How to extract words from a string in Java

Question

I've imported a file and turned it into a String called readFile. The file contains two lines:

qwertyuiop00%
qwertyuiop

I have already extracted the "00" from the string using: String number = readFile.substring(11, 13);

I now want to extract the "ert" and the "uio" in "qwertyuiop" When I try to use the same method as the first, like so:

String e = readFile.substring(16, 19);
String u = readFile.substring(20, 23);

and try to use:

System.out.println(e + "and" + u);

It says string index out of range.

How do I go about this? Is it because the next two words I want to extract from the string are on the second line? If so, how do I extract only the second line? I want to keep it basic, thanks.

UPDATE: it turns out only the first line of the file is being read, does anyone know how to make it so it reads both lines?

Answer 1

If you count the total number of characters for each string, they are more than the indexes your entering.

qwertyuiop00% is 13 characters. Call .length() method on the string to verify the length is the one you expect.

I would debug with adding the following before:

System.out.println(readFile);
System.out.println(readFile.length());

Note:

qwertyuiop00% qwertyuiop is 24 characters since space counts as a character. Unless ofcourse you don't have the space in which it's 23 characters and your indexes are 0 to 22

Note2:

I asked for the parser code since I suspect your using the usual code which is something like:

while ((line = reader.readLine()) != null)

You need to concatenate those lines into one String (though it's not the best approach).

see: How do I create a Java string from the contents of a file?

Answer 2

First split your string into lines, you could do this using

String[] lines = readFile.split("[\r\n]+");

You may want to read the content directly into a List<String> using Files.#readAllLines instead.

second, do not use hard coded indexes, use String#indexOf to find them out. If a substring does not occur in your original string, then the method retunrs -1 , always check for that value and call substring only when the return value is not -1 (0 or greater).

if(lines.length > 1) {
    int startIndex = lines[1].indexOf("ert");
    if(startIndex != -1) {
        // do what you want
    }
}

Btw, there is no point in extracting already known substring from a string

System.out.println(e + "and" + u);

is equivalent to

System.out.println("ertanduio");

Knowing the start and end position of a fixed substring makes only sence if you want to do something with rest of original string, for example removing the substrings.

Answer 3

You may give this a try:-

Scanner sc=new Scanner(new FileReader(new File(The file path for readFile.txt)));
String st="";
while(sc.hasNext()){
st=sc.next();
}
System.out.println(st.substring(2,5)+" "+"and"+" "+st.substring(6,9));

Check out if it works.