5.随机数

一.Random

新建RandomDemo.java

public class RandomDemo {

	public static void main(String[] args) {

		StringBuilder sb = new StringBuilder(5);
		//生成五位随机数,但是UUID只能生成到f而且没有大写
		sb.append(UUID.randomUUID().toString().substring(2, 7));
		System.out.println(sb.toString());

		//创建一个包含大小写英文字母,和数字的StringBuilder
		StringBuilder strb = new StringBuilder("abcdefghijklmnopqrstuvwxyz");
		strb.append(strb.toString().toUpperCase());
		strb.append("0123456789");

		StringBuilder sb2 = new StringBuilder(5);
		for (int j = 0; j < 5; j++) {
			//通过生成随机索引,返回该索引的字符
			int i = new Random().nextInt(strb.length() - 1);
			sb2.append(strb.charAt(i));
		}
		System.out.println(sb2);
	}
}

二.ThreadLocalRandom

ThreadLocalRandom tlr = ThreadLocalRandom.current();
System.out.println(tlr.nextInt(10));//生成0-10之间的随机数
System.out.println(tlr.nextInt(5,10));//生成5-10之间的随机数

三.UUID

StringBuilder sb = new StringBuilder(5);
//生成五位随机数,但是UUID只能生成到f而且没有大写
sb.append(UUID.randomUUID().toString().substring(2, 7));
System.out.println(sb.toString());