コードと検証結果
※標準クラスのみ用いる．
検証コード
import java.util.*;
public class Main {
public static void main(String[] args) throws Exception {
int l = 20;
int n = 1005;
System.out.println("-------------------------[Use String.format()]-------------------------");
long start = System.nanoTime();
System.out.println(String.format("%0" + l + "d", n));
System.out.println(((double)(System.nanoTime() - start) / 1__000__000__000));
System.out.println("-------------------------[Get length of 'n' with log10, and zero padding with for loop]-------------------------");
start = System.nanoTime();
int nLen = (int)Math.log10((double)n) + 1;
String preStr = (nLen >= l) ? "" : repeatStr("0", l - nLen);
System.out.println(preStr + n);
System.out.println(((double)(System.nanoTime() - start) / 1__000__000__000));
System.out.println("-------------------------[Get length of 'n' by getting length of String 'n', and zero padding with for loop]-------------------------");
start = System.nanoTime();
int nLen2 = Integer.toString(n).length();
String preStr2 = (nLen2 >= l) ? "" : repeatStr("0", l - nLen2);
System.out.println(preStr2 + n);
System.out.println(((double)(System.nanoTime() - start) / 1__000__000__000));
System.out.println("-------------------------[Get length of 'n' by looping dividing with 10, and zero padding with for loop]-------------------------");
start = System.nanoTime();
int nLen3 = getNumLenByDividing10(n);
String preStr3 = (nLen3 >= l) ? "" : repeatStr("0", l - nLen3);
System.out.println(preStr3 + n);
System.out.println(((double)(System.nanoTime() - start) / 1__000__000__000));
}
public static String repeatStr(String str, int repeatNum) {
String res = "";
if(repeatNum <= 0) {
return res;
}
for(int i = 0; i < repeatNum; i++) {
res += str;
}
return res;
}
public static int getNumLenByDividing10(int n) {
int nLen = 0;
while(n != 0) {
n /= 10;
nLen++;
}
return nLen;
}
}
// l=4, n=100
-------------------------[Use String.format()]-------------------------
0100
0.021760815
-------------------------[Get length of 'n' with log10, and zero padding with for loop]-------------------------
0100
0.010855948
-------------------------[Get length of 'n' by getting length of String 'n', and zero padding with for loop]-------------------------
0100
4.34719E-4
-------------------------[Get length of 'n' by looping dividing with 10, and zero padding with for loop]-------------------------
0100
2.98369E-4
// l=20, n=100
-------------------------[Use String.format()]-------------------------
00000000000000000100
0.021191799
-------------------------[Get length of 'n' with log10, and zero padding with for loop]-------------------------
00000000000000000100
0.010872442
-------------------------[Get length of 'n' by getting length of String 'n', and zero padding with for loop]-------------------------
00000000000000000100
4.8769E-4
-------------------------[Get length of 'n' by looping dividing with 10, and zero padding with for loop]-------------------------
00000000000000000100
3.23475E-4
// l=20, n=1020553
-------------------------[Use String.format()]-------------------------
00000000000001020553
0.020495513
-------------------------[Get length of 'n' with log10, and zero padding with for loop]-------------------------
00000000000001020553
0.009346566
-------------------------[Get length of 'n' by getting length of String 'n', and zero padding with for loop]-------------------------
00000000000001020553
4.89392E-4
-------------------------[Get length of 'n' by looping dividing with 10, and zero padding with for loop]-------------------------
00000000000001020553
3.36254E-4
// l=4, n=1020553
-------------------------[Use String.format()]-------------------------
1020553
0.020645082
-------------------------[Get length of 'n' with log10, and zero padding with for loop]-------------------------
1020553
0.01026944
-------------------------[Get length of 'n' by getting length of String 'n', and zero padding with for loop]-------------------------
1020553
4.14849E-4
-------------------------[Get length of 'n' by looping dividing with 10, and zero padding with for loop]-------------------------
1020553
2.85072E-4
