Output of the code

public class Model {
private Scanner sc = new Scanner(System.in);

private String expression;
private String exp[];


    public Model()
    {
        expression = sc.nextLine();
        split();
    }
    
    public void split()
    {
        
        //splitting the entered expression to array of operators alone and array of the numbers then create Arraylist to combine the operators and numbers together as if it is a string expression  but as an array
        String num[]= this.expression.split("[/ /*/-]");
        String preop[]= this.expression.split("[0123456789]"); // this will give [empty, operator, operator...] therefore we will create another array to fill in the ops excluding empty
       
        
                    System.out.println("Test: Printing num Array");
                    for(int i = 0; i<num.length;i  )
                        {
                    System.out.print(num[i] ",");
                        }
                    System.out.println("\nTest: Printing preOp Array");
                    for(int i = 0; i<preop.length;i  )
                    {
                    System.out.print(preop[i]  ",");
                    }
                
        
        
        ArrayList<String> op = new ArrayList<>();//I used arraylist because easier
        for(int i = 1; i<preop.length;i  )
        {
            op.add(preop[i]);
        }
        
                System.out.println("\nTest of the fixed preOp array: "   op);
                
                
        //putting the operands and the operators together in the same array
                
        ArrayList<String> exp = new ArrayList<>();
        //fill the arraylist with numbers then add the operators to it by using number (index of the operator  1  count)
        for(int i = 0; i <num.length;i  )
        {
            exp.add(num[i]);
        }
        int count = 0;
        for(int i = 0; i <op.size();i  )
        {
            exp.add(i 1 count, op.get(i));
            count  ;
        }
        
                System.out.println("Test: "   exp);
    }

The problem is that the op array is giving empty slot [op, op, empty, op] whenever user inputs a double digit numbers in the expression.

I was expecting similar results when user enters one digit numbers where it gives the intended results as in the image input with one digit numbers

CodePudding user response：

it is because this

this.expression.split("[0123456789]");

You split by a single digit, so 43 is split into 2 parts as well with an empty string in between. Also, you don't need to name all the digits in the regex, you can just do a range "[0-9]". If you want to match for 1 or more digits add a . This should work:

this.expression.split("[0-9] ");

CodePudding user response：

You can solve it in one go using a regex to split at any of the operators and keeping them using lookahead and lookbehind:

public static void main(String[] args) {
    String first  = "3 2*3-4";
    String second = "3 2-43*3";

    System.out.println(Arrays.toString(splitExpression(first)));
    System.out.println(Arrays.toString(splitExpression(second)));
}

static String[] splitExpression(String input){
    String regex = "((?<=(\\ |\\-|\\*|\\/))|(?=(\\ |\\-|\\*|\\/)))";
    return input.split(regex);
}

output:

[3,  , 2, *, 3, -, 4]
[3,  , 2, -, 43, *, 3]