Styjun

Given a String that lists metadata about a book line by line, how do I print out only the lines that match the data I am looking for?

In order to do this, I've been trying to create substrings for each lines using indexes. The substring starts at the beginning of a line and ends before a "n". I have not seen lists, arrays or bufferedReader yet.

For each substring that I parse through, I check if it contains my pattern. If it does, I add it to a string that only includes my results.

Here would be an example of my list (in french); I'd like to match, for say, all the books written in 2017.

Origine D. Brown 2017 Thriller Policier

Romance et de si belles fiancailles M. H. Clark 2018 thriller policier Romance

La fille du train P. Hawkins 2015 Policier

There is a flaw in how I am doing this and I am stuck with an IndexOutOfBounds exception that I can't figure out. Definitely new in creating algorithms like this.

public static String search() 
 String list;

 int indexLineStart = 0;
 int indexLineEnd = list.indexOf("n");
 int indexFinal = list.length()-1;
 String listToPrint = "";

 while (indexLineStart <= indexFinal)
 String listCheck = list.substring(indexLineStart, indexLineEnd);
 if (listCheck.contains(dataToMatch))
 listToPrint = listToPrint + "n" + listCheck;
 
 indexLineStart = indexLineEnd +1 ;
 indexLineEnd = list.indexOf("n", indexLineStart);

 

 return listeToPrint; 
 

Regardless of the comments about using split() and String[], which do have merit :-)

The IndexOutOfBounds exception I believe is being caused by the second of these two lines:

 indexLineStart = indexLineEnd +1 ;
 indexLineEnd = list.indexOf("n", indexLineStart);

You wan't them swapped around (I believe).

You don't have to make this much complex logic by using String.substring(), what you can use is String.split() and can make an array of your string. At each index is a book, then, you can search for you matching criteria, and add the book to the finalString if it matches your search.

Working Code:

public class stackString

 public static void main(String[] args)
 
 String list = "Origine D. Brown 2017 Thriller Policiern Romance et de si belles fiancailles M. H. Clark 2018 thriller policier Romancen La fille du train P. Hawkins 2015 Policiern";
 String[] listArray = list.split("n"); // make a String Array on each index is new book
 String finalString = ""; // final array to store the books that matches the search
 String matchCondition = "2017";
 for(int i =0; i<listArray.length;i++)
 if(listArray[i].contains(matchCondition))
 finalString += listArray[i]+"n";

 System.out.println(finalString);
 
 

Here is a solution using pattern matching

 public static List<String> search(String input, String keyword)
 
 Pattern pattern = Pattern.compile(".*" + keyword + ".*");
 Matcher matcher = pattern.matcher(input);
 List<String> linesContainingKeyword = new LinkedList<>();
 while (matcher.find())
 
 linesContainingKeyword.add(matcher.group());
 
 return linesContainingKeyword;
 

Since I wasn't allowed to use lists and arrays, I got this to be functional this morning.

 public static String linesWithPattern (String pattern){
 String library;
 library = library + "n"; //Added and end of line at the end of the file to parse through it without problem.
 String substring = "";
 String substringWithPattern = "";
 char endOfLine = 'n';
 int nbrLines = countNbrLines(library, endOfLine); //Method to count number of 'n'
 int lineStart = 0;
 int lineEnd = 0;

 for (int i = 0; i < nbrLines ; i++)
 lineStart = lineEnd;
 if (lineStart == 0)
 lineEnd = library.indexOf('n');
 else if (lineStart != 0)
 lineEnd = library.indexOf('n', (lineEnd + 1));
 
 substring = library.substring(lineStart, lineEnd); 
 if (substring.toLowerCase().contains(motif.toLowerCase()))
 substringWithPattern = substring + substringWithPattern + 'n';
 
 if (!library.toLowerCase().contains(pattern.toLowerCase()))
 substringWithPattern = "nNO ENTRY FOUND n";

 
 
 if (library.toLowerCase().contains(pattern))
 substringWithPattern = "This or these books were found in the library n" +
 "--------------------------" + substringWithPattern;
 

 return substringWithPattern;

The IndexOutOfBounds exception is thrown when the index you are searching for is not in the range of array length. When I went through the code, you are getting this exception because of below line execution where probably the indexLineEnd value is more than the actual length of List if the string variable list is not Null (Since your code doesn't show list variable to be initialized).

String listCheck = list.substring(indexLineStart, indexLineEnd);

Please run the application in debug mode to get the exact value that is getting passed to the method to understand why it throwing the exception.

you need to be careful at calculating the value of indexLineEnd.