Can't assign local variable because it is defined in outside

Question

i'm writing a static method and i'm experiencing problems with accessing variable from inner method. I'm getting the following error in Eclipse:

The final local variable ret cannot be assigned, since it is defined in an enclosing type

Here is my code:

public static boolean noInternetAlertDialog(Context ctx) {
    final boolean ret;

    AlertDialog.Builder builder;
    builder = new AlertDialog.Builder(ctx);
    builder.setCancelable(false);
    builder.setTitle("Error");
    builder.setMessage("Connection error");

    builder.setPositiveButton("Retry", new DialogInterface.OnClickListener(){
        @Override
        public void onClick(DialogInterface dialog, int which)
        {
            dialog.dismiss();
            ret = false;
        }
    });

    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.dismiss();
            ret = false;
        }
    });         
    AlertDialog dialog = builder.create();
    dialog.show();

   if (ret)
       return true;
   else
       return false;
}

try it with just the declaration alone: (i.e. final boolean ret=false;) and don't set it in your inner methods — Martin, Nov 18 '14 at 18:47
I get this error at `ret = false;`, not at `final boolean ret;` — smartmouse, Nov 18 '14 at 18:50

score 1 · Answer 1 · answered Nov 18 '14 at 18:48

The point is that method-local variables from the enclosing type are actually copied to instances of anonymous classes (this is because of activation frame issues, but I won't go further into detail as this is not really relevant to the question), which is why they need to be final, because the variable in the nested type instance is not the same anymore.

So, here is the first example:

void foo() {
    int a = 3;
    new Runnable() {
        @Override
        public void run() {
            a += 3;
        }
    };
}

This does not compile, because you cannot reference a non-final variable in an anonymous class' method. When you add a final modifier to the declaration of a, the value of a would be copied into the created instance of the anonymous class you have defined. However, you will not be allowed to change the value of a, because the changes would not be visible to the method where a was declared.

However, anonymous classes are not static, that is, they have a reference to the enclosing instance (unless the method where they are declared is static) which you can use to modify variables of the enclosing instance:

int a = 3;

    void foo() {
        new Runnable() {
            @Override
            public void run() {
                a += 3;
            }
        };
    }

This example does compile and it would increase a by 3 every time the run() method of the anonymous class' instance is called. (In this example it is never called, but it is just an example.)

So, to summarize, you need to convert the variable seatno from a method-local variable to an instance variable of the enclosing type. Or, if it is yet, you need to remove the final modifier as final variables can only be assigned once.

Update: In Java 8, the concept of effectively final variables is introduced (see Java Language Specification). However, in the first example of this post, the variable a is assigned multiple times, which prevents it from being effectively final. This means that this example still does not compile with Java 8. (The compile error is "Local variable a defined in an enclosing scope must be final or effectively final")

I do add `boolean ret = false;` at the begin of the class (before the method) but i get the following error: `Cannot make a static reference to the non-static field ret` — smartmouse, Nov 18 '14 at 18:54

score 0 · Answer 2 · edited May 23 '17 at 12:06

0

You are mixing synchronous and asynchronous code. Your boolean method will execute all of the code and return before you show your dialog. Instead you either need to provide a callback or call a method inside of the click listeners. Something like this...

public static void showNoInternetDialog(Context context) {
//setup here.
    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {

            userTappedCancel();
        }
    });  

}

private static void userTappedCancel()
{
   //Do whatever you want here
}

You'll need to do the same for the setPositiveButton() as well. See this questions for a different example.

edited May 23 '17 at 12:06

Community

1
1

answered Nov 18 '14 at 18:48

kevskree

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I can't use this solution, i just need to validate "ret" variable. – smartmouse Nov 18 '14 at 18:57
You are architecting your code in an unusable way. The method will execute all of the code and return false before the user will be able to tap a button in the dialog. The only way to get a value when showing an *asynchronous* dialog is with callbacks or calling methods inside the click listeners. The [Android docs](http://developer.android.com/guide/topics/ui/dialogs.html) do a very good job at explaining how to show dialogs and respond to user input. – kevskree Nov 18 '14 at 19:02

score 0 · Answer 3 · answered Nov 19 '14 at 19:29

public static boolean noInternetAlertDialog(Context ctx) {
final boolean ret = false;   //<+======== this

AlertDialog.Builder builder;
builder = new AlertDialog.Builder(ctx);
builder.setCancelable(false);
builder.setTitle("Error");
builder.setMessage("Connection error");

builder.setPositiveButton("Retry", new DialogInterface.OnClickListener(){
    @Override
    public void onClick(DialogInterface dialog, int which)
    {
        dialog.dismiss();
        // =====>    you don't need this - ret = false;
    }
});

builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        dialog.dismiss();
        // =====>    you don't need this - ret = false;
    }
});         
AlertDialog dialog = builder.create();
dialog.show();

if (!ret) return true; else return false; }

since you only set it to false, you don't need to change it.

Can't assign local variable because it is defined in outside

3 Answers3