Last Condition: "The output must contain the contents of the first file."

Question about the task

Under discussion

There's several layers to this question: 1) This sounds ignorant to ask at this point, but how in the heck does one use the console interface in IntelliJ? That would seem useful here. (As opposed to CodeGym where it's just "there".) 2) Since I can't play with any file names on the console interface, it makes it difficult for me to check my work. Any insights wiser minds than my own can contribute here would be greatly appreciated! : )

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.*; public class Solution { public static String firstFileName; public static String secondFileName; //write your code here //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. static{ try { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); firstFileName = reader.readLine(); secondFileName = reader.readLine(); }catch(IOException e){ } } public static void main(String[] args) throws InterruptedException { //The program's output should consist of 2 lines. Each line contains the contents of one file. systemOutPrintln(firstFileName); systemOutPrintln(secondFileName); } public static void systemOutPrintln(String fileName) throws InterruptedException { //The systemOutPrintln method must call the join method on the created object f. ReadFileInterface f = new ReadFileThread(); f.setFileName(fileName); f.start(); //write your code here System.out.println(f.getFileContents()); f.join(); } public interface ReadFileInterface { void setFileName(String fullFileName); String getFileContents(); void join() throws InterruptedException; void start(); } //write your code here //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. public static class ReadFileThread extends Thread implements ReadFileInterface { String fullFileName; StringBuffer fileContents = new StringBuffer(""); //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. @Override public void run(){ //The run() method does the work of getting the data from the file and constructing the string line by line. The getFileContents just returns the string or an empty string if it's null. FileInputStream fileReader = null; String fileLineReader = ""; try { fileReader = new FileInputStream(fullFileName); }catch(FileNotFoundException e){ } BufferedReader fileBufferedReader = new BufferedReader(new InputStreamReader(fileReader)); try { while((fileLineReader = fileBufferedReader.readLine()) != null){ fileContents.append(fileLineReader + " "); } }catch(IOException e){ } try { fileReader.close(); fileBufferedReader.close(); }catch(IOException e){ } } @Override public void setFileName(String fullFileName) { //Not sure about this, but I'm not sure what else would be going on here. this.fullFileName = fullFileName; } @Override public String getFileContents() { return fileContents.toString(); } /*@Override //I'm not sure about the join(). It won't let me write new implementation for it if I inherit the Thread class since it's //final in the Thread class. But I'm confused why it's declared in the ReadFileInterface then. public void join() throws InterruptedException { }*/ } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

1 February 2023, 19:05

useful

The console is at the bottom when you run a program in intelliJ:

Before I am ready to pass in I use hard coded tests for debugging purposes. Either the file names... or the file contents. So instead of reading from the console the file name you can just do this:

firstFileName = "path to first file here";
secondFileName = "path to second file here";

Just be sure to change it to what the task requires once you have an adequate solution and are ready to try validation. Methods that are inherited from an interface (that are not default) MUST be implemented in the class that inherits that interface. If the method is defined and also inherited from a parent class this does not mean that you need to create a whole new method in the child class that inherits that interface, such as the case in your notes on this task.

Guadalupe Gagnon

Level 37 , Tampa, United States

1 February 2023, 19:05

useful

One problem that I can identify with your solution is that the join() method is called in the incorrect location. In this task there are going to be three threads (one thread to run the code and 2 threads created in the code). The first thread is actually the thread that is started when the "run" button is pressed. It starts in the static block and runs lines 11-21 then goes to the main() method at line 24, moves to 25, reaches line 26 which calls the systemOutPrintln() method which sends it to line 30. It then creates and starts a new thread by line 34. If you remember threads run at the same time by the CPU switching intermittently between them. This means the new thread starts running in the run() method at line 63, but you have original "main" thread moving to line 37 at the same time. Line 37 is a Sys.out.prln() statement that tries to output the result of the run method. As the run method is still working most likely, though threads run randomly so its possible the run method could be finished, it is likely that the reading of the file contents will be incomplete and very little will be output. By calling join() on a thread, this case 'f', you are telling the thread reading the line (the "main" thread in this case) that it should wait until the thread 'f' completes. By moving the join() call to before line 37 means that the main thread will stop and wait for the 'f' thread to complete before line 37 outputs the full result. It would then bounce back to line 26, move to line 27, and repeat the process. Sorry for the wall of text. I hope that all makes sense

Mike S

Level 28 , Saint Louis, United States

1 February 2023, 19:27

It does and that tip for hardcoding a filename from my Desktop works great. The output appears just as it should. Yeah, I was just foolishly moving .join() but I admire your very careful reasoning. A lot of the other comments for this exercise on why the last requirement isn't passing had to do with extra spaces. That's not the case with mine though : / Thank you for the extra comment on overriding interface methods as well.

Mike S

Level 28 , Saint Louis, United States

1 February 2023, 19:47

I did it Guadalupe! I just needed to get rid of that last space dangling off of the end like you pointed out for others. Thank you! May not have won the award for the best code by IntelliJ, but I hung in there : )

Guadalupe Gagnon

Level 37 , Tampa, United States

1 February 2023, 20:19

I don't know if you have come across any of my help wanted posts, but in 2019 and 2020 my code wasn't all that compact and/or "intelligent". I have one more tip for you that I use that prevents the last empty space: Start by creating the first bit (like a line) of data, then every subsequent bit of data start with the breaking sequence (like the space). Example in your code, use this for lines 75-77:

// start with first bit of data
fileContents.append(fileBufferedReader.readLine());

// then do each subsequent bits with the breaking char or sequence
while((fileLineReader = fileBufferedReader.readLine()) != null){
    fileContents.append(" " + fileLineReader);
}

or another example, if you want to output the contents of a list with each value on a new line:

public class Solution {
    public static void main(String[] args) {
        List<Integer> temp = new ArrayList<>();
        temp.add(5); temp.add(7); temp.add(2); temp.add(15);

        System.out.println(createString(temp));
    }

    private static String createString(List list) {
        if(list.size() < 1) return "";
        StringBuilder sb = new StringBuilder();

        int i = 0;

        // add first bit
        sb.append(list.get(i++));

        // all subsequent bits start with breaking sequence
        for(;i < list.size(); i++)
            sb.append("\n").append(list.get(i));

        return sb.toString();
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

1 February 2023, 20:24

By using a generic List as the parameter for that createString() method it will output any list you pass to it no matter the type or the contained value. Programming abstractly like this is an important concept of Java. For example I could pass it a LinkedList<Character> or a Stack<String>.

Mike S

Level 28 , Saint Louis, United States

3 February 2023, 17:48

Thank you Guadalupe for the free tips!