Question

I have the following content in a file that I need to parse.

((-2, -1 ), ( 4, 2) ) ((-1.2, 0), (0, 0)) 
((0, 0), (10, -1)) 
((5, 3), (5, 4)) ((5, 1) , (5, 5)) 
((8, 3), (10, 3)) 
((8, 5), (11.5, 5)) 

So far, I have scanned through the file and taken the input line by line, saving them as strings, so one string would be ((-2, -1 ), ( 4, 2) ) ((-1.2, 0), (0, 0)). My question is where to go from here. How do I extract the doubles from this String. I have tried to use the parentheses as a delimiter, as well as changing all of the parentheses to commas, and then using a comma as a delimiter, but both of these ways give me errors. Any ideas?

Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed group near index 1 at java.util.regex.Pattern.error(Unknown Source) at
    java.util.regex.Pattern.accept(Unknown Source) at
    java.util.regex.Pattern.group0(Unknown Source) at
    java.util.regex.Pattern.sequence(Unknown Source) at
    java.util.regex.Pattern.expr(Unknown Source) at
    java.util.regex.Pattern.compile(Unknown Source) at
    java.util.regex.Pattern.<init>(Unknown Source) at
    java.util.regex.Pattern.compile(Unknown Source) at
    java.lang.String.replaceAll(Unknown Source)

The whole purpose of this is to create points from these doubles. For example, ((0, 0), (10, -1)) would create two points, (0,0) and (10, -1). I have created the point class and it takes in two doubles in the constructor.
Here is what I tried:

      String toParse = "((0, 0), (10, -1))";
    toParse.replaceAll("(", ",");
    toParse.replaceAll(")", ",");
    Scanner stringScanner = new Scanner(toParse);
    stringScanner.useDelimiter(",");
    while(stringScanner.hasNextDouble()){

ect

Answer 1

The error message you get is because ( and ) are special regex characters: so whenever you want to replace (or match) them, you need to escape them with a backslash:

toParse.replaceAll("\\(", ",");
...

That said, you might want to use a Pattern/Matcher approach here:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Test {
    public static void main(String[] args) {

        String source =
                "((-2, -1 ), ( 4, 2) ) ((-1.2, 0), (0, 0))  \n" +
                "((0, 0), (10, -1))                         \n" +
                "((5, 3), (5, 4)) ((5, 1) , (5, 5))         \n" +
                "((8, 3), (10, 3))                          \n" +
                "((8, 5), (11.5, 5))                        \n";

        Matcher m = Pattern.compile("-?\\d+(\\.\\d+)?").matcher(source);

        while(m.find()) {
            double value = Double.parseDouble(m.group());
            System.out.println("value=" + value);
        }
    }
}

which produces:

value=-2.0
value=-1.0
value=4.0
value=2.0
value=-1.2
value=0.0
value=0.0
value=0.0
value=0.0
value=0.0
value=10.0
value=-1.0
value=5.0
value=3.0
value=5.0
value=4.0
value=5.0
value=1.0
value=5.0
value=5.0
value=8.0
value=3.0
value=10.0
value=3.0
value=8.0
value=5.0
value=11.5
value=5.0

What the code does: it searches for the pattern -?\d+(\.\d+)? and parses each string that matches said pattern to a double. The pattern itself means:

-?         # an optional minus sign
\d+        # followed by one or more digits
(\.\d+)?   # followed by an optional decimal DOT with one or more digits