The final local variable cannot be assigned , cannot to the non-final variable

Question

I want to write the bmi calculation code in this program. When I specify variables "qad1" "vazn1" "bmi" "txtvazn" "txtqad" and "txtbmi" as final , I encountered this error: "The final local variable cannot be assigned" And when I did not specify them as final , I encountered this error: Cannot refer to the non-final local variable defined in an enclosing scope._ change modifier to final. I could not solve this problem with any trick.Please help me. The photo of the codes are uploaded here.Thank you.

public class Shakhes extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.shakhes);

         final EditText txtvazn=(EditText) findViewById(R.id.txtvazn);
         final EditText txtqad=(EditText) findViewById(R.id.txtqad);
         final TextView txtbmi=(TextView) findViewById(R.id.txtbmi);
         Button btnbmi=(Button) findViewById(R.id.btnbmi);
         final int qad1;
         final int vazn1;
         final float bmi;

        btnbmi.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View arg0) {
                qad1=Integer.parseInt(txtqad.getText().toString());
                qad1=qad1/100;
                vazn1=Integer.parseInt(txtvazn.getText().toString());
                bmi=vazn1/(qad1*qad1);
                txtbmi.setText(""+bmi);
            }
        });
    }
}

Answer 1

You can define variables inside onClickListener if use use them only inside listener:

( UPDATE as @DEADMC noted, final is not required more in that case)

 btnbmi.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            int qad1;
            int vazn1;
            float bmi;

            // all other code

On the other hand, if scope of variable is more than listener, convert it to single-item array:

final int[] qad1 = new int[] {0};

 btnbmi.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
             qad1[0] = ...
       }
 }

Answer 2

Please take some read of immutability benefits in the first place (guess link http://okyasoft.blogspot.com/2014/05/6-benefits-of-programming-with_5146.html )

For your example, please try to make all the variable references you are trying to use under OnClickListener - as class fields (instead of method variables).

Defining, for example, txtbmi as class member ( private TextView txtbmi; ) will automatically make it accessible to all the inner classes of your Shakhes activity.