JAVA 提取变量 substring

Question

I have a string array,"stringArray", with the following contents:

"ADU-30"
"ADU-30 plus a cam"
"ADU-30 plus internal cam"
"ADU-60"
"ADU-60 plus a cam"
"ADU-60 plus internal cam"
"ADU-301"

My goal is to be able to extract the "ADU-" portion including the numeric digits to the right of the hyphen. Currently, I can extract the ones with just two numeric digits to the right of the hyphen as follows:

for (int i = 0; i < stringArray.length(); i++) {
   stringArray[i] = stringArray[i].substring(0,6);
}

However, when I change the substring arguments from substring(0,6) to substring(0,7) , it crashes on the item with just two digits to the right of the hyphen. How can I store the three digits items? Also, is there a better way to do this then using substring? My desired end result is the following string array:

"ADU-30"
"ADU-60"
"ADU-301"

Answer 1

Keeping with your current pattern you could replace the hard-coded substring with a regex-based replaceAll (or replaceFirst ):

for (int i = 0; i < stringArray.length; i++) {
  stringArray[i] = stringArray[i].replaceAll("(ADU-\\d+).*", "$1");
}

This says to replace the whole string with the part, or group, that matches ADU-\\d+ , which is the string "ADU-" followed by 1 or more digits. The pattern after the capture group, ".*" just says to match zero or more charcters of any kind, which takes care of the, possibly empty, remainder of the string.

Test:

String[] stringArray = {
        "ADU-30",
        "ADU-30 plus a cam",
        "ADU-30 plus internal cam",
        "ADU-60",
        "ADU-60 plus a cam",
        "ADU-60 plus internal cam",
        "ADU-301"
        };

for (int i = 0; i < stringArray.length; i++) {
   stringArray[i] = stringArray[i].replaceAll("(ADU-\\d+).*", "$1");
}

for(String str : stringArray)
    System.out.println(str);

Output:

ADU-30
ADU-30
ADU-30
ADU-60
ADU-60
ADU-60
ADU-301

Answer 2

A "brute force" approach would be something like this:

for (int i = 0; i < stringArray.length; i++) {
        String s = stringArray[i];
        StringBuffer sb = new StringBuffer();
        for (int j = 0; j < s.length(); j++) {
                char c = s.charAt(j);
                if (c == ' ')
                        break;
                sb.append(c);
        }
        stringArray[i] = sb.toString();
}

Answer 3

Try using Java Pattern and Matcher class.

String[] stringArray = new String[] {"ADU-6022 plus a cam",
                                    "ADU-30",
                                    "ADU-30 plus a cam",
                                    "ADU-30 plus internal cam",
                                    "ADU-60",
                                    "ADU-60 plus a cam",
                                    "ADU-60 plus internal cam",
                                    "ADU-301"};
String regex = "(ADU-\\d+)";
Pattern p = Pattern.compile(regex);
Matcher m;

for (int i = 0; i < stringArray.length; i++) {
    m = p.matcher(stringArray[i]);
    while (m.find()) {
        System.out.println(m.group(1) );
    }
}

Answer 4

Use regex to extract the first group.

  // String to be scanned to find the pattern.
  String line = "ADU-30 plus a cam";
  String pattern = "^(ADU-\\d+).*$";

  // Create a Pattern object
  Pattern r = Pattern.compile(pattern);

  // Now create matcher object.
  Matcher m = r.matcher(line);

  if (m.find()) {
     System.out.println("Found value: " + m.group(0) );
  } else {
     System.out.println("NO MATCH");
  }

This pattern ^(ADU-\d+).*$ says:

1. Start at the beginning of the string ( ^ )

2. Capture "ADU" + some number of digits ( (ADU-\d+) )

3. Match anything until the end of the string ( .*$ )