[java] Get int from String, also containing letters, in Java

How can I get the int value from a string such as 423e - i.e. a string that contains a number but also maybe a letter?

Integer.parseInt() fails since the string must be entirely a number.

The NumberFormat class will only parse the string until it reaches a non-parseable character:

((Number)NumberFormat.getInstance().parse("123e")).intValue()

will hence return 123.

Perhaps get the size of the string and loop through each character and call isDigit() on each character. If it is a digit, then add it to a string that only collects the numbers before calling Integer.parseInt().

Something like:

    String something = "423e";
    int length = something.length();
    String result = "";
    for (int i = 0; i < length; i++) {
        Character character = something.charAt(i);
        if (Character.isDigit(character)) {
            result += character;
        }
    }
    System.out.println("result is: " + result);

Just go through the string, building up an int as usual, but ignore non-number characters:

int res = 0;
for (int i=0; i < str.length(); i++) {
    char c = s.charAt(i);
    if (c < '0' || c > '9') continue;
    res = res * 10 + (c - '0');
}

Replace all non-digit with blank: the remaining string contains only digits.

Integer.parseInt(s.replaceAll("[\\D]", ""))

This will also remove non-digits inbetween digits, so "x1x1x" becomes 11.

If you need to confirm that the string consists of a sequence of digits (at least one) possibly followed a letter, then use this:

s.matches("[\\d]+[A-Za-z]?")

You can also use Scanner :

Scanner s = new Scanner(MyString);
s.nextInt();