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)

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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);