Question

This is the code I made:

public static boolean isOperator(char op){
    if (op == '+' || op == '-'
            || op == '*' || op == '/'
            || op == '^'
            || op == '(' || op == ')'){
        return true;
    }
    return false;
}

public static boolean isOperand(char op){
    String numbers = "0123456789.";
    int a = numbers.indexOf(op);
    return a >= 0;
}
public static void main(String []args){        
    String exp= "15+20+(3.84*25)*(78/3.8)";
    LinkedList a = new LinkedList();

    for (int i = 0; i < exp.length(); i++){
        if (isOperator(exp.charAt(i))){
            a.add(exp.charAt(i));
        } else if (isOperand(exp.charAt(i))){
            int k = i;
            while (k < exp.length()){//I see the length of the number
                if (isOperand(exp.charAt(k))){
                    k++;
                } else {
                    break;
                }
            }
            if (k != exp.length()-1){//if it's not ad the end
                a.add(exp.substring(i, k));
            } else {//if it's at the end I take all the remaining chars of the string
                a.add(exp.substring(i));
            }
            i = k-1;//i must go back since the subtring second parameter is exclusive
        } 
    }
    System.out.println(a);    
}//main

This is the output:

[15, +, 20, +, (, 3.84, *, 25, ), *, (, 78, /, 3.8), )]

Which is exactly what I wanted. As you can see I put operand and operators separately into a list maintaining the order of the string.
There is a way to do it in a simpler way?

Answer 1

Is there a way to do it in a simpler way?

Yes, there is. Use regular expressions. Take a look at the following code and
try to run it for your inputs.

public static void main(String[] args) 
{
    String exp = "15+20+(3.84*25)*(78/3.8)";
    String regex = "(\\d+\\.\\d+)|(\\d+)|([+-/*///^])|([/(/)])";

    Matcher m = Pattern.compile(regex).matcher(exp);

    LinkedList list = new LinkedList();

    while (m.find()) {
        list.add(m.group());
    }

    System.out.println(list);
}

Explanation of my regex used above:

“(\d+\.\d+)|(\d+)|([+-/*///^])|([/(/)])”

(double) or (integer) or (arithmetic operator) or (left/right paranthesis)