如何在Java中生成100个随机的3位数字？

Question

I need to generate 100 random 3 digit numbers. I have figured out how to generate 1 3 digit number. How do I generate 100? Here's what I have so far...

import java.util.Random;

public class TheNumbers {
    public static void main(String[] args) {
      System.out.println("The following is a list of 100 random" + 
          " 3 digit numbers.");
      Random rand= new Random();

          int pick = rand.nextInt(900) + 100;
          System.out.println(pick);


}

}

Answer 1

The basic concept is to use a for-next loop, in which you can repeat your calculation the required number of times...

You should take a look at The for Statement for more details

Random rnd = new Random(System.currentTimeMillis());
for (int index = 0; index < 100; index++) {
    System.out.println(rnd.nextInt(900) + 100);
}

Now, this won't preclude generating duplicates. You could use a Set to ensure the uniqueness of the values...

Set<Integer> numbers = new HashSet<>(100);
while (numbers.size() < 100) {
    numbers.add(rnd.nextInt(900) + 100);
}
for (Integer num : numbers) {
    System.out.println(num);
}

Answer 2

Try for loop

for(int i=0;i<100;i++)
      {
          int pick = rand.nextInt(900) + 100;
          System.out.println(pick);
      }

Answer 3

If you adapt the following piece of code to your problem

    for(int i= 100 ; i < 1000 ; i++) {
        System.out.println("This line is printed 900 times.");
    }

, it will do what you want.

Answer 4

Using the answer to the question Generating random numbers in a range with Java :

import java.util.Random;

public class TheNumbers {
    public static void main(String[] args) {
      System.out.println("The following is a list of 100 random 3 digit nums.");
      Random rand = new Random();
      for(int i = 1; i <= 100; i++) {
        int randomNum = rand.nextInt((999 - 100) + 1) + 100;
        System.out.println(randomNum);
      }
}

Answer 5

This solution is an alternative if the 3-digit numbers include numbers that start with 0 (if for example you are generating PIN codes), such as 000, 011, 003 etc.

Set<String> codes = new HashSet<>(100);
Random rand = new Random();
while (codes.size() < 100)
{
   StringBuilder code = new StringBuilder();
   code.append(rand.nextInt(10));
   code.append(rand.nextInt(10));
   code.append(rand.nextInt(10));

   codes.add(code.toString());
}

for (String code : codes) 
{
    System.out.println(code);
}