CodeGym/Help with Java Tasks/Baffling requirements.......

Level 37

Tampa

14.12.2018
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Baffling requirements.......

Question about the task

Resolved

This problem makes no sense. I have the slightest idea what is being asked for the three requirements I can not pass. Am i over thinking this, or is there missing information in the instructions/starting code?

Change the TableInterfaceWrapper class so that it wraps TableInterface.
The setModel method should display the number of elements in the new list before updating the model.
The getHeaderText method should return the text in upper case. Use the toUpperCase() method.

Requirements:

The TableInterfaceWrapper class must implement the TableInterface interface.
The TableInterfaceWrapper class must initialize a TableInterface field in the constructor.
The setModel() method should display the number of elements in the new list before updating the model.
The getHeaderText() method must return the text in uppercase.
The setHeaderText() method must set the header text without making changes.

package com.codegym.task.task18.task1815; import javax.swing.*; import javax.swing.event.ListDataListener; import java.util.List; /* Table */ public class Solution { public class TableInterfaceWrapper implements TableInterface { TableInterface component; String headerText; public TableInterfaceWrapper(TableInterface component) { this.component = component; } public void setModel(List rows) { System.out.println(rows.size()); } @Override public String getHeaderText() { return headerText.toUpperCase(); } @Override public void setHeaderText(String newHeaderText) { headerText = newHeaderText; } } public interface TableInterface { void setModel(List rows); String getHeaderText(); void setHeaderText(String newHeaderText); } public static void main(String[] args) { } }

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Oliver Heintz

Level 18 , Mustang, United States

12 March 2021, 21:26

Even when you're not helping me, you're helping me. I couldn't figure out why my getHeaderText requirement was failing, but reading through these comments I was able to fix the issue.

Guadalupe Gagnon

Level 37 , Tampa, United States

12 March 2021, 21:30

This task made zero sense to me back when I first encountered it and was new to Java. Even after I solved it I only half understood it. It makes more sense the more you know about OOP techniques and how interfaces are to be used effectively. If you have a Java book, jump to the section on interfaces.

Oliver Heintz

Level 18 , Mustang, United States

14 March 2021, 01:46

See, I understood the parts about interfaces just fine. They're basically classes, but completely abstract, which means you have to implement all the methods of the interface. I'm not understanding why I had to have some TableInterface component. I'm not even sure what that means. It's not an object, right, because nothing is created (there is no new keyword). So it's a variable that is declared? It points at an object, but it hasn't been assigned one? But then we initialize it when we call on the TableInterfaceWrapper constructor? Which then allows us to use it in the methods we've overridden, as in: return component.getHeaderText().toUpperCase(Locale.ROOT);

Guadalupe Gagnon

Level 37 , Tampa, United States

14 March 2021, 17:40

In this task it is pretending that you have an interface that does something.. this TableInterface. It is saying that this "something" that it does is most of what you need it to do, but not all. In this case you can create your own class that wraps the interface and provides the extra functionality that you have. Forget about trying to figure out what the table interface does, its abstract in this task, and just focus on the additional things the task you are to add in. By the way, this is commonly done in Java, and an example of it in use would be the BufferedReader class. I am sure you have used this line plenty of times:

BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

BufferedReader takes in a class that implements the Reader interface, such as an InputSreamReader. You can also pass in FileReader, StringReader, CharArrayReader etc. This gives you more, and very useful, functionality that the original object being wrapped does not have. Inside the BufferedReader class it would look similar to this task:

class BufferedReader {
     Reader component;

     public BufferedReader (Reader x) {
           component = x;
     }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

14 March 2021, 17:45

Additionally, using an interface provides much greater versatility than using a class. Imagine if the BufferedReader only took a class, say an InputStreamReader. Then it would only work with that one class. You couldn't use the BufferedReader for something like a FileReader. In this case you would have to create 2 different BufferedReaders, one for an InputStream and one for a File Reader; and more for every type of Reader there is. You could even create your own classes that implement the Reader interface and pass them to the BufferedReader class to wrap.

Guadalupe Gagnon

Level 37 , Tampa, United States

31 March 2020, 13:26

solution

Here is an example for everyone. If I wanted to wrap a Reader object, I would it with this code:

// reader is an interface
public class Solution extends Reader {
    Reader component;

    // To use this we need an actual reader, e.g. FileReader, InputStreamReader etc
    public Solution(Reader component) {
        this.component = component;
    }

    // pass off all the work to the 'component'
    public int read() throws IOException {
        System.out.println("Reading an int");
        return component.read();
    }

    public boolean ready() throws IOException {
        System.out.println("Checking if component is ready");
        return component.ready();
    }

    public int read(char[] cbuf, int off, int len) throws IOException {
        System.out.println("Something");
        return component.read(cbuf, off, len);
    }


    public void close() throws IOException {
        System.out.println("Now CLosing");
        component.close();
    }
   // used in code:
    public static void main(String[] args) throws Exception{
        FileReader temp = new FileReader("C:\\pathToSomeFile");
        Solution myReader = new Solution(temp);
        while(myReader.ready()){
            System.out.println(myReader.read());
        }
        myReader.close();
    }
}

In the above code I take in a reader in the constructor of my class, then use that component to actually do the work instead of me coding in all instructions to read from a source. The only extra functionality added is output lines in each method, though you can have it do anything that you need or can imagine. This is very useful. I wrap Lists all the time in my code to provide more functionality than the generic java Lists can do, such as having the toString() output more specific information.

Dedcom

Level 19 , Lahore, Pakistan

31 March 2019, 12:03

What to do in the setModel method???

Guadalupe Gagnon

Level 37 , Tampa, United States

31 March 2019, 20:05

Just add component.setModel(list);

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 20:13

I did solve this: Basically the constructor takes a tableInterface. Interfaces can not be made into objects, however classes that implement them can, so what would be passed into this would be a class that implements tableInterface. The methods should do what the task requirements say, but delegate everything else to the object saved as the initialized tableInterface. So for setHeaderText, the code only has to delegate it to the object like so:

public void setHeaderText(String headerText)
{
   tableInterface.setheaderText(headerText);
}

and then when you are supposed to do something according to the task, the code would be:

public String getHeaderText()
{
   return tableInterface.getHeaderText().toUpperCase();
}

No need to add properties other than the TableInterface object.

+29

Tumelo Mohlala

Level 35 , Johannesburg, South Africa

25 April 2019, 05:05

Guadalupe Gagnon, you sir are a superstar, thanks for the great help throughout this amazing course.

+14

Boris the Llama

Level 20 , Maidstone, United Kingdom

18 September 2019, 21:26

Without Guadalupe, I think I would have been stuck 10 lessons ago.

Guadalupe Gagnon

Level 37 , Tampa, United States

19 September 2019, 16:18

I failed most of these tasks multiple times before figuring them out. Lots of trial and error for me personally (and google).

matemate123

Level 50 , Kraków, Poland

22 January 2023, 16:22

Google is useless for students code gym after you step here and cleary explaining everything, thanks a lot! You have big influence for my educating here!

Guadalupe Gagnon

Level 37 , Tampa, United States

23 January 2023, 14:17

😂

jim smith

Level 22 , Cedar Park, United States

31 January 2019, 20:05

I got exactly to where you did before looking here for help.

Przemysław Dr

Level 20 , Tricity, Poland

19 March 2020, 15:58

Me too... That means that requirement are not clear enough...

Guadalupe Gagnon

Level 37 , Tampa, United States

19 March 2020, 17:48

This task is actually very easy, but at this point wrapper classes were a complete mystery. Come back to this in 6 months and you will see how simple this actually is.