Variable is accessed within inner class Needs to be declared final

Question

I m getting a compilation error inside of my onClick  Here s the code  public class fieldsActivity extends Activity    Button addSiteButton  Button cancelButton  Button signInButton           Called when the activity is first created       Override public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState          to create a custom title bar for activity window     requestWindowFeature Window FEATURE CUSTOM TITLE        setContentView R layout fields          use custom layout title bar     getWindow   setFeatureInt Window FEATURE CUSTOM TITLE  R layout topbar        Pager adapter   new Pager        ViewPager mPager    ViewPager  findViewById R id fieldspager       mPager setAdapter adapter       mPager setCurrentItem 1          addSiteButton    Button  findViewById R id addSiteButton       addSiteButton setOnClickListener new View OnClickListener               Override         public void onClick View v               mPager setCurrentItem 2  true     Compilation error happens here                            cancelButton    Button  findViewById R id cancel button       signInButton    Button  findViewById R id sign in button

User · Answer

As  Veger said  you can make it final so that the variable can be used in the inner class   final ViewPager pager    ViewPager  findViewById R id fieldspager     I called it pager rather than mPager because you are using it as a local variable in the onCreate method  The m prefix is cusomarily reserved for class member variables  i e  variables that are declared at the beginning of the class and are available to all class methods    If you actually do need a class member variable  it doesn t work to make it final because you can t use findViewById to set its value until onCreate  The solution is to not use an anonymous inner class  This way the mPager variable doesn t need to be declared final and can be used throughout the class   public class MainActivity extends AppCompatActivity        private ViewPager mPager      private Button mButton        Override     public void onCreate Bundle savedInstanceState                            mPager    ViewPager  findViewById R id fieldspager                            mButton setOnClickListener myButtonClickHandler               View OnClickListener myButtonClickHandler   new View OnClickListener              Override         public void onClick View view                mPager setCurrentItem 2  true

User · Answer

You can declare the variable final  or make it an instance  or global  variable  If you declare it final  you won t be able to change it later   Any variable defined in a method and accessed by an anonymous inner class must be final  Otherwise  you could use that variable in the inner class  unaware that if the variable changes in the inner class  and then it is used later in the enclosing scope  the changes made in the inner class did not persist in the enclosing scope  Basically  what happens in the inner class stays in the inner class   I wrote a more in-depth explanation here  It also explains why instance and global variables do not need to be declared final

User · Answer

The error says it all  change   ViewPager mPager    ViewPager  findViewById R id fieldspager     to  final ViewPager mPager    ViewPager  findViewById R id fieldspager

User · Answer

Here s a funny answer   You can declare a final one-element array and change the elements of the array all you want apparently   I m sure it breaks the very reason why this compiler rule was implemented in the first place but it s handy when you re in a time-bind as I was today   I actually can t claim credit for this one   It was IntelliJ s recommendation   Feels a bit hacky   But doesn t seem as bad as a global variable so I thought it worth mentioning here  It s just one solution to the problem   Not necessarily the best one   final int   tapCount    0    addSiteButton setOnClickListener new View OnClickListener           Override     public void onClick View v           tapCount 0

User · Answer

public class ConfigureActivity extends Activity            EditText etOne          EditText etTwo           Override         protected void onCreate Bundle savedInstanceState                super onCreate savedInstanceState               setContentView R layout activity configure                Button btnConfigure   findViewById R id btnConfigure1                  btnConfigure setOnClickListener new View OnClickListener                              Override                         public void onClick View v                                configure                                                                 public  void configure                String one   etOne getText   toString                String two   etTwo getText   toString

User · Answer

If you don t want to make it final  you can always just make it a global variable

[java] Variable is accessed within inner class. Needs to be declared final

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