how can I check if a string is a floating point number?

Question

In my program I'm going to store user input in an array then going to check each character to see if it's a digit or dot or E or negative sign after that I'll store it in to an array called temps.

Now I have problem in my fleating method () that don't how should I make my condition for the pattern of floating number digit-digit-dot-digit-digit (e.g 12.22)

I have my work here:

public void sorting(String data) {
    String[] temps = new String[200];
    int cpos = 0;
    int tpos = 0;

    Arrays.fill(temps, null);

    if (str.isEmpty() == false) {
        char char1 = str.charAt(cpos);

        int i = 0;
        while (i < str.length()) {
            char1 = str.charAt(cpos);

            char1 = str.charAt(tpos);
            System.out.println("the current value is  " + char1 + " ");
            tpos++;

            if (Character.isDigit(char1)) {
                temps[cpos] = "Digit";
                // System.out.println(" this number is digit");
                cpos++;
            } else if (char1 == 'e' || char1 == 'E') {
                temps[cpos] = "s_notaion";
                cpos++;
            } else if (char1 == '-') {
                temps[cpos] = "negative";
                cpos++;
            } else if (char1 == '.') {
                temps[cpos] = ".";
                cpos++;
            }
            i++;
        }
    }
}

here is the method for floating number

private static boolean floating(String [] data) {
    int count =0;
    boolean correct = false;
    for (int i = 0; i < data.length; i++) {

         if (data[i]== "Digit" )
             && data[i]=="." && data[i]"Digit"){
             // here is the problem for the condition 
         }

    }
    return false; 
}

Answer 1

The easiest way to test if a String can represent a float is to try to parse it:

String testString = "1.2345";
double result;
try {
  result = Double.parseDouble(testString);
  System.out.println("Success!")
  }
catch (NumberFormatException nfe) {
  // wasn't a double, deal with the failure in whatever way you like
}

Answer 2

If I understood correctly, the Data array has stuff like ["Digit","Digit",".","Digit"]

So you want the

private static boolean floating(String [] data) { method to return true if the array only has "Digit" entries and exactly one "." entry? is that it?

If so:

boolean foundLeDigit = false;
for (int i = 0; i < data.length; i++) {

     if (data[i].equals("Digit") == false && data[i].equals(".") == false  {
        //we found something other than a Digit or . it's not a float
       return false;
     }
    if(data[i].equals(".")) { 
     if(foundLeDigit) { return false; //as we found 2 "." }
    foundLeDigit = true
    }


}
return foundLeDigit; 

Answer 3

The questions lacks a bit of context, so for my answer I'm going to presume that this is homework requiring a manual solution, and that all floating point numbers are supposed to be accepted.

Your approach (while over-engineered) is half-right: you are reducing the input string into classes of characters - digit, sign, exponent marker. What is missing is that now you have to make sure that these character classes come in the right order.

Identify the various parts of float numbers (just look at 0, -1.0, 400E30, 42.1E-30) and you'll see that they come in a specific order, even if some are optional, and that each part imposes restrictions on what characters are allowed there. For example, if there is an 'E' in the number, it has to be followed by a number (with optional sign).

So as you step through the characters of the string, think about how you could keep track of where you are in the number, and base your character validation on that (this is the state machine @JonKiparsky was mentioning).

A few small things:

• Don't compare strings with '==' - use equalsTo().
• Think about what it means if sorting() finds a character which is neither a digit, a sign, or the exponent 'E'?
• You allocate the temps array for 200 entries, but the input string could be larger.

Answer 4

using the regular expression is the best way to Handel this problem

private static boolean floating(String [] data) {
        int count =0;
        boolean correct = false;
        for (int i = 0; i < data.length; i++) {

            if (str.matches("((-|\\+)?[0-9]+(\\.[0-9]+)?)+")){
                System.out.println(" it's a floating number ");
                correct= true;
                break;
             }else 
                 correct = false;

        }if (correct ==true){
            return true;
        }else 
        return false; 

    }