title: JAVA - Variable is always null
body: <p>I've made this code where the variable <code>DEVICE</code> will change if a file exist or not. So i have made this code but the variable <code>DEVICE</code> is always null</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity{
  
      String DEVICE;
  
   @Override
      protected void onCreate(Bundle savedInstanceState) {
  
          apply = (Button) findViewById(R.id.apply);
          apply.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                      checktypezip(DEVICE);
                      while (DEVICE == null){
                          Log.v("Check","Check non completo");
                      }
              }
          });
  
      }
  
      public void checktypezip(String string){
          String percorso = Environment.getExternalStorageDirectory().getPath()+"/BAC/.unzipfile/";
  
          File normalzip = new File (percorso+"desc.txt");
          File flashzip = new File (percorso+"/system/media/bootanimation.zip");
          File samsung = new File (percorso+"/bootsamsung.qmg");
          File flashsamsung = new File (percorso+"/system/media/bootsamsung.qmg");
          String disp;
  
          disp=string;
          if (normalzip.exists()){
              disp = "Normal";
              string=disp;
          }
          else if (flashzip.exists()){
              disp = "Flashnormal";
              string=disp;
          }
          else if (samsung.exists()){
              disp = "Samsung";
              string=disp;
          }
          else if (flashsamsung.exists()){
              disp = "Samsungflash";
              string=disp;
          }
          else
          {
              disp = "Unknown";
              string=disp;
          }
  
      }
  
  }
  </code></pre>