Cant solve "local variable needs to be final"

Question

Hi im trying to add calculations from my database depending on the user request but my float will not work unless its final, how can I get around this?

Code:

float v = (float) 0;
    StringBuilder upcoming = new StringBuilder("Upcoming\n\n");
    StringBuilder Results = new StringBuilder("Upcoming\n\n");
    switchExam.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            if(!isChecked)
            {
                for(FAssessment a : assessmentList) {
                    if(!a.getType().equals("Final"))
                    {
                        double d = CalculatePercentage(a.getTotal(),a.getAchieved(),Double.parseDouble(a.getWeight()));
                        v += (float) d;
                    }                        
                }
            }
            else
            {
                for(FAssessment a : assessmentList) {
                    double d = CalculatePercentage(a.getTotal(),a.getAchieved(),Double.parseDouble(a.getWeight()));
                    v += (float) d;
                }
            }
        }
    });

This is where I'm getting the error v += (float) d;

Variable 'v' is accessed from within inner class, needs to be final or effectively final

You are creating an anonymous class to be used as a `OnCheckedChangeListener`. That event con happen to the `switchExam` object in the future, well after the current function has finished (I mean the function where `float v` is scoped to), so where would the new value be stored? Since that variable will no longer be available, it makes no sense to store a reference to it. See https://stackoverflow.com/questions/4732544/why-are-only-final-variables-accessible-in-anonymous-class — frozenkoi, Oct 02 '18 at 23:48

score 2 · Answer 1 · answered Oct 02 '18 at 23:53

Maybe reverse who keeps what?

StringBuilder upcoming = new StringBuilder("Upcoming\n\n");
StringBuilder Results = new StringBuilder("Upcoming\n\n");

CompoundButton.OnCheckedChangeListener lister = new CompoundButton.OnCheckedChangeListener() {

    float v = 0.0;
    public float getV() { return v; }

    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if(!isChecked)
        {
            for(FAssessment a : assessmentList) {
                if(!a.getType().equals("Final"))
                {
                    double d = CalculatePercentage(a.getTotal(),a.getAchieved(),Double.parseDouble(a.getWeight()));
                    v += (float) d;
                }                        
            }
        }
        else
        {
            for(FAssessment a : assessmentList) {
                double d = CalculatePercentage(a.getTotal(),a.getAchieved(),Double.parseDouble(a.getWeight()));
                v += (float) d;
            }
        }
    }
};
switchExam.setOnCheckedChangeListener(lister);

then when the enclosing program needs to know what v is it can call

lister.getV();

NB: instead of casting 0 to a float, you might also be able to say something like:

float v = 0f;

[Another](https://stackoverflow.com/questions/14425826/variable-is-accessed-within-inner-class-needs-to-be-declared-final) way to put it: "Reason: if two methods see the same local variable, Java wants you to swear you will not change it - final, in Java speak. Together with the absence of by-reference parameters, this rule ensures that locals are only assigned in the method that they belong to..." — paulsm4, Oct 02 '18 at 23:58
Thank you very much for the input, I tried it but it didn't work — Erbez, Oct 03 '18 at 12:27

score 2 · Accepted Answer · answered Oct 03 '18 at 12:18

From what I understand, you want to use this variable v again later. If so, you can take the code you need and put it in a method. That way you can declare the variable in the listener, which would give it the final it is looking for.

Like this:

switchExam.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            StringBuilder upcoming = new StringBuilder("Upcoming\n\n");
            StringBuilder Results = new StringBuilder("Results\n\n");
            float v= 0;
            if(!isChecked)
            {

                for(FAssessment a : assessmentList) {
                    if(!a.getType().equals("Final"))
                    {
                        double d = CalculatePercentage(a.getTotal(),a.getAchieved(),Double.parseDouble(a.getWeight()));
                        v += (float) d;
                    }

                    upcoming.append(a.getDesc()+" "+a.getDate()+"\n");
                    Results.append(a.getDesc()+" "+format.format(((a.getAchieved()/a.getTotal())*100))+"%\n");
                }                    
                SetInit(v,upcoming,Results);
            }
            else
            {
                for(FAssessment a : assessmentList) {
                    double d = CalculatePercentage(a.getTotal(),a.getAchieved(),Double.parseDouble(a.getWeight()));
                    v += (float) d;
                    upcoming.append(a.getDesc()+" "+a.getDate()+"\n");
                    Results.append(a.getDesc()+" "+format.format(((a.getAchieved()/a.getTotal())*100))+"%\n");
                }
                SetInit(v,upcoming,Results);

            }
        }
    });
    switchExam.setChecked(true);

Then in your method, you would paste what you want to do with your variable v:

private void SetInit(float v, StringBuilder coming, StringBuilder results) {
    txtUpcoming.setText(coming);
    txtResults.setText(results);
    //And whatever you want to do with `v`
 }

Hope this helps. :)

Thank you very much, this helped! – Erbez Oct 03 '18 at 12:27 — Erbez, Oct 03 '18 at 12:27

Cant solve "local variable needs to be final"

2 Answers2