Subtracting strings

Question

I was asked to create a JOptionPane program which takes as many numbers as the user wants (as a string) and sums them together. I thought about a pseudo like this:

1. make int Total = 0
2. receive input as string X
3. loop: for (int i = 0; i<=X.length();i++)
   1. create another string S1 which takes the number from the beginning until the first space
   2. convert S1 into a number and add it to Total
   3. subtract S1 from X, and start the loop over
4. show total

So, my problem is at subtracting the S1 from the X.

My code so far:

public static void main(String[] args) {
int total = 0;
    String x = JOptionPane.showInputDialog("enter nums please");
    for (int i = 0; i<=x.length();i++){
        String s1 = x.substring (0, x.indexOf(' '));
        total += Integer.parseInt(s1);  
        x = x - s1;
    }
    JOptionPane.showMessageDialog(null, "the sum is" + total); }

Answer 1

This is another interpretation of the method @ZouZou used, but doesn't actually break up your string, it remembers where its already looked, and works its way along the string

int total = 0;
String inputString = "12 7 8 9 52";
int prevIndex = 0;
int index = 0;
while (index > -1) {
  index = inputString.indexOf(' ', prevIndex);
  if (index > -1) {
    total += Integer.parseInt(inputString.substring(prevIndex, index));
    prevIndex = index + 1;
  } else {
    total += Integer.parseInt(inputString.substring(inputString.lastIndexOf(' ')+1));
break;
  }
}
System.out.println(total);

Answer 2

If you didn't learn arrays yet, you can implement this like that :

public static void main(String[] args){
        int total = 0;
        String x = "12 7";
        String s1 = x.trim(); //trim the string
        while(!s1.isEmpty()){ //loop until s1 is not empty
            int index = x.indexOf(' ');//search the index for a whitespace
            if(index != -1){ //we found a whitespace in the String !
                s1 = s1.substring(0, index); //substract the right number
                total += Integer.parseInt(s1); 
                x = x.substring(index+1).trim(); //update the String x by erasing the number we just added to total
                s1 = x; //update s1
            } else {
                total += Integer.parseInt(s1); //when there is only one integer left in the String
                break; //break the loop this is over
            }
        }
        System.out.println(total);
    }

Answer 3

Simple solution

int total = 0;
String x = JOptionPane.showInputDialog("enter nums please");

for (String s : x.split("\\s+")){
    total += Integer.parseInt(s);
}

System.out.println(total);

Edit: "can't use arrays"- then use a Scanner to scan the String for nextInt()

int total = 0;
String x = JOptionPane.showInputDialog("enter nums please");
Scanner scanner = new Scanner(x);  // use scanner to scan the line for nextInt()

while (scanner.hasNext()){
    total += scanner.nextInt();
}
System.out.println(total);