blocks|key|2913408|text|类java.util.Random已经具有以下功能：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2913409|public+boolean+getRandomBoolean()+{
++++Random+random+=+new+Random();
++++return+random.nextBoolean();
}|code-block|syntax|javascript|2913410|但是，每次需要一个随机布尔值时，总是创建一个新的Random实例并不是很有效。相反，在您的类中创建一个需要随机布尔值的Random类型的属性，然后将该实例用于每个新的随机布尔值：|2913411|public+class+YourClass+{

++++/*+Oher+stuff+here+*/

++++private+Random+random;

++++public+YourClass()+{
++++++++//+...
++++++++random+=+new+Random();
++++}

++++public+boolean+getRandomBoolean()+{
++++++++return+random.nextBoolean();
++++}

++++/*+More+stuff+here+*/

}|2913412|entityMap^0|1|G|0|0|O|6|1N|6|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

The class <code>java.util.Random</code> already has this functionality:

<pre><code>public boolean getRandomBoolean() {
 Random random = new Random();
 return random.nextBoolean();
}
</code></pre>

However, it's not efficient to always create a new <code>Random</code> instance each time you need a random boolean. Instead, create a attribute of type <code>Random</code> in your class that needs the random boolean, then use that instance for each new random booleans:

<pre><code>public class YourClass {

 /* Oher stuff here */

 private Random random;

 public YourClass() {
 // ...
 random = new Random();
 }

 public boolean getRandomBoolean() {
 return random.nextBoolean();
 }

 /* More stuff here */

}
</code></pre>

blocks|key|2913391|text|(Math.random()+<+0.5)随机返回true或false|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2913392|entityMap^0|0|L|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

<code>(Math.random() &lt; 0.5)</code> returns true or false randomly

blocks|key|2913417|text|这应该可以做到：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2913418|public+boolean+randomBoolean(){
++++return+Math.random()+<+0.5;
}|code-block|syntax|javascript|2913419|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|$]]

This should do:

<pre><code>public boolean randomBoolean(){
 return Math.random() &lt; 0.5;
}
</code></pre>

blocks|key|2913421|text|您可以使用以下代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2913422|public+class+RandomBoolean+{
++++Random+random+=+new+Random();
++++public+boolean+getBoolean()+{
++++++++return+random.nextBoolean();
++++}
++++public+static+void+main(String[]+args)+{
++++++++RandomBoolean+randomBoolean+=+new+RandomBoolean();
++++++++for+(int+i+=+0;+i+<+10;+i%2B%2B)+{
++++++++++++System.out.println(randomBoolean.getBoolean());
++++++++}
++++}
}|code-block|syntax|javascript|2913423|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|$]]

You can use the following code
<pre><code>public class RandomBoolean {
 Random random = new Random();
 public boolean getBoolean() {
 return random.nextBoolean();
 }
 public static void main(String[] args) {
 RandomBoolean randomBoolean = new RandomBoolean();
 for (int i = 0; i &lt; 10; i++) {
 System.out.println(randomBoolean.getBoolean());
 }
 }
}
</code></pre>

blocks|key|242165|text|您将通过以下方式获得它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|242166|return+Math.random()+<+0.5;|code-block|syntax|javascript|242167|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|$]]

You will get it by this:

<pre><code>return Math.random() &lt; 0.5;
</code></pre>

blocks|key|2913493|text|您可以使用以下内容以获得无偏差的结果：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2913494|Random+random+=+new+Random();
//For+50%25+chance+of+true
boolean+chance50oftrue+=+(random.nextInt(2)+==+0)+?+true+:+false;|code-block|syntax|javascript|2913495|注：+random.nextInt(2)表示数字2是界。计数从0开始。所以我们有两个可能的数字(0和1)，因此概率是50%25！|offset|length|style|BOLD|2913496|如果你想给你的结果更多的概率为真(或假)，你可以调整上面的如下！|2913497|Random+random+=+new+Random();

//For+50%25+chance+of+true
boolean+chance50oftrue+=+(random.nextInt(2)+==+0)+?+true+:+false;

//For+25%25+chance+of+true
boolean+chance25oftrue+=+(random.nextInt(4)+==+0)+?+true+:+false;

//For+40%25+chance+of+true
boolean+chance40oftrue+=+(random.nextInt(5)+<+2)+?+true+:+false;|2913498|entityMap^0|0|0|0|2|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You can use the following for an unbiased result:

<pre><code>Random random = new Random();
//For 50% chance of true
boolean chance50oftrue = (random.nextInt(2) == 0) ? true : false;
</code></pre>

Note: random.nextInt(2) means that the number 2 is the bound. the counting starts at 0. So we have 2 possible numbers (0 and 1) and hence the probability is 50%!

If you want to give more probability to your result to be true (or false) you can adjust the above as following! 

<pre><code>Random random = new Random();

//For 50% chance of true
boolean chance50oftrue = (random.nextInt(2) == 0) ? true : false;

//For 25% chance of true
boolean chance25oftrue = (random.nextInt(4) == 0) ? true : false;

//For 40% chance of true
boolean chance40oftrue = (random.nextInt(5) &lt; 2) ? true : false;
</code></pre>

blocks|key|242214|text|Java的Random类使用CPU的内部时钟(据我所知)。类似地，可以使用RAM信息作为随机性的来源。只需打开Windows任务管理器的性能选项卡，并查看物理内存-可用:它不断变化；大多数时间，该值大约每秒更新一次，只有在极少数情况下，该值保持不变几秒钟。更改更频繁的其他值是系统句柄和线程，但我没有找到cmd命令来获取它们的值。因此，在本例中，我将使用可用物理内存作为随机性来源。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|242215|import+java.io.BufferedReader;
import+java.io.IOException;
import+java.io.InputStreamReader;

public+class+Main+{

++++public+String+getAvailablePhysicalMemoryAsString()+throws+IOException
++++{
++++++++Process+p+=+Runtime.getRuntime().exec("cmd+/C+systeminfo+%7C+find+\"Available+Physical+Memory\"");
++++++++BufferedReader+in+=+
++++++++++++++++new+BufferedReader(new+InputStreamReader(p.getInputStream()));
++++++++return+in.readLine();
++++}

++++public+int+getAvailablePhysicalMemoryValue()+throws+IOException
++++{
++++++++String+text+=+getAvailablePhysicalMemoryAsString();
++++++++int+begin+=+text.indexOf(":")%2B1;
++++++++int+end+=+text.lastIndexOf("MB");
++++++++String+value+=+text.substring(begin,+end).trim();

++++++++int+intValue+=+Integer.parseInt(value);
++++++++System.out.println("available+physical+memory+in+MB+=+"%2BintValue);
++++++++return+intValue;
++++}

++++public+boolean+getRandomBoolean()+throws+IOException
++++{
++++++++int+randomInt+=+getAvailablePhysicalMemoryValue();
++++++++return+(randomInt%252==1);
++++}


++++public+static+void+main(String+args[])+throws+IOException
++++{+++++++
++++++++Main+m+=+new+Main();
++++++++while(true)
++++++++{
++++++++++++System.out.println(m.getRandomBoolean());
++++++++}
++++}
}|code-block|syntax|javascript|242216|如您所见，核心部分正在使用Runtime.getRuntime().exec()运行cmd+systeminfo命令。|242217|为简洁起见，我省略了try-catch语句。我多次运行这个程序，没有出现任何错误--在cmd命令的输出中总是有一个“可用物理内存”行。|242218|可能的缺点：|242219|242220|在执行此程序时会有一些延迟。请注意，在while(true)循环内的main()函数中，没有Thread.sleep()，而且输出大约每秒打印到控制台一次。|ordered-list-item|242221|对于新打开的操作系统会话，可用内存可能是恒定的-请验证。我只有几个程序在运行，而且值几乎每秒都在变化。我猜如果您在服务器环境中运行此程序，那么为每个调用获取不同的值应该不是问题。|242222|242223|entityMap^0|5|6|48|3|4X|6|0|0|D|R|1A|A|0|0|0|0|J|B|Y|6|1A|E|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|17|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|18|8|@$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|E|@]|F|$]]|$1|N|3|O|5|6|7|1D|8|@]|E|@]|F|$]]|$1|P|3|Q|5|6|7|1E|8|@]|E|@]|F|$]]|$1|R|3|-4|5|6|7|1F|8|@]|E|@]|F|$]]|$1|S|3|T|5|U|7|1G|8|@$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]]|E|@]|F|$]]|$1|V|3|W|5|U|7|1N|8|@]|E|@]|F|$]]|$1|X|3|-4|5|6|7|1O|8|@]|E|@]|F|$]]|$1|Y|3|-4|5|6|7|1P|8|@]|E|@]|F|$]]]|Z|$]]

Java's <code>Random</code> class makes use of the CPU's internal clock (as far as I know). Similarly, one can use RAM information as a source of randomness. Just open Windows Task Manager, the Performance tab, and take a look at Physical Memory - Available: it changes continuously; most of the time, the value updates about every second, only in rare cases the value remains constant for a few seconds. Other values that change even more often are System Handles and Threads, but I did not find the <code>cmd</code> command to get their value. So in this example I will use the Available Physical Memory as a source of randomness.

<pre><code>import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

 public String getAvailablePhysicalMemoryAsString() throws IOException
 {
 Process p = Runtime.getRuntime().exec("cmd /C systeminfo | find \"Available Physical Memory\"");
 BufferedReader in = 
 new BufferedReader(new InputStreamReader(p.getInputStream()));
 return in.readLine();
 }

 public int getAvailablePhysicalMemoryValue() throws IOException
 {
 String text = getAvailablePhysicalMemoryAsString();
 int begin = text.indexOf(":")+1;
 int end = text.lastIndexOf("MB");
 String value = text.substring(begin, end).trim();

 int intValue = Integer.parseInt(value);
 System.out.println("available physical memory in MB = "+intValue);
 return intValue;
 }

 public boolean getRandomBoolean() throws IOException
 {
 int randomInt = getAvailablePhysicalMemoryValue();
 return (randomInt%2==1);
 }


 public static void main(String args[]) throws IOException
 { 
 Main m = new Main();
 while(true)
 {
 System.out.println(m.getRandomBoolean());
 }
 }
}
</code></pre>

As you can see, the core part is running the cmd <code>systeminfo</code> command, with <code>Runtime.getRuntime().exec()</code>. 

For the sake of brevity, I have omitted try-catch statements. I ran this program several times and no error occured - there is always an 'Available Physical Memory' line in the output of the cmd command. 

Possible drawbacks:

<ol>
<li>There is some delay in executing this program. Please notice that in the <code>main()</code> function , inside the <code>while(true)</code> loop, there is no <code>Thread.sleep()</code> and still, output is printed to console only about once a second or so.</li>
<li>The available memory might be constant for a newly opened OS session - please verify. I have only a few programs running, and the value is changing about every second. I guess if you run this program in a Server environment, getting a different value for every call should not be a problem.</li>
</ol>

I need to create a Java method to return <code>true</code> or <code>false</code> randomly. How can I do this?

Return True or False Randomly

服务器

Windows

Java

我需要创建一个Java方法来随机返回true或false。我该怎么做呢？

问随机返回True或False
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回答 7

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