Question

I am having some trouble with modifying Strings to be space delimited under the special case of adding spaces to all non-numerical characters.

My code must take a string representing a math equation, and split it up into it’s individual parts. It does so using space delimits between values This part works great if the string is already delimited.
The problem is that I do not always get a space delimited input. To deal with this, I want to first insert these spaces so that the array is created properly.

What my code must do is take any character that is NOT a number, and add a space before and after it.

Something like this:
3*24+321 becomes 3 * 24 + 321
or
((3.0)*(2.5)) becomes ( ( 3.0 ) * ( 2.5 ) )

Obviously I need to avoid inserting space in the numbers, or 2.5 becomes 2 . 5, and then gets entered into the array as 3 elements. which it is not.

So far, I have tried using

String InputLineDelmit = InputLine.replaceAll(“\B”, ” “);

which successfully changes a string of all letters “abcd” to “a b c d”
But it makes mistakes when it runs into numbers. Using this method, I have gotten that:

(((1)*(2))) becomes ( ( (1) * (2) ) ) —- * The numbers must be separate from parens

12.7+3.1 becomes 1 2.7+3.1 —– * 12.7 is split

51/3 becomes 5 1/3 —– * same issue

and 5*4-2 does not change at all.

So, I know that \D can be used as a regular expression for all non-numbers in java. However, my attempts to implement this (by replacing, or combining it with \B above) have led either to compiler errors or it REPLACING the char with a space, not adding one.

EDIT:

==== Answered! ====

It wont let me add my own answer because I’m new, but an edit to neo108’s code below (which, itself, does not work) did the job. What i did was change it to check isDigit, not isLetter, and then do nothing in that case (or in the special case of a decimal, for doubles). Else, the character is changed to have spaces on either side.

public static void main(String[] args){


    String formula = "12+((13.0)*(2.5)-17*2)+(100/3)-7";

    StringBuilder builder = new StringBuilder();

    for (int i = 0; i < formula.length(); i++){

        char c = formula.charAt(i);
        char cdot = '.';

        if(Character.isDigit(c) || c == cdot) {
        builder.append(c);
        }
        else {
        builder.append(" "+c+" ");
        }
    }   

    System.out.println("OUTPUT:" + builder);


}

OUTPUT: 12 + ( ( 13.0 ) * ( 2.5 ) – 17 * 2 ) + ( 100 / 3 ) – 7

However, any ideas on how to do this more succinctly, and also a decent explanation of StringBuilders, would be appreciated. Namely what is with this limit of 16 chars that I read about on javadocs, as the example above shows that you CAN have more output.

Answer 1

Something like this should work…

String formula = "Ab((3.0)*(2.5))";
StringBuilder builder = new StringBuilder();
for (int i = 0; i < formula.length(); i++){
    char c = formula.charAt(i);
    if(Character.isLetter(c)) {
        builder.append(" "+c+" ");
    } else {
        builder.append(c);
    }
}