Remove a certain character from a .txt file

Question

If I type

java DeleteX e < input.txt > output.txt

in the terminal, the code is supposed to remove a certain character (in this case e) from the input.txt file and then save the same text to a new file output.txt but all the es should be removed.

Ex: If the text in input.txt is as follows:

Hello! My name is John Doe.

The output.txt file should be:

Hllo! My nam is John Do.

But I don't get the spaces in output.txt. I get:

Hllo!MynamisJohnDo.

Code:

public class DeleteX{
public static void main(String []args){

String x = args[0]; // The character I want removed from the text
char X = x.charAt(0); // Transform the character from String to char

    while(! StdIn.isEmpty()){
        String line = StdIn.readString(); // The .txt file

        for( int i = 0; i < line.length(); i++){


            if( line.charAt(i) != X ){
                System.out.print(line.charAt(i));

            } // if             
        } // for
     } // while 
   } // main
} // class

where you're trying to read and write data into text file in your code? — Omore, Mar 28 '17 at 09:51
@javafan Take a look at the command line. Any printed output will go to `output.txt`. — RealSkeptic, Mar 28 '17 at 09:57
What does `StdIn.readString()` do? It's not part of the JRE. Are you sure it reads a line at a time? — slim, Mar 28 '17 at 10:00
We don't know what your `StdIn` class does. My guess is that `readString` reads the next string up to the next space. In which case, of course, it will not read the space itself. — RealSkeptic, Mar 28 '17 at 10:01
I agree, the problem is in `readString` since rest of the code works fine http://ideone.com/Uc2X03 — Rachit Magon, Mar 28 '17 at 10:02
https://ericlippert.com/2014/03/05/how-to-debug-small-programs/ -- specifically the thing to do here is to either to debug by putting a `println(line)` following `line = StdIn.readString()`, or (better) to step through execution with a debugger. — slim, Mar 28 '17 at 10:08

score 0 · Answer 1 · answered Mar 28 '17 at 09:54

0

I think a better way to do this is to use the replace method on the string.

like:

line = line.replace(x, "");

and then just print that out.

answered Mar 28 '17 at 09:54

Mubashar Abbas

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What if `x` is `.` ? – slim Mar 28 '17 at 10:24
what difference does that make? – Mubashar Abbas Mar 28 '17 at 10:35
Oops, actually the problem with yours is that it only replaces the first instance of `x`. So you might want `replaceAll()` -- but the first argument to `replaceAll(String,String)` is a regular expression. – slim Mar 28 '17 at 10:48
I just tried an example to make sure, and `replace` does replaces all occurences of `x` from the string. – Mubashar Abbas Mar 28 '17 at 12:24
My mistake - apologies. – slim Mar 28 '17 at 12:34

vlaxmi · Answer 2 · 2017-03-29T08:11:18.450

0

you can use String.replace method to replace the character. e.g.

String replaceString=s1.replaceAll(""+x,""); //replaces all occurrences of x to "".

e.g.

String input = "Hello! My name is John Doe.";
char X = 'e';
System.out.println(input.replaceAll("" + X, ""));

The output printed is - Hllo! My nam is John Do.

edited Mar 29 '17 at 08:11

answered Mar 28 '17 at 09:56

vlaxmi

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What is an "empty char"? – RealSkeptic Mar 28 '17 at 09:58
There is no "empty char"... `''`won't compile. You need `String#replace(String, String)` with `""` as second parameter – Stefan Warminski Mar 28 '17 at 10:01
I agree that it's easier to use the library implementation of replace than to write your own loop - but if OP uses this approach, they'll get the same result they already do, since their input string will still be missing spaces. – slim Mar 28 '17 at 10:06
what if occurrence of x is more than one in given string? – Omore Mar 28 '17 at 10:06
@slim str.trim() is also useful in this case. – Omore Mar 28 '17 at 10:35
As @MushabarAbbas points out above, `replace(String,String)` *does* replace all instances. Reverted my edit. – slim Mar 28 '17 at 15:28
thanks @slim. Not sure why the answer was down voted then – vlaxmi Mar 29 '17 at 00:59
@vlaxmi it doesn't actually solve the OP's problem; put `line.replace(...)` into their program instead of the loop, and it would still give a result with no spaces. – slim Mar 29 '17 at 08:03
@slim - For this code the result is as expected - String input = "Hello! My name is John Doe."; char X = 'e'; System.out.println(input.replaceAll("" + X, "")); this gives expected result. – vlaxmi Mar 29 '17 at 08:12
why was it down voted? the answer is correct as updated on above comment. Also attached output to the answer – vlaxmi Mar 29 '17 at 08:48
@vlaximi this isn't OP's problem. If `line == "Hello! My name is John Doe."` OP's loop would write `"Hllo! My nam is John Do."`. OP's problem is (probably) that `line` is `"Hello!"` then `"My"`, `"name"` etc. There is nothing wrong with OP's char-stripping loop, except that it could be replaced with a library method. But OP doesn't seem interested in following up, so this page is effectively dead. – slim Mar 29 '17 at 09:06

score 0 · Answer 3 · edited May 23 '17 at 12:02

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According to this page http://introcs.cs.princeton.edu/java/stdlib/javadoc/StdIn.html

the StdIn functions operate by reading tokens one at a time, where

A token is a maximal sequence of non-whitespace characters.

That means your call to StdIn.readString(); is not reading a line at a time, but a token (or word) at a time - by definition, without spaces.

So you should read a line at a time instead, instead of using StdIn. See Read input line by line

edited May 23 '17 at 12:02

Community

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answered Mar 28 '17 at 10:08

racraman

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You're probably right, but it's a bit of a guess whether this is the `StdIn` class OP is using. – slim Mar 28 '17 at 10:09

Remove a certain character from a .txt file

3 Answers3