如何在特定范围内生成随机int值?

以下方法存在与整数溢出相关的错误:

randomNum = minimum + (int)(Math.random() * maximum);
// Bug: `randomNum` can be bigger than `maximum`.
Random rn = new Random();
int n = maximum - minimum + 1;
int i = rn.nextInt() % n;
randomNum =  minimum + i;
// Bug: `randomNum` can be smaller than `minimum`.

当前回答

我发现这个例子生成随机数:


此示例生成特定范围内的随机整数。

import java.util.Random;

/** Generate random integers in a certain range. */
public final class RandomRange {

  public static final void main(String... aArgs){
    log("Generating random integers in the range 1..10.");

    int START = 1;
    int END = 10;
    Random random = new Random();
    for (int idx = 1; idx <= 10; ++idx){
      showRandomInteger(START, END, random);
    }

    log("Done.");
  }

  private static void showRandomInteger(int aStart, int aEnd, Random aRandom){
    if ( aStart > aEnd ) {
      throw new IllegalArgumentException("Start cannot exceed End.");
    }
    //get the range, casting to long to avoid overflow problems
    long range = (long)aEnd - (long)aStart + 1;
    // compute a fraction of the range, 0 <= frac < range
    long fraction = (long)(range * aRandom.nextDouble());
    int randomNumber =  (int)(fraction + aStart);    
    log("Generated : " + randomNumber);
  }

  private static void log(String aMessage){
    System.out.println(aMessage);
  }
} 

此类的示例运行:

Generating random integers in the range 1..10.
Generated : 9
Generated : 3
Generated : 3
Generated : 9
Generated : 4
Generated : 1
Generated : 3
Generated : 9
Generated : 10
Generated : 10
Done.

其他回答

import java.util.Random;

public class RandomSSNTest {

    public static void main(String args[]) {
        generateDummySSNNumber();
    }


    //831-33-6049
    public static void generateDummySSNNumber() {
        Random random = new Random();

        int id1 = random.nextInt(1000);//3
        int id2 = random.nextInt(100);//2
        int id3 = random.nextInt(10000);//4

        System.out.print((id1+"-"+id2+"-"+id3));
    }

}

您也可以使用

import java.util.concurrent.ThreadLocalRandom;
Random random = ThreadLocalRandom.current();

然而,这个类在多线程环境中表现不佳。

你可以这样做:

import java.awt.*;
import java.io.*;
import java.util.*;
import java.math.*;

public class Test {

    public static void main(String[] args) {
        int first, second;

        Scanner myScanner = new Scanner(System.in);

        System.out.println("Enter first integer: ");
        int numOne;
        numOne = myScanner.nextInt();
        System.out.println("You have keyed in " + numOne);

        System.out.println("Enter second integer: ");
        int numTwo;
        numTwo = myScanner.nextInt();
        System.out.println("You have keyed in " + numTwo);

        Random generator = new Random();
        int num = (int)(Math.random()*numTwo);
        System.out.println("Random number: " + ((num>numOne)?num:numOne+num));
    }
}

您可以编辑第二个代码示例以:

Random rn = new Random();
int range = maximum - minimum + 1;
int randomNum =  rn.nextInt(range) + minimum;

只需执行以下语句即可完成:

Randomizer.generate(0, 10); // Minimum of zero and maximum of ten

下面是它的源代码。

文件Randomizer.java

public class Randomizer {
    public static int generate(int min, int max) {
        return min + (int)(Math.random() * ((max - min) + 1));
    }
}

它只是干净和简单。

public static void main(String[] args) {

    Random ran = new Random();

    int min, max;
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter min range:");
    min = sc.nextInt();
    System.out.println("Enter max range:");
    max = sc.nextInt();
    int num = ran.nextInt(min);
    int num1 = ran.nextInt(max);
    System.out.println("Random Number between given range is " + num1);

}