blocks|key|1127212|text|只需生成ID并检查它是否已经存在于您生成的ID列表中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1127213|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Just generate ID and check whether it is already present or not in your list of generated IDs.

blocks|key|1342397|text|int+uniqueId+=+0;

int+getUniqueId()
{
++++return+uniqueId%2B%2B;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1342398|如果你想让它是线程安全的，就添加synchronized。|unstyled|offset|length|style|CODE|1342399|entityMap^0|0|G|C|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>int uniqueId = 0;

int getUniqueId()
{
 return uniqueId++;
}
</code></pre>

Add <code>synchronized</code> if you want it to be thread safe.

blocks|key|1342412|text|UUID+class|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1342413|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/j2se/1.5.0/docs/api/java/util/UUID.html^0|0|A|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/UUID.html" rel="nofollow noreferrer">UUID class</a>

blocks|key|1342471|text|它需要有多独特？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342472|如果它只在一个进程中是唯一的，那么您可以使用一个AtomicInteger并在每次需要一个新值时调用incrementAndGet()。|offset|length|style|CODE|1342473|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/javase/6/docs/api/java/util/concurrent/atomic/AtomicInteger.html|1|http://java.sun.com/javase/6/docs/api/java/util/concurrent/atomic/AtomicInteger.html#incrementAndGet%2528%2529^0|0|O|D|1E|H|O|D|0|1E|H|1|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@$D|T|E|U|F|G]|$D|V|E|W|F|G]]|9|@$D|X|E|Y|1|Z]|$D|10|E|11|1|12]]|A|$]]|$1|H|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]|P|$5|K|L|M|A|$N|Q]]]]

How unique does it need to be?

If it's only unique within a process, then you can use an <a href="http://java.sun.com/javase/6/docs/api/java/util/concurrent/atomic/AtomicInteger.html" rel="noreferrer"><code>AtomicInteger</code></a> and call <a href="http://java.sun.com/javase/6/docs/api/java/util/concurrent/atomic/AtomicInteger.html#incrementAndGet%28%29" rel="noreferrer"><code>incrementAndGet()</code></a> each time you need a new value.

blocks|key|1342518|text|如果你有一些限制，这很容易。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342519|如果您只有一个线程，则只需使用uniqueID%2B%2B；请确保在退出时存储当前的uniqueID。|1342520|如果您有多个线程，则使用一个通用的同步generateUniqueID方法(实现方式与上面相同)。|1342521|问题是当您有许多CPU时--或者在集群中，或者在像点对点游戏这样的分布式设置中。|1342522|在这种情况下，通常可以将两个部分组合成一个数字。例如，每个生成唯一ID的进程都可以分配自己的2字节ID号，然后将其与uniqueID%2B%2B组合。类似于：|1342523|return+(myID+<<+16)+&+uniqueID%2B%2B|code-block|syntax|javascript|1342524|分发"myID“部分可能很棘手，但有一些方法。你可以从一个集中的数据库中获取一个，从一个集中的服务器请求一个唯一的ID，...|1342525|如果您使用的是Long而不是Int，其中一个常见的技巧是获取ETH0的设备id+(UUID)，这对于服务器来说是唯一的--然后只需添加一个序列号即可。|1342526|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|Z|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

It's easy if you are somewhat constrained.

If you have one thread, you just use uniqueID++; Be sure to store the current uniqueID when you exit.

If you have multiple threads, a common synchronized generateUniqueID method works (Implemented the same as above).

The problem is when you have many CPUs--either in a cluster or some distributed setup like a peer-to-peer game.

In that case, you can generally combine two parts to form a single number. For instance, each process that generates a unique ID can have it's own 2-byte ID number assigned and then combine it with a uniqueID++. Something like:

<pre><code>return (myID &lt;&lt; 16) &amp; uniqueID++
</code></pre>

It can be tricky distributing the "myID" portion, but there are some ways. You can just grab one out of a centralized database, request a unique ID from a centralized server, ...

If you had a Long instead of an Int, one of the common tricks is to take the device id (UUID) of ETH0, that's guaranteed to be unique to a server--then just add on a serial number.

blocks|key|1342558|text|如果你真正想要的是整型而不是整型：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342559|Integer+id+=+new+Integer(42);+//+will+not+==+any+other+Integer|code-block|syntax|javascript|1342560|如果您希望JVM之外的内容对其他进程或用户可见、持久化或许多其他考虑因素，那么还有其他方法，但如果没有上下文，最好使用系统中内置的对象标识唯一性。|1342561|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you really meant integer rather than int:

<pre><code>Integer id = new Integer(42); // will not == any other Integer
</code></pre>

If you want something visible outside a JVM to other processes or to the user, persistent, or a host of other considerations, then there are other approaches, but without context you are probably better off using using the built-in uniqueness of object identity within your system.

blocks|key|1342585|text|+import+java.util.UUID;

+public+class+IdGenerator+{
++++public+static+int+generateUniqueId()+{++++++
++++++++UUID+idOne+=+UUID.randomUUID();
++++++++String+str=""%2BidOne;++++++++
++++++++int+uid=str.hashCode();
++++++++String+filterStr=""%2Buid;
++++++++str=filterStr.replaceAll("-",+"");
++++++++return+Integer.parseInt(str);
++++}

++++//+XXX:+replace+with+java.util.UUID

++++public+static+void+main(String[]+args)+{
++++++++for+(int+i+=+0;+i+<+5;+i%2B%2B)+{
++++++++++++System.out.println(generateUniqueId());
++++++++++++//generateUniqueId();
++++++++}
++++}

}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1342586|希望这对你有帮助。|unstyled|1342587|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code> import java.util.UUID;

 public class IdGenerator {
 public static int generateUniqueId() { 
 UUID idOne = UUID.randomUUID();
 String str=""+idOne; 
 int uid=str.hashCode();
 String filterStr=""+uid;
 str=filterStr.replaceAll("-", "");
 return Integer.parseInt(str);
 }

 // XXX: replace with java.util.UUID

 public static void main(String[] args) {
 for (int i = 0; i &lt; 5; i++) {
 System.out.println(generateUniqueId());
 //generateUniqueId();
 }
 }

}
</code></pre>

Hope this helps you.

blocks|key|1127434|text|在任何时候都是唯一的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1127435|int+uniqueId+=+(int)+(System.currentTimeMillis()+&+0xfffffff);|code-block|syntax|javascript|1127436|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|$]]

Unique at any time:

<pre><code>int uniqueId = (int) (System.currentTimeMillis() &amp; 0xfffffff);
</code></pre>

blocks|key|1127463|text|如果只需要int，那么AtomicInteger可以让它成为可能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1127464|如果需要字符串，那么下面的代码应该通过混合使用timeStamp和AtomicLong来工作。|1127465|AtomicLong+idCounter+=++new+AtomicLong(100);
long+timestamp+=+System.currentTimeMillis();
long+nextLong+=+idCounter.incrementAndGet();
String+randomId+=+String.valueOf(timestamp)%2BString.valueOf(nextLong);+|code-block|syntax|javascript|1127466|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 only int is required then AtomicInteger can make it possible.
if String is needed then the below code should work by mixing timeStamp and
AtomicLong.
<pre><code>AtomicLong idCounter = new AtomicLong(100);
long timestamp = System.currentTimeMillis();
long nextLong = idCounter.incrementAndGet();
String randomId = String.valueOf(timestamp)+String.valueOf(nextLong); 
</code></pre>

How to generate unique ID that is integer in java that not guess next number?

问如何在Java (Integer)中生成唯一ID？
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