Java: Numbers only String by removing non numeric characters

With Java, deleting non numeric characters (letters, symbols etc) from a string to produce a numbers-only String is a common requirement in web applications, as application users are used to insert numeric values with non-numeric characters.

For example a phone number will be entered with (-) characters like;
650-212-5710.
A price value may be entered with (,) characters like;
12,500.00

In Java, java.lang.Character class has a method; isDigit() which can be used to identify whether a character is a digit or not.

Following method can be used for extracting a numbers-only string, by removing all non-digits.

public static String getOnlyNumerics(String str) {
    
    if (str == null) {
        return null;
    }

    StringBuffer strBuff = new StringBuffer();
    char c;
    
    for (int i = 0; i < str.length() ; i++) {
        c = str.charAt(i);
        
        if (Character.isDigit(c)) {
            strBuff.append(c);
        }
    }
    return strBuff.toString();
}

Calling above method with any String will return a numbers-only string.

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