title: Java Error: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
body: <p>I get the error "Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference" when I want the start my app.</p>
  
  <p>The error output</p>
  
  <pre><code>02-09 19:39:20.364 18846-18846/com.michael1011.tweetcomposer E/AndroidRuntime: FATAL EXCEPTION: main
     Process: com.michael1011.tweetcomposer, PID: 18846
     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.michael1011.tweetcomposer/com.michael1011.tweetcomposer.login}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2450)
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2520)
         at android.app.ActivityThread.-wrap11(ActivityThread.java)
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363)
         at android.os.Handler.dispatchMessage(Handler.java:102)
         at android.os.Looper.loop(Looper.java:148)
         at android.app.ActivityThread.main(ActivityThread.java:5466)
         at java.lang.reflect.Method.invoke(Native Method)
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
         at android.support.design.widget.Snackbar.setText(Snackbar.java:334)
         at android.support.design.widget.Snackbar.make(Snackbar.java:210)
         at com.michael1011.tweetcomposer.login.onCreate(login.java:43)
         at android.app.Activity.performCreate(Activity.java:6251)
         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2403)
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2520) 
         at android.app.ActivityThread.-wrap11(ActivityThread.java) 
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363) 
         at android.os.Handler.dispatchMessage(Handler.java:102) 
         at android.os.Looper.loop(Looper.java:148) 
         at android.app.ActivityThread.main(ActivityThread.java:5466) 
         at java.lang.reflect.Method.invoke(Native Method) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
  </code></pre>
  
  <p>mainActivity.java</p>
  
  <pre><code>public class login extends AppCompatActivity {
  
  public boolean isOnline() {
      NetworkInfo netInfo = ((ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo();
      if (netInfo == null || !netInfo.isConnectedOrConnecting()) {
          return false;
      }
      return true;
  }
  
  Intent sb_login = null;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_login);
  
      Toolbar login_toolbar = (Toolbar) findViewById(R.id.toolbar_login);
      setSupportActionBar(login_toolbar);
  
      RelativeLayout login_sb_layout = (RelativeLayout)findViewById(R.id.login_layout);
  
      Snackbar sb_login = Snackbar
              .make(login_sb_layout, "@string/no_internet_connection", Snackbar.LENGTH_INDEFINITE)
              .setAction("RETRY", new View.OnClickListener() {
                  @Override
                  public void onClick(View v) {
                      recreate();
                  }
              });
  
      sb_login.setActionTextColor(Color.parseColor("#55acee"));
  
      View sb_login_view = sb_login.getView();
      TextView sb_login_textView = (TextView)sb_login_view.findViewById(android.support.design.R.id.snackbar_text);
      sb_login_textView.setTextColor(Color.parseColor("#ffffff"));
  
      if(!isOnline()) {
          sb_login.show();
      }
  }
  
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      getMenuInflater().inflate(R.menu.menu_login, menu);
      return true;
  }
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
  
      int id = item.getItemId();
  
      if (id == R.id.action_settings) {
  
          startActivity(new Intent(this, settings.class));
          return true;
      }
  
      return super.onOptionsItemSelected(item);
  }}
  </code></pre>
  
  <p>Please help.</p>