如何检查文本文件中是否包含单个字符串或两个字符串？

Question

Lets say I have a text file which have two strings in each line:

New York 52.523405 13.4114
San Antonio 41.387917 2.169919
Los Angeles 51.050991 13.733634

and this is my code to split the string out from the line:

for (int i = 0; i < noOfStores;i++){
    nextLine = console.readLine();
    nextLine = nextLine.trim();
    String temp[] = nextLine.split(" ");
    String Word = temp[0] + " " + temp[1];
    storeNames[i] = firstWord;
    latitudes[i] = Double.parseDouble(temp[2]);
    longitudes[i] = Double.parseDouble(temp[3]);
}

but what if a text file contain only one string in each line like this:

Berlin 52.523405 13.4114
Barcelona 41.387917 2.169919
Dresden 51.050991 13.733634

How can I check whether a text file contain one or two string when reading it?

Answer 1

Use split(" ") , get the returned arrays length, and then parse the last two String array items in the array, items length - 1 and length - 2 , as doubles, and then iterate through the remaining String items prior to the last two items and combine them as the City String. Something like,

for (int i = 0; i < noOfStores;i++){
    nextLine = console.readLine();
    nextLine = nextLine.trim();
    String temp[] = nextLine.split(" ");
    int length = temp.length;
    if (length < 3) {
        // output is not as expected; throw some type of exception here.
    }
    latitudes[i] = Double.parseDouble(temp[length - 2]);
    longitudes[i] = Double.parseDouble(temp[length - 1]);

    // this should handle city names with 1, 2 or any number of tokens
    StringBuilder wordSb = new StringBuilder();
    for (int j = 0; j < length - 2; j++) {
       wordSb.append(temp[j]);
       if (j != length - 3) {
          wordSb.append(" ");
       }
    }
    storeNames[i] = wordSb.toString();
}

Answer 2

Use a regular expression.

String testData = "New York 52.523405 13.4114\n" +
                  "San Antonio 41.387917 2.169919\n" +
                  "Los Angeles 51.050991 13.733634\n" +
                  "Berlin 52.523405 13.4114\n" +
                  "Barcelona 41.387917 2.169919\n" +
                  "Dresden 51.050991 13.733634";

Pattern p = Pattern.compile("\\s*(.*?)\\s+(-?[0-9.]+)\\s+(-?[0-9.]+)\\s*");
try (BufferedReader in = new BufferedReader(new StringReader(testData))) {
    String line;
    while ((line = in.readLine()) != null) {
        Matcher m = p.matcher(line);
        if (! m.matches())
            throw new IllegalArgumentException("Bad data: " + line);
        String storeName = m.group(1);
        double latitude = Double.parseDouble(m.group(2));
        double longitude = Double.parseDouble(m.group(3));
        System.out.printf("Store '%s' is at %f, %f%n", storeName, latitude, longitude);
    }
}

Output

Store 'New York' is at 52.523405, 13.411400
Store 'San Antonio' is at 41.387917, 2.169919
Store 'Los Angeles' is at 51.050991, 13.733634
Store 'Berlin' is at 52.523405, 13.411400
Store 'Barcelona' is at 41.387917, 2.169919
Store 'Dresden' is at 51.050991, 13.733634

Answer 3

The most suitable tool for you task are regexps. As you can be sure that two of your numbers don't contain any spaces you can define them as "\\S+" , leaving anything else to be matched by pattern for name .

This allows you to have any number of words (and literally anything else) in name part, in the same time allowing to have numbers in any format (like scientific notation) as long as they don't have spaces inside.

String[] lines = new String[]{
        "New York 52.523405 13.4114",
        "San Antonio 41.387917 2.169919",
        "Los Angeles 51.050991 13.733634",
        "Berlin 52.523405 13.4114",
        "Barcelona 41.387917 2.169919",
        "Dresden 51.050991 13.733634",
        "Some scientific notation 1E-4 13.733634"
};

Pattern pattern = Pattern.compile("(.*)\\s+(\\S+)\\s+(\\S+)");

for (String line : lines) {

    Matcher matcher = pattern.matcher(line);
    if (matcher.matches()) {
        String name = matcher.group(1);
        double latitude = Double.parseDouble(matcher.group(2));
        double longitude = Double.parseDouble(matcher.group(3));

        System.out.printf("'%s', %.4f %.4f\n", name, latitude, longitude);
    }
}

Result:

'New York', 52.5234 13.4114
'San Antonio', 41.3879 2.1699
'Los Angeles', 51.0510 13.7336
'Berlin', 52.5234 13.4114
'Barcelona', 41.3879 2.1699
'Dresden', 51.0510 13.7336
'Some scientific notation', 0.0001 13.7336