[問題]獲取一個整數有多少位

swift 代碼

func getDigits(with number: Int) -> Int {
    var digit = 1
    var num = number
    while num / 10 != 0 {
        num /= 10
        digit += 1
    }
    return digit
}
var stringTime: TimeInterval = 0
var digitTime: TimeInterval = 0
for _ in 0 ..< 10000000 {
    let num = Int(arc4random())
    do {
        let start = Date().timeIntervalSince1970
        let _ = String(num).count
        let end = Date().timeIntervalSince1970
        stringTime += (end - start)
    }
    do {
        let start = Date().timeIntervalSince1970
        let _ = getDigits(with: num)
        let end = Date().timeIntervalSince1970
        digitTime += (end - start)
    }
    
}
print("轉換成字符串: \(stringTime)")
print("經過計算: \(digitTime)")

複製代碼

Java 代碼

import java.util.Date;
import java.util.Random;

class Digit {
    public static void main(final String[] args) {
        Random r = new Random();

        long stringTime = 0;
        long digitTime = 0;

        for (int i = 0; i < 10000000; i++) {
            int number = r.nextInt(10);
            {
                long start = (new Date()).getTime();
                int count = ("" + number).length();
                long end = (new Date()).getTime();
                stringTime += (end - start);
            }
            {
                long start = (new Date()).getTime();
                int count = Digit.getDigits(number);
                long end = (new Date()).getTime();
                digitTime += (end - start);
            }
        }
        System.out.print("轉換成字符串:"+ stringTime+"\n");
        System.out.print("經過計算:"+ digitTime+"\n");
    }

    static int getDigits(final int number) {
        int digit = 1;
        int num = number;

        while (num / 10 != 0) {
            num /= 10;
            digit += 1;
        }
        return digit;
    }
}
複製代碼

---

Swift 10次樣本 單位：s

序號	轉換成字符串	經過計算
1	1.6021199226379395	2.122344493865967
2	1.6038966178894043	2.126537322998047
3	1.6078293323516846	2.1316823959350586
4	1.5953664779663086	2.11974835395813
5	1.6008284091949463	2.1262362003326416
6	1.5975737571716309	2.117039918899536
7	1.573176383972168	2.0912203788757324
8	1.553645372390747	2.068214178085327
9	1.5619103908538818	2.075680732727051
10	1.5425021648406982	2.0574917793273926

Java 10次樣本 單位：ms

序號	轉換成字符串	經過計算
1	686	453
2	533	427
3	508	447
4	516	395
5	528	419
6	515	416
7	511	376
8	523	362
9	526	397
10	524	384

疑問：一樣是很大的數字 Swift 的表現是轉成字符串獲取位數比直接計算的方式耗時少， 而在 java 中表現相反 而且 java 總體用時好像比 swift 要少 why？？？