Sword finger offer 20 String representing numeric value

. Can't appear before . perhaps e;
e You have to appear before ,e Then there must be an integer
± Appear in the 0 Location or e/E The first position behind is legal

class Solution {
    
    public boolean isNumber(String s) {
    
        if(s == null || s.length() == 0){
    
            return false;
        }
        // Mark whether the corresponding situation is encountered 
        boolean numSeen = false;
        boolean dotSeen = false;
        boolean eSeen = false;
        char[] str = s.trim().toCharArray();
        for(int i = 0;i < str.length; i++){
    
            if(str[i] >= '0' && str[i] <= '9'){
    
                numSeen = true;
            }else if(str[i] == '.'){
    
                //. Can't appear before . perhaps e
                if(dotSeen || eSeen){
    
                    return false;
                }
                dotSeen = true;
            }else if(str[i] == 'e' || str[i] == 'E'){
    
                //e Can't appear before e, Number of required occurrences 
                if(eSeen || !numSeen){
    
                    return false;
                }
                eSeen = true;
                numSeen = false;// Reset numSeen, exclude 123e perhaps 123e+ The situation of , Make sure e Then there are several 
            }else if(str[i] == '-' || str[i] == '+'){
    
                //+- Appear in the 0 Location or e/E The first position behind is legal 
                if(i != 0 && str[i-1] != 'e' && str[i-1] != 'E'){
    
                    return false;
                }
            }else{
    // Other illegal characters 
                return false;
            }
        }
        return numSeen;
    }
}