CodeGym/Help with Java Tasks/Could somebody explain to me this task? I really didn't u...

Level 41

São Paulo

03.07.2020
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13comments

Could somebody explain to me this task? I really didn't understand anything about it...

Question about the task

Under discussion

It seems that I'm the only one who didn't get this one, and this is very frustrating. ¯\_(ツ)_/¯ Anyway, I tried to follow the steps of the requirements, but I really don't understand what this task is about, or what I have to do. I looked at the only two other help topics and still didn't get it... Any clarification would be very appreciated. Thanks! (Now I'm gonna cry in fetal position while I wait for an answer)

Implement FileConsoleWriter's logic.
The FileConsoleWriter class must have a private FileWriter field called fileWriter.
The FileConsoleWriter class must have every constructor used to initialize fileWriter for writing.
The FileConsoleWriter class must have five write methods and one close method:

public void write(char[] cbuf, int off, int len) throws IOException
public void write(int c) throws IOException
public void write(String str) throws IOException
public void write(String str, int off, int len) throws IOException
public void write(char[] cbuf) throws IOException
public void close() throws IOException

When writing data to a file, FileConsoleWriter must also write the data to the console.

Requirements:

The FileConsoleWriter class must contain a private FileWriter field called fileWriter that should not be initialized immediately.
The FileConsoleWriter class must have five constructors that initialize the fileWriter for writing.
The FileConsoleWriter class must have a write(char[] cbuf, int off, int len) throws IOException method, which should write data to fileWriter as well as the console.
The FileConsoleWriter class must have a write(int c) throws IOException method, which should write data to fileWriter as well as the console.
The FileConsoleWriter class must have a write(String str) throws IOException method, which should write data to fileWriter as well as the console.
The FileConsoleWriter class must have a write(String str, int off, int len) throws IOException method, which should write data to fileWriter as well as the console.
The FileConsoleWriter class must have a write(char[] cbuf) throws IOException method, which should write data to fileWriter as well as the console.
The FileConsoleWriter class must have a close() throws IOException method, which should call the corresponding method on fileWriter.

package com.codegym.task.task19.task1917; /* Your own FileWriter */ import java.io.FileWriter; import java.io.IOException; public class FileConsoleWriter { private FileWriter fileWriter; public static void main(String[] args) { } public FileConsoleWriter(char[] cbuf, int off, int len) throws IOException { fileWriter.write(cbuf, off, len); } public FileConsoleWriter(int c) throws IOException { fileWriter.write(c); } public FileConsoleWriter(String str) throws IOException { fileWriter.write(str); } public FileConsoleWriter(String str, int off, int len) throws IOException { fileWriter.write(str, off, len); } public FileConsoleWriter(char[] cbuf) throws IOException { fileWriter.write(cbuf); } public void write(char[] cbuf, int off, int len) throws IOException { } public void write(int c) throws IOException { } public void write(String str) throws IOException { } public void write(String str, int off, int len) throws IOException { } public void write(char[] cbuf) throws IOException { } public void close() throws IOException { } }

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KIN SOCHEAT

Level 34 , Phnom Penh, Cambogia

7 July 2020, 02:05

public void write(char[] cbuf, int off, int len) throws IOException { fileWriter.write(cbuf, off, len); for(int i = 0; i < len; i++) System.out.print(cbuf[off + i]); //why "off + i"? } public void write(String str, int off, int len) throws IOException { fileWriter.write(str, off, len); System.out.println(str.substring(off, off + len)); //why "off + len"? } ------i think : char[] cbuf, int off, int len : here(len) loop through array so you have to print out all arrays(ex: 1-10) String str, int off, int len : here (len) just one number no array so print out just a number (ex: 1)

Henrique

Level 41 , São Paulo, Brazil

7 July 2020, 16:03

Yeah... I did some tests and I finally got it. Thanks!!

KIN SOCHEAT

Level 34 , Phnom Penh, Cambogia

4 July 2020, 08:27

have you try Hanrique code?

Henrique

Level 41 , São Paulo, Brazil

6 July 2020, 13:33

Hey. In my response to Guadalupe, the constructors part is correct. The methods part is also correct, except for the method bellow, which should be:

public void write(String str, int off, int len) throws IOException {
	fileWriter.write(str, off, len);
	System.out.println(str.substring(off, off + len));
}

But I still don't understand why it must be "off + len" here, and "off + i" on the other method.

Henrique

Level 41 , São Paulo, Brazil

7 July 2020, 16:03

Ok, now I understand it all (I guess).

Guadalupe Gagnon

Level 37 , Tampa, United States

3 July 2020, 19:32

Lines 19-37 are constructors that are being used like methods. This should not be the case. The code here needs to include all the constructors that would initialize a FilerWriter object, and subsequently initialize the FileWriter on line 13. An example of constructor use:

String filename = "/*some file on your computer*/";
FileWriter temp = new FilerWriter(filename);
// this line uses the constructor that takes in a String of a file location to initialize the object

You have the methods that you need on lines 39-61, but no code. The code that was written erroneously in the constructors (where is said they are being used like methods) should go here in the methods.

Henrique

Level 41 , São Paulo, Brazil

3 July 2020, 19:41

Hey, Guadalupe, thanks for your answer. I'll have to read and read and read again to understand completely (if possible). For now, I'm reading and copying the codes written on the other help topics and trying to understand them. What I've written so far (and I'll ask you some things):

public class FileConsoleWriter {

	private FileWriter fileWriter;

    public static void main(String[] args) {

    }

    //CONSTRUCTORS

    public FileConsoleWriter(String name) throws IOException {
    	this.fileWriter = new FileWriter(name);
    }

    public FileConsoleWriter(String name, boolean append) throws IOException {
    	this.fileWriter = new FileWriter(name, append);
    }

    public FileConsoleWriter(File file) throws IOException {
    	this.fileWriter = new FileWriter(file);
    }

    public FileConsoleWriter(File file, boolean append) throws IOException {
    	this.fileWriter = new FileWriter(file, append);
    }

    public FileConsoleWriter(FileDescriptor fodeu) throws IOException {
    	this.fileWriter = new FileWriter(fodeu);
    }

    //METHODS

    public void write(char[] cbuf, int off, int len) throws IOException {
    	fileWriter.write(cbuf, off, len);
    	for(int i = 0; i < len; i++)
    		System.out.print(cbuf[off + i]);
    }

    public void write(int c) throws IOException {
    	fileWriter.write(c);
    	System.out.println(c);
    }

    public void write(String str) throws IOException {
    	fileWriter.write(str);
    	System.out.println(str);
    }

    public void write(String str, int off, int len) throws IOException {
    	fileWriter.write(str, off, len);
    	System.out.println(str.substring(off, len));
    }

    public void write(char[] cbuf) throws IOException {
    	fileWriter.write(cbuf);
    	for(char c : cbuf)
    		System.out.print(c);
    }

    public void close() throws IOException {
    	fileWriter.close();
    }
}

Henrique

Level 41 , São Paulo, Brazil

3 July 2020, 19:43

Questions: These constructors with "boolean append", "File file" and "FileDescriptor", where did they come from? I had to know that these where necessary? I never saw the class "FileDescriptor" before...

Guadalupe Gagnon

Level 37 , Tampa, United States

3 July 2020, 19:55

I figured it out originally by using IntelliJ. If you type this:

FileWriter temp = new FileWriter(

Once you get to the '(', in about a second IntelliJ will have a popup that gives all the different values that this constructor can take:

Here, on my intelliJ(see pic) it shows: 1) String fileName 2) String fileName, boolean append 3) File file 4) File file, boolean append 5) FileDescriptor fd 6) String fileName, Charset charset 7) String fileName, Charset charset, boolean append 8) File file, Charset charset 9) File file, Charset charset, boolean append

Henrique

Level 41 , São Paulo, Brazil

3 July 2020, 20:25

Oh, I see. I tried this with Eclipse IDE and the same was shown (picture).

So the constructors of FileConsoleWriter must be analogous to FileWriter constructors, so that we can initialize the "fileWriter" object in it? Ok, now the constructors part is clearer to me. -- Still, I'd like to ask you some things about the methods, if you don't mind. So this is what I understood about the methods: Each "write" method on FileConsoleWriter must call a equivalent "write" method of the FileWrite class. To do so, we must use the FileWriter object called "fileWriter". I think I understand most of the methods used, but I'm having a hard time with the ones with "off, len":

public void write(char[] cbuf, int off, int len) throws IOException {
	fileWriter.write(cbuf, off, len);
	for(int i = 0; i < len; i++)
		System.out.print(cbuf[off + i]); //why "off + i"?
}

public void write(String str, int off, int len) throws IOException {
	fileWriter.write(str, off, len);
	System.out.println(str.substring(off, off + len)); //why "off + len"?
}

I didn't check the task yet, so I don't know if this code is correct. But the others wrote like this, so it's probably correct or close to. Why do we have to write "off + i" in the first case and "off + len" in the second case? I've read everywhere that "off" is "offset", and I don't know exactly what this word means. I couldn't find a translation to Portuguese (my first language) that made sense to me. And "len" is the length of the array/string, right? Well, as you can see I still don't understand everything, but your help was crucial to put me on the right way to begin to underst

Henrique

Level 41 , São Paulo, Brazil

3 July 2020, 20:27

[the final part was cut haha] Well, as you can see I still don't understand everything, but your help was crucial to put me on the right way to begin to understand it. Thanks!!!!

Henrique

Level 41 , São Paulo, Brazil

7 July 2020, 16:03

Ok, now I understand it all (I guess).

Andrei

Level 41

11 February 2021, 08:27

I am posting this comment for others that might check your question and wonder about off+len and off + i. Let's take an example for why you need off + len: You have a string 10 chars long. you want to read 5 char (len) starting from char 4. If you have just off and len as the parameters of the substring, the reading in the substring would start at 4 (this being your first parameter off) and would end at 5 (this being your second parameter len) and the substring would actually be 1 character length. Remember the substring takes as parameters the starting and end point and determines itself the length. Whereas in the write method you specify the starting point and the length. Therefor, you need to add off to len as the second parameter of the substring so it actually reads the number of chars you need. ex: 12345678910 - off 4 len 5 Expected output: 45678 substring output with (4,5) as parameters: 4 substring output with (4, 5+4) as parameters: 45678 As for cbuff off+i . Off represented where you want to start the reading from the array and i is the increment to read the next element. Hope it makes sense!