Valid Number,判断是否为合法数字

问题描述：

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

?

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public boolean isNumber(String s)     {         s = s.trim();         if (s.length() == 0) return false;         boolean hasE = false;         boolean hasDot = false;         boolean hasNumber = false;                   for (int i = 0; i < s.length(); i++)         {             // e cannot be the first character             if (i == 0 && s.charAt(i) == 'e') return false;             if (s.charAt(i) == 'e') {                 // e cannot be replicated nor placed before number                 if (hasE == true || hasNumber == false) {                     return false;                 } else {                     hasE = true;                 }             }                           if (s.charAt(i) == '.') {                 // '.' cannot be replicated nor placed after 'e'                 if (hasDot == true || hasE == true) {                     return false;                 } else {                     hasDot = true;                 }             }             // the sign can be placed at the beginning or after 'e'             if (i != 0 && s.charAt(i - 1) != 'e' && (s.charAt(i) == '+' || s.charAt(i) == '-')) return false;                           // no other chacraters except '+', '-', '.', and 'e'             if ((s.charAt(i) > '9' || s.charAt(i) < '0') && s.charAt(i) != '+' && s.charAt(i) != '-' && s.charAt(i) != '.' && s.charAt(i) != 'e')             return false;                            // check whether numbers are included.             if (s.charAt(i) <= '9' && s.charAt(i) >= '0')             {                 hasNumber = true;             }         }         // '+', '-', and 'e' cannot be the last character         if (s.charAt(s.length() - 1) == '-' || s.charAt(s.length() - 1) == '+' || s.charAt(s.length() - 1) == 'e') return false;           return hasNumber;     } }