Leetcode#65||Valid Number

public class Solution {
public boolean isNumber(String s) {
int length = s.length();

int i = 0;
int e = length - 1;

while (i < length && Character.isWhitespace(s.charAt(i))) {
i++;
}

if (i == length) {
return false;
}

while (e >= i && Character.isWhitespace(s.charAt(e))) {
e--;
}

if (s.charAt(i) == '+' || s.charAt(i) == '-') {
i++;
}

boolean isNum = false;
boolean hasDot = false;
boolean hasExp = false;

while (i <= e) {
char c = s.charAt(i);

if (Character.isDigit(c)) {
isNum = true;
} else if (c == '.') {
if (hasDot || hasExp) {
return false;
}
hasDot = true;
} else if (c == 'e') {
if (hasExp || !isNum) {
return false;
}
hasExp = true;
isNum = false;
} else if (c == '+' || c == '-') {
if (s.charAt(i - 1) != 'e') {
return false;
}
} else {
return false;
}
i++;
}

return isNum;
}
}