i&lt;set.length;i++)
{
 SOP(set)`enter code here`
}
</code></pre>

Out Put:
May be <code>2,1,3</code> not predictable. next time another order.

<code>LinkedHashSet()</code> which produce FIFO Order.

blocks|key|280614|text|HashSet是无序和无序的集合。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|280615|LinkedHashSet是HashSet的订购版本。|280616|HashSet和LinkedHashSet之间的唯一区别是：|280617|LinkedHashSet会维护插入顺序。|280618|当我们遍历HashSet时，顺序是不可预测的，而对于LinkedHashSet.，顺序是可预测的|280619|LinkedHashSet保持插入顺序的原因是：|280620|底层使用的数据结构是Doubly-Linked-List.|280621|entityMap^0|0|7|0|0|D|0|0|7|8|D|0|0|D|0|5|7|Q|D|0|0|D|0|A|I|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|17|8|@$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|N|3|O|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|R|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|S|$]]

HashSet is unordered and unsorted Set. 
LinkedHashSet is the ordered version of HashSet. 

The only difference between HashSet and LinkedHashSet is that: 
LinkedHashSet maintains the insertion order. 

When we iterate through a HashSet, the order is unpredictable while it is predictable in case of LinkedHashSet. 

The reason for how LinkedHashSet maintains insertion order is that: 
The underlying used data structure is Doubly-Linked-List.

blocks|key|278808|text|所有的方法和构造函数都是相同的，但唯一的区别是LinkedHashset将保持插入顺序，但它不允许重复。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|278809|Hashset将不会维护任何插入顺序。它是List和Set的组合，简单:)|278810|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|$]]

All Methods and constructors are same but only one difference is LinkedHashset will maintain insertion order but it will not allow duplicates.

Hashset will not maintain any insertion order.
It is combination of List and Set simple :)

blocks|key|282683|text|我建议你大部分时间使用LinkedHashSet，因为它有更好的整体性能()：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|282684|对于插入操作，|282685|Predictable+iteration+order+LinkedHashSet+(Oracle)|ordered-list-item|282686|LinkedHashSet的开销比HashSet更高；|282687|的性能通常比HashMap，略好，因为我们大部分时间都使用集合结构进行迭代。|282688|282689|282690|+性能测试：|blockquote|282691|282692|282693|-------------+TreeSet+-------------
+size+++++++add++contains+++iterate
+++10+++++++746+++++++173++++++++89
++100+++++++501+++++++264++++++++68
+1000+++++++714+++++++410++++++++69
10000++++++1975+++++++552++++++++69
-------------+HashSet+-------------
+size+++++++add++contains+++iterate
+++10+++++++308++++++++91++++++++94
++100+++++++178++++++++75++++++++73
+1000+++++++216+++++++110++++++++72
10000+++++++711+++++++215+++++++100
----------+LinkedHashSet+----------
+size+++++++add++contains+++iterate
+++10+++++++350++++++++65++++++++83
++100+++++++270++++++++74++++++++55
+1000+++++++303+++++++111++++++++54
10000++++++1615+++++++256++++++++58|code-block|syntax|javascript|282694|你可以在这里看到源码测试页面：The+Final+Performance+Testing+Example|282695|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashSet.html|1|http://www.artima.com/weblogs/viewpost.jsp?thread=122295^0|B|D|W|5|B|D|0|0|0|B|C|9|S|M|0|0|0|6|7|6|7|0|0|0|1|5|0|0|0|0|F|11|1|0^^$0|@$1|2|3|4|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|1K|8|@]|E|@]|F|$]]|$1|I|3|J|5|K|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]]|E|@$9|1Q|A|1R|1|1S]]|F|$]]|$1|L|3|M|5|K|7|1T|8|@]|E|@]|F|$]]|$1|N|3|O|5|K|7|1U|8|@$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|D]]|E|@]|F|$]]|$1|P|3|-4|5|6|7|1Z|8|@]|E|@]|F|$]]|$1|Q|3|-4|5|6|7|20|8|@]|E|@]|F|$]]|$1|R|3|S|5|T|7|21|8|@$9|22|A|23|B|C]]|E|@]|F|$]]|$1|U|3|-4|5|6|7|24|8|@]|E|@]|F|$]]|$1|V|3|-4|5|6|7|25|8|@]|E|@]|F|$]]|$1|W|3|X|5|Y|7|26|8|@]|E|@]|F|$Z|10]]|$1|11|3|12|5|6|7|27|8|@]|E|@$9|28|A|29|1|2A]]|F|$]]|$1|13|3|-4|5|6|7|2B|8|@]|E|@]|F|$]]]|14|$15|$5|16|17|18|F|$19|1A]]|1B|$5|16|17|18|F|$19|1C]]]]

I suggest you to use <code>LinkedHashSet</code> most of the time, because it has better performance overall):

<ol>
<li>Predictable iteration order <a href="https://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashSet.html" rel="noreferrer">LinkedHashSet (Oracle)</a></li>
<li>LinkedHashSet is more expensive for insertions than HashSet;</li>
<li>In general slightly better performance than <code>HashMap</code>, because the most of the time we use Set structures for iterating.</li>
</ol>

<blockquote>
 Performance tests:
</blockquote>

<pre><code>------------- TreeSet -------------
 size add contains iterate
 10 746 173 89
 100 501 264 68
 1000 714 410 69
10000 1975 552 69
------------- HashSet -------------
 size add contains iterate
 10 308 91 94
 100 178 75 73
 1000 216 110 72
10000 711 215 100
---------- LinkedHashSet ----------
 size add contains iterate
 10 350 65 83
 100 270 74 55
 1000 303 111 54
10000 1615 256 58
</code></pre>

You can see source test page here: <a href="http://www.artima.com/weblogs/viewpost.jsp?thread=122295" rel="noreferrer">The Final Performance Testing Example</a>

blocks|key|2987719|text|HashSet:|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2987720|带下划线的数据结构是Hashtable。重复的对象不是allowed.insertion，顺序不会被保留，它是基于对象的哈希码。空插入是可能的(只有一次)。它实现了可序列化的、可克隆的，但不是RandomAccess接口。如果频繁操作是搜索操作，则最好选择HashSet。|2987721|HashSet副本中的|2987722|不是allowed.if用户试图插入副本，而我们不会得到任何编译或运行时异常。add方法返回简单的false。|blockquote|2987723|2987724|2987725|构造函数：|2987726|2987727|+HashSet+h=new+HashSet()；创建一个空的HashSet对象，默认初始容量为16，默认填充比(加载因子)为0.75。|2987728|2987729|HashSet+h=new+HashSet(int+initialCapacity)；创建一个具有指定initialCapacity的空HashSet对象，默认填充比率为0.75。|2987730|HashSet+h=new+HashSet(int+initialCapacity，float+fillRatio)；|2987731|HashSet+h=new+HashSet+(集合c)；为给定集合创建等效的HashSet对象。此构造函数用于集合对象之间的内部转换。|2987732|2987733|LinkedHashSet:|2987734|它是HashSet的子类。它与HashSet包括(构造函数和方法)完全相同，除了以下区别。|2987735|Differences：|2987736|带下划线的数据结构不是Hashtable.|2987737|Insertion+order+is+preserved.|unordered-list-item|2987738|
|2987739|introduced+1.2+。|2987740|2987741|LinkedHashSet：|2987742|在1.4版本中，带下划线的数据结构是preserved.|2987743|Indroduced和|2987744|的组合。|ordered-list-item|2987745|2987746|2987747|entityMap^0|0|8|0|0|0|0|0|0|0|5|0|0|0|0|0|0|0|0|0|E|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1U|8|@$9|1V|A|1W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1X|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1Z|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|20|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|21|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|22|8|@$9|23|A|24|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|25|8|@]|D|@]|E|$]]|$1|R|3|S|5|L|7|26|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|27|8|@]|D|@]|E|$]]|$1|U|3|V|5|6|7|28|8|@]|D|@]|E|$]]|$1|W|3|X|5|6|7|29|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|6|7|2A|8|@]|D|@]|E|$]]|$1|10|3|-4|5|6|7|2B|8|@]|D|@]|E|$]]|$1|11|3|12|5|6|7|2C|8|@$9|2D|A|2E|B|C]]|D|@]|E|$]]|$1|13|3|14|5|6|7|2F|8|@]|D|@]|E|$]]|$1|15|3|16|5|6|7|2G|8|@]|D|@]|E|$]]|$1|17|3|18|5|6|7|2H|8|@]|D|@]|E|$]]|$1|19|3|1A|5|1B|7|2I|8|@]|D|@]|E|$]]|$1|1C|3|1D|5|6|7|2J|8|@]|D|@]|E|$]]|$1|1E|3|1F|5|1B|7|2K|8|@]|D|@]|E|$]]|$1|1G|3|-4|5|6|7|2L|8|@]|D|@]|E|$]]|$1|1H|3|1I|5|6|7|2M|8|@]|D|@]|E|$]]|$1|1J|3|1K|5|6|7|2N|8|@]|D|@]|E|$]]|$1|1L|3|1M|5|1B|7|2O|8|@]|D|@]|E|$]]|$1|1N|3|1O|5|1P|7|2P|8|@]|D|@]|E|$]]|$1|1Q|3|-4|5|6|7|2Q|8|@]|D|@]|E|$]]|$1|1R|3|-4|5|6|7|2R|8|@]|D|@]|E|$]]|$1|1S|3|-4|5|6|7|2S|8|@]|D|@]|E|$]]]|1T|$]]

HashSet:

The underlined data structure is Hashtable.
Duplicate objects are not allowed.insertion order is not preserved and it is based on hash code of objects.
Null insertion is possible(only once).
It implements Serializable, Clonable but not RandomAccess interface.
HashSet is best choose if frequent operation is search operation.

<blockquote>
 In HashSet duplicates are not allowed.if users are trying to insert duplicates when we won't get any compile or runtime exceptions. add method returns simply false.
</blockquote>

Constructors:

<blockquote>
 HashSet h=new HashSet(); creates an empty HashSet object with default initial capacity 16 and default fill ratio(Load factor) is 0.75 .
 
 HashSet h=new HashSet(int initialCapacity); creates an empty HashSet object with specified initialCapacity and default fill ration is 0.75.
 
 HashSet h=new HashSet(int initialCapacity, float fillRatio);
 
 HashSet h=new HashSet(Collection c); creates an equivalent HashSet object for the given collection. This constructor meant for inter conversion between collection object.
</blockquote>

LinkedHashSet:

It is a child class of HashSet. it is exactly same as HashSet including(Constructors and Methods) except the following differences.

Differences
HashSet:

<ol>
<li>The underlined data structure is Hashtable.</li>
<li>Insertion order is not preserved.</li>
<li>introduced 1.2 version.</li>
</ol>

LinkedHashSet:

<ol>
<li>The underlined data structure is a combination of LinkedList and Hashtable.</li>
<li>Insertion order is preserved.</li>
<li>Indroduced in 1.4 version.</li>
</ol>

blocks|key|278896|text|HashSet+不维护插入项的顺序|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|278897|LinkedHashSet+maintain+insertion+item的顺序|278898|示例|278899|Set<String>+set+=+...;//+using+new+HashSet<>()+OR+new+LinkedHashSet<>()
set.add("2");
set.add("1");
set.add("ab");
for(String+value+:+set){
+++System.out.println(value);
}++|code-block|syntax|javascript|278900|HashSet输出|278901|1
ab
2|278902|LinkedHashSet输出|278903|2
1
ab|278904|entityMap^0|0|7|8|3|0|0|D|E|8|0|0|0|0|7|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|D]]|E|@]|F|$]]|$1|I|3|J|5|6|7|19|8|@]|E|@]|F|$]]|$1|K|3|L|5|M|7|1A|8|@]|E|@]|F|$N|O]]|$1|P|3|Q|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|E|@]|F|$]]|$1|R|3|S|5|M|7|1E|8|@]|E|@]|F|$N|O]]|$1|T|3|U|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|E|@]|F|$]]|$1|V|3|W|5|M|7|1I|8|@]|E|@]|F|$N|O]]|$1|X|3|-4|5|6|7|1J|8|@]|E|@]|F|$]]]|Y|$]]

<code>HashSet</code> don't maintain the order of insertion item 
<code>LinkedHashSet</code> maintain the order of insertion item

Example

<pre><code>Set&lt;String&gt; set = ...;// using new HashSet&lt;&gt;() OR new LinkedHashSet&lt;&gt;()
set.add("2");
set.add("1");
set.add("ab");
for(String value : set){
 System.out.println(value);
} 
</code></pre>

<code>HashSet</code> output

<pre><code>1
ab
2
</code></pre>

<code>LinkedHashSet</code> output

<pre><code>2
1
ab
</code></pre>

What is the difference between them? I know that 

<blockquote>
 A LinkedHashSet is an ordered version of HashSet that
 maintains a doubly-linked List across all elements. Use this class instead of HashSet
 when you care about the iteration order. When you iterate through a HashSet the
 order is unpredictable, while a LinkedHashSet lets you iterate through the elements
 in the order in which they were inserted. 
</blockquote>

But in sourcecode of LinkedHashSet there are only calling constructors of HashSet. So where is double-linked List and insertion order?

HashSet vs LinkedHashSet

数据结构

性能测试

它们之间的区别是什么？我知道 A LinkedHashSet是HashSet的有序版本，它跨所有元素维护一个双向链表。当您关心迭代顺序时，请使用此类而不是HashSet。当您遍历HashSet时，顺序是不可预测的，而LinkedHashSet允许您按照元素插入的顺序遍历元素。但在LinkedHashSet源码中，只有H...

问HashSet vs LinkedHashSet
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