public class Test {
final static int[] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
99999999, 999999999, Integer.MAX_VALUE };
static int sizeOfInt(int x) {
for (int i = 0;; i++)
if (x <= sizeTable[i])
return i + 1;
}
public static void main(String[] args) {
System.out.println(sizeOfInt(1234));
System.out.println(sizeOfInt(123));
System.out.println(sizeOfInt(12345));
System.out.println(sizeOfInt(12));
}
}

JAVA源码-实现INT位数统计