关于验证码随机数补齐高位

开始String类为我们提供了类似的功能，就是String.format

public class demo01 {
    public static void main(String[] args) {
        Random random = new Random();
        Integer i = random.nextInt(1000000);
        String newLabel = String.format("%s%06d", "", i);
        System.out.println(newLabel);
    }
}
------------------------------------

042309

Process finished with exit code 0

public static void main(String[] args) {
        long f = System.currentTimeMillis();
        for (int j = 0; j < 100000; j++) {
            Random random = new Random();
            Integer i = random.nextInt(1000000);
            String newLabel = String.format("%s%06d", "", i);
        }
        long e = System.currentTimeMillis();
        System.out.println(e-f);
    }
-------------------------
700+

后来字符串截取的方式实现

 

public class demo01 {
    public static void main(String[] args) {
        Random random = new Random();
        Double aDouble = random.nextDouble();
        String num = Double.toString(aDouble);
        String substring = num.substring(2, 8);
        System.out.println(num);
        System.out.println(substring);
    }
}
------------------------------------------------
0.07198521431173577
071985

public class demo01 {
    public static void main(String[] args) {
        long f = System.currentTimeMillis();
        for (int i = 0; i < 100000; i++) {
            Random random = new Random();
            Double aDouble = random.nextDouble();
            String num = Double.toString(aDouble);
            String substring = num.substring(2, 8);
        }
        long e = System.currentTimeMillis();
        System.out.println(e-f);
    }
}
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62到125之间