Make a method to divide a string in java

Question

I have a class called: ComplexNumber and I have a string that I need to convert into a ComplexNumber (Using Java).

If I have: "5+3i" or "6-2i", how do I appropriately parse these strings. I need to get it to 2 variables and I can do the rest.

String complexNum = "5+3i"; 

I would need to split the previous string into two double type variables double real = 5;
double imag = 3;

String complexNum = "6-2i";

I would need to split the previous string into two double type variables double real = 6; double imag = -2;

Can anyone give example code as to how they would go about doing this? There aren't any spaces to use as delimeters and I don't completely understand regular expressions (i've read a bunch of tutorials but it still doesn't click)

---

EDIT:

If regex is the best bet, i just have a hard time understanding how to create an appropriate expression.

I have the following code prepared:

String num = "5+2i";
String[] splitNum = num.split();

And i'm trying to figure out how to write the appropriate regex.

Answer 1

Alternative 1

How about somewhat like this?

String complexNum = "5+3i"; 
String regex = "(\\d+)[+-](\\d+)i";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(complexNum);

if(matcher.find()){
   int real = Integer.parseInt(matcher.group(1));
   int imag = Integer.parseInt(matcher.group(2));
}

If you need to make the sign part of the number, then change the regular expression to

String regex = "(\\d+)([+-]\\d+)i"

This will make the sign part of the second matching group.

Alternative 2

Alternatively, if you are positively sure that the string is properly formatted and you do not care about the sing of the imaginary part, you could do something like this:

Scanner sc = new Scanner(complexNum).useDelimiter("[i+-]");
int real = sc.nextInt();
int imag = sc.nextInt();

Which is simpler.

Alternative 3

And if you're not sure of the format of the string, you can still use the regex to validate it:

if(complexNum.matches("(\\d+)[+-](\\d+)i")) {
  //scanner code here
} else {
   //throw exception or handle the case
}

Alternative 4

String[] tokens = complexNum.split("[i+-]");
int real = Integer.parseInt(tokens[0]);
int imag = Integer.parseInt(tokens[1]);
System.out.println(real +  " " + imag);

Answer 2

Parsing complex number isn't that easy, because the real and img part could also contain a sign and an exponent. You could use apache-commons-math.

ComplexFormat cf = new ComplexFormat();
Complex c = cf.parse("1.110 + 2.222i");

Answer 3

Try this :

    String complexNum = "5+3i"; 
    int j = 0 ;
    String real = getNumber();
    j++;
    String imag = getNumber();   

public String getNumber()
{
      String num ;
      char c;
      int temp;
      for( ; j < complexNum.length() ; j++)
       {
           c = complexNum.charAt(j);
           temp = (int) c;
           if(temp > 57 ||temp < 48)
                 break;
           else
                  num += c;
       }
     return num;
}

Answer 4

Your regex should look something like this: (\\d+)([-+])(\\d+)i where \\d+ will match any number of digits, [+-] will match either a + or a -, and the i simply matches itself. The () are used to select out parts of the string that match.

Some code adapted from this link:

    // Compile the patten.
Pattern p = Pattern.compile("(\\d+)([-+])(\\d+)i");

// Match it.
Matcher m = p.matcher(string);

// Get all matches.
while (m.find() == true)
    System.out.println("Real part " + m.group(1) +
                 " sign " m.group(2) +
         " and imagionary part " + m.group(3));

Those will, of course, still be strings, so you will need to use something like

int real = Integer.parseInt(m.group(1))

to get the values into integer form, and you could use an if statement to fix the sign on the imaginary part, e.g.

if(m.group(2).equals("-"))
    imaginary *= -1;
    //if the value is positive, we don't have to multiply it by anything

UPDATE: Edwin Dalorzo's comment above simplifies this code. Use the regex "(\\d+)([+-]\\d+)i" to capture the sign of the imaginary part, and then no if statement is necessary.