写一个函数其1到n为自然数，用于计算这里面1的个数的和。
f(0)=0;
f(1)=1;
f(2)=1;
.
.
f(10)=2;
f(11)=4;
f(12)=5;
以此类推……

import java.util.Date;

public class Test {
/* public int oneCount(int number) {
int count = 0;
for (int i = 0; i <=number; i++) {
String n = String.valueOf(i);
for (int j = 0; j < n.length(); j++) {
if (n.charAt(j) == 1) {
count++;
}
}

}
return count;
}
*/
public static void main(String[] args) {
Date dt = new Date();
int count = 0;
System.out.println("Start Time at :" + dt.getTime());

for (int i = 0; i <= 1111111111; i++) {
String n = String.valueOf(i);
for (int j = 0; j < n.length(); j++) {
if (n.charAt(j) == '1') {
count++;
}
}

}
System.out.println(count);
Date dt2 = new Date();
System.out.println("End Time at :" + dt2.getTime());

}