Checking a Sub String in a String of a very large file ?

Question

Hi All,
I am having a 20mb file and i am coverting that 20mb file to a string.now i like to search whether the following substring appears in the string
a) One
b) Two
c) Three
I am just checking with String.indexOf() for each .
Is there is any other efficient way of searching this rather than the above method String.indexOf
please give me some suggestion how to perform searching in a very large string.
Thanks,
J.Kathir

Answer 1

We have to read line and check for the three strings
right ?
Is there is any other way to check the substring in
the whole string ?
Reading line by line and searching for the three
strings or Reading the entire file as string and
searching for the substring
which is better ?Depends on your definition of "better" - reading line by line saves memory, but is probably slower. Reading the entire file into memory then searching it is probably faster but takes more memory.
As a third option, if you're using version 1.5, you can use the Scanner class to read the file and search for all 3 strings at the same time...something like this:
Scanner scn = new Scanner(new File("myfile.txt"));
String regExp = "a|b|c";
String s;
while ((s = scn.findWithinHorizon(regExp)) != null) {
  System.out.println("Found: " + s);
scn.close();I'm pretty sure this is more efficient as it looks for anything matching the regular expression as it goes through the String...but I haven't done any timings on each approach.