How to split numbers from a string in Java?

You may use regular expressions for this. Here is the solution for the simple case (just integers). The \\d is an decimal and the plus + says once or more. For more information look at http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html .

import java.util.regex.*;

public class Main {
  public static void main(String[] args) {
    Pattern p = Pattern.compile("\\d+");
    Matcher m = p.matcher("(345+3)*/3");
    while(m.find())
      System.out.println(m.group());
  }
}

You can use regular expressions. Here is a (very rough) sketch:

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

String findIntegerOccurrence(String inputString)
{
    // Define pattern to match your numbers here.
    Pattern pattern = Pattern.compile("... reg expr here...");
    Matcher matcher = pattern.matcher(inputString);

    if (matcher.find()) // Checks if the regular expression matches.
    {
        // Extract the substring of inputString that has matched
        return matcher.group();
    }
    else
    {
        return null;
    }
}

You basically need to define an appropriate regular expression for your numbers and then use it to find all occurrences inside the input string. The above example is only a sketch to see how you define a regular expression and match it. Since you want to match all occurrences of numbers and separate them from the rest of the input, you will need a more elaborate solution (the above example only shows which classes you need and some useful methods).

You can find all the details on regular expressions in Java in the Java documentation

EDIT

Removed edit: I had added a description of the needed regular expression but the same regular expression has been added as a comment to another answer a few minutes before I could complete my changes. Please refer to the other answer.

If you do not need the non-numeric characters, do the following:

Parse the string once, replacing all non-numeric characters with a space. The, parse the resulting string, removing double spaces as you go along. the input string gi356f would first become _356, with _ being spaces. If you then remove the double spaces, you'd have what you were looking for.

Another example d45*9j becomes _45_9_ and then, when you split it into substrings, you will have 45 and 9 and seperate numbers.

There are many ways to do this, the best way is to try different approaches until you find something that works for you.

I'm creating a Calculator too and I'm using Stacks to split the equation into Numbers and Operators, just like @Gaurav said. Here's the code that I'm using:

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

            equationChar = String.valueOf(equation.charAt(i));

            if (numbers.contains(equationChar)) {

                equationHold += equationChar;

                if (i==(equation.length()-1)) {

                    stackNumbers.push(equationHold);    
                }

            } else {

                stackNumbers.push(equationHold);
                stackOperators.push(equationChar);
                equationHold = "";

            }

        }

I found it much easer than dealing with the String Split expressions. I'm not dealing with the brackets and stuff yet, so the code may change..

Pattern pp = Pattern.compile("\\d+");
Matcher m = pp.matcher("sdfsdf123sdfs3464ew111");
While(m.find())
{
    System.out.println(m.group());
}

output will be:

123
3464
111

check out !