Java - Check whether a number given by the user from console is in a text file

Question

I'm kinda new to Java so I'm looking for an help to do this.

As the title says, I'm trying to write a program that checks if a number given by the user from console is inside a text file with one number for each line or not.

I am using the Scanner class to check every line, but I am having problems with what condition the if statement should have when the number is found inside the file. I wrote down this part code (I'm not even sure if it's correct itself, so correct me if I'm wrong):

int lines = 0;
while (filescanner.hasNextLine()) {
    String line = filescanner.nextLine();
    lines++;
    if(conditon here) {
        System.out.println("I found the number on line " + lines);
    }
}

Thanks in advance.

`line.contains(value)` You might need to call the `toString()` method on the value — XtremeBaumer, Feb 12 '18 at 14:48
Where is the part where you let the user input the number ? How do you get the input ? — Exception_al, Feb 12 '18 at 14:58
@curlyBraces filescanner is a Scanner variable with argument the file variable previously declared(File file=new File() — David, Feb 12 '18 at 15:17
@Exception_al i let the user input the number with: int number; number=keyboard.nextInt(); the keyboard variable is another Scanner type(Scanner keyboard=new Scanner(System.in) — David, Feb 12 '18 at 15:20
Possible duplicate of [How do I convert a String to an int in Java?](https://stackoverflow.com/questions/5585779/how-do-i-convert-a-string-to-an-int-in-java) — rghome, Feb 12 '18 at 16:21

score 0 · Answer 1 · answered Feb 12 '18 at 15:25

0

Since you are getting the input number from Scanner keyboard, you can get its value like this:

String input = keyboard.next();

Then your if condition can be if(line.contains(input))

answered Feb 12 '18 at 15:25

curlyBraces

1,095
8
12

this really noice :) – STEEL Feb 13 '18 at 04:57

score 0 · Answer 2 · answered Feb 12 '18 at 16:17

You need to convert the line to an integer and then test it. If it is not an integer the parseInt method throws an exception.

try {
    int n = Integer.parseInt(line);
    if (n == number) {
        // found it
    }
} catch (NumberFormatException e) {
    // Not a number
}

Java - Check whether a number given by the user from console is in a text file

2 Answers2