java实用小功能案例

// 生成20-30之间的随机数
Random rand = new Random();
int num = rand.nextInt(11)+21;
// Math 类中的 random 方法返回一个 [0.0, 1.0) 区间的 double 值。下面这段代码能得到一个 min 和 max 之间的随机数：
int randomWithMathRandom = (int) ((Math.random() * (max - min)) + min);
// [3-1)
int randomWithMathRandom = (int) ((Math.random() * (3 - 1)) + 1);

String ZiMu = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGJKLZXCVBNM1234567890";
    String result = "";
    Random random = new Random();
    for (int i = 0; i < 4; i++) {
        int index = random.nextInt(ZiMu.length());
        char c = ZiMu.charAt(index);
        result += c;
    }
    System.out.print(result);

Date dNow = new Date( );
SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd hh:mm:ss");
System.out.println("当前时间为: " + ft.format(dNow));

public class test {
    public static void main(String[] args) {
        ZonedDateTime zonedDateTime = ZonedDateTime.now();
        System.out.println(zonedDateTime);
    }
}