number out of string in java

Question

I have something like "ali123hgj". i want to have 123 in integer. how can i make it in java?

Answer 1

Use the following RegExp (see http://java.sun.com/docs/books/tutorial/essential/regex/):

\d+

By:

final Pattern pattern = Pattern.compile("\\d+"); // the regex
final Matcher matcher = pattern.matcher("ali123hgj"); // your string

final ArrayList<Integer> ints = new ArrayList<Integer>(); // results

while (matcher.find()) { // for each match
    ints.add(Integer.parseInt(matcher.group())); // convert to int
}

Answer 2

int i = Integer.parseInt("blah123yeah4yeah".replaceAll("\\D", ""));
// i == 1234

Note how this will "merge" digits from different parts of the strings together into one number. If you only have one number anyway, then this still works. If you only want the first number, then you can do something like this:

int i = Integer.parseInt("x-42x100x".replaceAll("^\\D*?(-?\\d+).*$", "$1"));
// i == -42

The regex is a bit more complicated, but it basically replaces the whole string with the first sequence of digits that it contains (with optional minus sign), before using Integer.parseInt to parse into integer.

Answer 3

You could probably do it along these lines:

Pattern pattern = Pattern.compile("[^0-9]*([0-9]*)[^0-9]*");
Matcher matcher = pattern.matcher("ali123hgj");
boolean matchFound = matcher.find();
if (matchFound) {
    System.out.println(Integer.parseInt(matcher.group(0)));
}

It's easily adaptable to multiple number group as well. The code is just for orientation: it hasn't been tested.

Answer 4

int index = -1;
for (int i = 0; i < str.length(); i++) {
   if (Character.isDigit(str.charAt(i)) {
      index = i; // found a digit
      break;
   }
}
if (index >= 0) {
   int value = String.parseInt(str.substring(index)); // parseInt ignores anything after the number
} else {
   // doesn't contain int...
}

Answer 5

public static final List<Integer> scanIntegers2(final String source) {
    final ArrayList<Integer> result = new ArrayList<Integer>(); 
    // in real life define this as a static member of the class.
    // defining integers -123, 12 etc as matches.
    final Pattern integerPattern = Pattern.compile("(\\-?\\d+)");
    final Matcher matched = integerPattern.matcher(source);
    while (matched.find()) {
     result.add(Integer.valueOf(matched.group()));
    }
    return result;

Input "asg123d ddhd-2222-33sds --- ---222 ss---33dd 234" results in this ouput [123, -2222, -33, -222, -33, 234]