Thread: Searching for words in a file

Good morning , i am writing a program that will wait for the user to enter a molecule , lets say he enters " h20" the program will go to a file search for the word and puts the weight name .. into an array , the problem is that i can't find a way on how to search for the "key word" or in our case "h20" , i want my program to search for this word an puts all of the line after h20 as an array . I hope you can help me guys thanks.
P.S : I just want a solution on how to find the key word and put the line after the key word in an array , because it may sound i need someone to do the program for me , i needed to clarify that , thanks.

" one of the String class's "
could you give me an example ? and are you sure it's the best way that is to divide the lines in lines ? Consider the file is too large isn't it wrong to consider the file as many lines and then to search our word?