Enclosing Class

[BuckGup]

I am trying to reference an enclosing class in a program I am writing in Java. So far I have 

sr = new SortRunnable(SELECTION_SORT_TEXT, arr, SelectionSort.this;

SortRunnable is 

public SortRunnable(String sortingAlgorithm, int[] arr, Sorter sorter) {
        this.sortingAlgorithm = sortingAlgorithm;
        this.arr = arr;
        this.sorter = sorter;
    }

and SelectionSort is 

public class SelectionSort {
	private static void sort(int arr[]) {
        int n = arr.length;

        // One by one move boundary of unsorted subarray
        for (int i = 0; i < n-1; i++) {
            // Find the minimum element in unsorted array
            int min_idx = i;
            for (int j = i+1; j < n; j++) {
                if (arr[j] < arr[min_idx]) {
                    min_idx = j;
                }
            }

            // Swap the found minimum element with the first
            // element
            int temp = arr[min_idx];
            arr[min_idx] = arr[i];
            arr[i] = temp;
        }
    }
}

but it keeps saying 'SelectionSort' in not an enclosing class.

 

Aren't I referencing the sort inside SelectionSort by doing SelectionSort.this?

 

[2FA]

If that's exactly what you have, and SortRunnable is the inner class, then you're missing the class keyword on it. You're also missing the ')' after this.

 

EDIT: honestly there is context missing here in general so it's hard to see what is wrong, as you don't show both classes.

Looking at it, SortRunnable is a constructor but you don't show the actual class structure.

[2FA]

Shouldn't it be this?

SelectionSort ss = new SelectionSort();
SelectionSort.SortRunner sr = ss.new SortRunner(SELECTION_SORT_TEXT, arr, SelectionSort.this);

 

[MrMG]

I am not really sure what you are trying to do.

But one problem I think is the fact that your SelectionSort class does not inherit from Sorter class:

public class SelectionSort {

But your Constructor of the SortRunnable class is looking for a Sorter object:

public SortRunnable(String sortingAlgorithm, int[] arr, Sorter sorter) {

And you are just entering a SelectionSort object:

sr = new SortRunnable(SELECTION_SORT_TEXT, arr, SelectionSort.this;

and you are also missing a ")" after SelectionSort.this .

 

[wasab]

Well, is SelectionSort an enclosing class? SelectionSort.this is only valid when "this" references a class embedded within SelectionSort

 

Eg.

Spoiler

Class outter{

     Class inner{

           // outter.this then references outter class which this inner is nested. 

      }

}

Note, if inner class is declared static, it will have the same restriction as any other static members. It will not be able to access nonstatic method and variables of its outter class. 

[BuckGup]

7 hours ago, wasab said:

Well, is SelectionSort an enclosing class? SelectionSort.this is only valid when "this" references a class embedded within SelectionSort

 

Eg.

  Reveal hidden contents

Class outter{

     Class inner{

           // outter.this then references outter class which this inner is nested. 

      }

}

Note, if inner class is declared static, it will have the same restriction as any other static members. It will not be able to access nonstatic method and variables of its outter class. 

So how do you call a sorte then? They are in the same package and all have the same design of having a static sort inside

7 hours ago, MrMG said:

I am not really sure what you are trying to do.

But one problem I think is the fact that your SelectionSort class does not inherit from Sorter class:

public class SelectionSort {

But your Constructor of the SortRunnable class is looking for a Sorter object:

public SortRunnable(String sortingAlgorithm, int[] arr, Sorter sorter) {

And you are just entering a SelectionSort object:

sr = new SortRunnable(SELECTION_SORT_TEXT, arr, SelectionSort.this;

and you are also missing a ")" after SelectionSort.this .

 

That was a copy and paste error the ) is back and still no go. What am I suppose to pass in it then?

8 hours ago, 2FA said:

Shouldn't it be this?

SelectionSort ss = new SelectionSort();
SelectionSort.SortRunner sr = ss.new SortRunner(SELECTION_SORT_TEXT, arr, SelectionSort.this);

 

That didn't work

 

Here is more code

public class SortRunnable implements Runnable {

    private String sortingAlgorithm;
    private int[] arr;
    private Sorter sorter;

    public SortRunnable(String sortingAlgorithm, int[] arr, Sorter sorter) {
        this.sortingAlgorithm = sortingAlgorithm;
        this.arr = arr;
        this.sorter = sorter;
    }

    @Override
    public void run() {
        long startTime;
        long endTime;
        startTime = System.currentTimeMillis();

        



       // sorter.displayResult();


    }
}

 

[colonel_mortis]

15 minutes ago, BuckGup said:

So how do you call a sorte then? They are in the same package and all have the same design of having a static sort inside

If you want to be able to choose the implementation, you can't use static methods. Static methods are looked up at compile time, so you can't call it based on a parameter (without reflection, but don't go there).

To call a static method, you would use SelectionSort.sort(...), but because you want to pass the implementation in you need to create an interface or abstract class which defines the sort method, then each implementation should implement that interface/extend the class.

 

I've built up a simple working example based on your code

(repl.it embeds are currently only available for admins, sorry)

Click the page button to show the files - I've added Sorter.java and modified SelectionSort.java to make it implement the Sorter interface.

[wasab]

4 hours ago, BuckGup said:

So how do you call a sorte then? They are in the same package and all have the same design of having a static sort inside

That was a copy and paste error the ) is back and still no go. What am I suppose to pass in it then?

That didn't work

 

Here is more code

public class SortRunnable implements Runnable {

    private String sortingAlgorithm;
    private int[] arr;
    private Sorter sorter;

    public SortRunnable(String sortingAlgorithm, int[] arr, Sorter sorter) {
        this.sortingAlgorithm = sortingAlgorithm;
        this.arr = arr;
        this.sorter = sorter;
    }

    @Override
    public void run() {
        long startTime;
        long endTime;
        startTime = System.currentTimeMillis();

        



       // sorter.displayResult();


    }
}

 

Well, you would pass an instance of a class into the static method to access it's members. The thing about static nested class is that an instance of an outter class does not need to exist just like if you use a static method, an instance of its class might not exist so there is no guranteed there is an instance of the class for you to invoke those none static methods or access member variables.

 

That is besides the point though. You don't need static everywhere and you seem to be abusing static quite a bit. I mean sure it is convenient because you don't need to deal with object instantiation and allow you to avoid OOP but if are determine to not use objects, then you really ought to be picking a programming language other than java. 

 

In your case, make sure that 

SortRunnable(SELECTION_SORT_TEXT, arr, SelectionSort.this);

is inside a nested class which is inside the SelectionSort class then there shouldn't be an error. You need to first instantiate selection sort class first. Instead of declaring nested class public, you should use a getter like you would for instance variables. 

 

E.g.

Spoiler

Class SelectionSort{

     public SortRunnable getNewSortRunnable(){

          return new SortRunnable("super alogrithm", new int[10], this); // change these parameters to whatever you need. 

     }

 

    private class SortRunnable implements Runnable{

 

           public SortRunnable(String sortingAlgorithm, int[] arr, SelectionSort sorter){

               //Do what need with the parameters

           }

         

          @override

           public void run(){

              // Do what you need with the interface method.

          }

 

        

 

   }

 

}

Then you can first instantiate Selection Sort then call on getNewSortRunnable to get an instance of inner class then do what you need to do from here.

 

E.g.

Spoiler

SelectionSort SSobj = new SelectionSort();

 

SortRunnable SRObj = SSobj.getNewSortRunnable();

 

Sorry if the code is sloppy. Im typing this on a phone. 

 

Edit, you don't need SelectionSort.this because as an inner class, SortRunnable already can access all the fields of the SelectionSort.

 

 

[BuckGup]

8 hours ago, colonel_mortis said:

If you want to be able to choose the implementation, you can't use static methods. Static methods are looked up at compile time, so you can't call it based on a parameter (without reflection, but don't go there).

To call a static method, you would use SelectionSort.sort(...), but because you want to pass the implementation in you need to create an interface or abstract class which defines the sort method, then each implementation should implement that interface/extend the class.

 

I've built up a simple working example based on your code

(repl.it embeds are currently only available for admins, sorry)

Click the page button to show the files - I've added Sorter.java and modified SelectionSort.java to make it implement the Sorter interface.

 

5 hours ago, wasab said:

Well, you would pass an instance of a class into the static method to access it's members. The thing about static nested class is that an instance of an outter class does not need to exist just like if you use a static method, an instance of its class might not exist so there is no guranteed there is an instance of the class for you to invoke those none static methods or access member variables.

 

That is besides the point though. You don't need static everywhere and you seem to be abusing static quite a bit. I mean sure it is convenient because you don't need to deal with object instantiation and allow you to avoid OOP but if are determine to not use objects, then you really ought to be picking a programming language other than java. 

 

In your case, make sure that 

SortRunnable(SELECTION_SORT_TEXT, arr, SelectionSort.this);

is inside a nested class which is inside the SelectionSort class then there shouldn't be an error. You need to first instantiate selection sort class first. Instead of declaring nested class public, you should use a getter like you would for instance variables. 

 

E.g.

  Hide contents

Class SelectionSort{

     public SortRunnable getNewSortRunnable(){

          return new SortRunnable("super alogrithm", new int[10], this); // change these parameters to whatever you need. 

     }

 

    private class SortRunnable implements Runnable{

 

           public SortRunnable(String sortingAlgorithm, int[] arr, SelectionSort sorter){

               //Do what need with the parameters

           }

         

          @override

           public void run(){

              // Do what you need with the interface method.

          }

 

        

 

   }

 

}

Then you can first instantiate Selection Sort then call on getNewSortRunnable to get an instance of inner class then do what you need to do from here.

 

E.g.

  Hide contents

SelectionSort SSobj = new SelectionSort();

 

SortRunnable SRObj = SSobj.getNewSortRunnable();

 

Sorry if the code is sloppy. Im typing this on a phone. 

 

Edit, you don't need SelectionSort.this because as an inner class, SortRunnable already can access all the fields of the SelectionSort.

 

 

Thank you all for the help. Continues to impress me how helpful all of you are. I eventually figured it out as I had an error in my event listener the logic to determine what sorter to use happens in SortRunnable.java not Sorter.java. But the embedded repl.it is a really cool tool I just learned so I guess that's something lol