CodeGym/Help with Java Tasks/Program run to Long!!!

Level 18

Surat

15.12.2018
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Program run to Long!!!

Question about the task

Sequential file output

Java Core, Level 6, Lesson 13

Under discussion

Where is the Problem?

1. Figure out what the program does.
2. In a static block, read 2 filenames: firstFileName and secondFileName.
3. Inside the Solution class, create a public static ReadFileThread class that implements the ReadFileInterface interface (Think about what is more appropriate: Thread or Runnable).
3.1. The setFileName method must set the name of the file whose contents will be read.
3.2. The getFileContents method must return the contents of the file.
3.3. In the run method, read the contents of the file and close the stream. Separate the lines of the file with spaces.
4. Think about where you need to wait for the thread to finish to ensure that the files are displayed sequentially.
4.1. To do this, add a call to the appropriate method.

Expected output:
[entire contents of the first file] [entire contents of the second file]

Requirements:

The Solution class's static block should read from the console the names of two files and store them in the variables firstFileName and secondFileName.
In the Solution class, declare the public static ReadFileThread class.
The ReadFileThread class must implement the ReadFileInterface interface.
The ReadFileThread class must inherit the appropriate class.
The ReadFileThread class's run method should read lines from the file set by the setFileName method. And the getFileContents method of this same class must return the file contents. The return value is one string consisting of the lines of the file, separated by spaces.
The systemOutPrintln method must call the join method on the created object f.
The program's output should consist of 2 lines. Each line contains the contents of one file.

package com.codegym.task.task16.task1630; import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.*; public class Solution { public static String firstFileName; public static String secondFileName; //write your code here static BufferedReader rd = new BufferedReader(new InputStreamReader(System.in)); static { try { firstFileName = rd.readLine(); secondFileName = rd.readLine(); } catch(IOException e) { } } public static void main(String[] args) throws InterruptedException{ systemOutPrintln(firstFileName); systemOutPrintln(secondFileName); } public static void systemOutPrintln(String fileName) throws InterruptedException{ ReadFileInterface f = new ReadFileThread(); f.setFileName(fileName); f.start(); //write your code here f.join(); System.out.println(f.getFileContents()); } public interface ReadFileInterface { void setFileName(String fullFileName); String getFileContents(); void start(); void join() throws InterruptedException; } //write your code here public static class ReadFileThread extends Thread implements ReadFileInterface { public String fileName = ""; public String line = ""; BufferedReader bfd; public void setFileName(String s) { fileName = s; try { bfd = new BufferedReader(new FileReader(fileName)); } catch(IOException e) { } } public String getFileContents() { return line; } public void run() { try { while(bfd!=null) { line += bfd.readLine(); } bfd.close(); } catch(Exception e) { } } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

24 December 2018, 17:02

#1 SetFileName is supposed to set the file name, not initialize a buffered reader.

public void setFileName(String s) {
      fileName = s;
      /*try {
          bfd = new BufferedReader(new FileReader(fileName));
      }
      catch(IOException e) {

      }*/
 }

Though i don't think this is why you are not able to verify. so on to the next: #2 This is an infinite loop:

while(bfd!=null)
{
      line += bfd.readLine();
}

I think you mean

while(bfd.ready())
{
      line += bfd.readLine();
}

Benjamin Winchester

Level 17 , Savannah, United States

5 January 2019, 05:18

On your #1 reply, you are incorrect, the BufferedReader must be initialized so the run function knows what file to read, deleting it means there is no link established to the file to be read. Additionally, on the line:

line += bfd.readLine()

you must add a delimiting space, so:

line += bfd.readLine() + " ";

this will verify.

Guadalupe Gagnon

Level 37 , Tampa, United States

5 January 2019, 17:09

Ben On #1 I already said i didn't think that was the problem. On my solution i just used the method to set the file name and then initialized the reader in the run method. Also the readline() method already separates what is read in with a new line character. You do not need to add (+ " "). His issue is the infinite loop.

jim smith

Level 22 , Cedar Park, United States

30 January 2019, 17:41

Thanks for the tip on the ready method. What I found though is the + " " is needed. Also you still need to set the fileName variable so the buffer reader knows what file to read. so above the while loop I have br = new BufferedReader(new FileReader(fileName));

Guadalupe Gagnon

Level 37 , Tampa, United States

30 January 2019, 18:40

Ya, it looks like you do in fact need the '+ " ", in there. I may have spoken a little too quickly.

Henk

Level 19 , Pretoria, South-Africa

30 May 2019, 08:24

hi Guadalupe thanks for always assisting us. Please tell me what the difference is between bfd!=null and bfd.ready() ? I used ready, but see other examples where they check if the line contains something (using null). See the link for example: https://www.tutorialspoint.com/java/io/bufferedreader_readline.htm Thank you!

Guadalupe Gagnon

Level 37 , Tampa, United States

30 May 2019, 14:06

@henk Checking if bfd is null or not is checking whether an object has been created. That line where they created an infinite loop reads while (bfd != null){ // this is checking if bfd has been initialized. If it has been it will alway be true. // do something } so:

BufferedReader bfd;  // at this point bfd would equal null
bfd = new BuffereReader(*other stuff*);
// at this point an object is created and bfd no longer equals null

bfd.ready() is a method of the buffered reader class that returns true if there are more data to be read, or false otherwise. If bfd == null, and you tried to call .ready() (or any method for that matter), a NullPointerExcpetion would be thrown.

Guadalupe Gagnon

Level 37 , Tampa, United States

30 May 2019, 14:12

The article you shared is showing that they are checking if the string is null or not:

String temp;  // creation of a blank string

while((temp = bfd.readline()) != null){
  // do something
}
// this is reading in a line and setting it to temp. It will execute
// first before checking if it is null because it is in parentheses
// (standard order of operation). When this line executes and
// temp == null, that means no data was read in, which means
// the data from source has been fully read in, and the loop ends.

This is the method that I have been using since about your level when I first encountered it. I think its elegant and easy to understand.

Henk

Level 19 , Pretoria, South-Africa

31 May 2019, 08:32

ok that makes absolute sense! thanks for the explanation!