随机返回真或假

Question

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

Answer 1

The class java.util.Random already has this functionality:

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

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

public class YourClass {

    /* Oher stuff here */

    private Random random;

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

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

    /* More stuff here */

}

Answer 2

(Math.random() < 0.5)随机返回真或假

Answer 3

This should do:

public boolean randomBoolean(){
    return Math.random() < 0.5;
}

Answer 4

You can use the following 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 < 10; i++) {
            System.out.println(randomBoolean.getBoolean());
        }
    }
}

Answer 5

你会得到它：

return Math.random() < 0.5;

Answer 6

You can use the following for an unbiased result:

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

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!

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) < 2) ? true : false;

Answer 7

Java's Random 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 cmd command to get their value. So in this example I will use the Available Physical Memory as a source of randomness.

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());
        }
    }
}

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

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:

1. There is some delay in executing this program. Please notice that in the main() function , inside the while(true) loop, there is no Thread.sleep() and still, output is printed to console only about once a second or so.
2. 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.

Answer 8

ThreadLocalRandom.current().nextBoolean()

To avoid recreating Random objects, use ThreadLocalRandom . Every thread has just one such object.

boolean rando = ThreadLocalRandom.current().nextBoolean() ;

That code is so short and easy to remember that you need not bother to create a dedicated method as asked in the Question.