Optimal way to find if a string is present in a file

Question

I have a text file containing thousands of lines. What would be the optimal way to find if a certain string exists in the file or not?

Either by reading the whole file into a string & then using string.contains method or by creating a list of all the lines using Files.readAllLines method & then looping through each line from the list & check whether that line contains the required string or not?

Update: I am using Java 7. The search is limited to 1-2 string searches per file(10 files).The string to be searched changes with the file. I want to stop the search if the string is found.

Answer 1

Since the file is containing a lot of lines, it will be better idea to read that file line-by-line, instead of getting all of it's content into program memory. So essentially, read one line check for presence of your string and move forward.