title: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
body: <p>My app is crashing even though I instantiated my buttons to my activity. What am I doing wrong? Here is my xml and java code. Please help me I really need help right now. I don't know what to do. Here is my error stack:</p>
  
  <pre><code>Process: com.example.dith.finalproject3, PID: 9301
      java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dith.finalproject3/com.example.dith.finalproject3.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
          at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
          at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
          at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
          at android.os.Handler.dispatchMessage(Handler.java:106)
          at android.os.Looper.loop(Looper.java:193)
          at android.app.ActivityThread.main(ActivityThread.java:6669)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
          at com.example.dith.finalproject3.MainActivity.expansions(MainActivity.java:193)
          at com.example.dith.finalproject3.MainActivity.onCreate(MainActivity.java:63)
          at android.app.Activity.performCreate(Activity.java:7136)
          at android.app.Activity.performCreate(Activity.java:7127)
          at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
  </code></pre>
  
  <p>Here is my java code:</p>
  
  <pre><code>public void expansions()
  {
          btnCalendar = (ImageButton) findViewById(R.id.btnCalendar);
          btnCalendarHide = (Button) findViewById(R.id.btnCalendarHide);
          expCalendar = (View) findViewById(R.id.expCalendar);
          expCalendar.setVisibility(View.INVISIBLE);
  }
  </code></pre>
  
  <p>Written below is my XML file:</p>
  
  <pre><code>&lt;LinearLayout
                          android:id="@+id/expCalendar"
                          android:layout_width="match_parent"
                          android:layout_height="wrap_content"
                          android:orientation="vertical"&gt;
  
                          &lt;TextView
                              android:id="@+id/txtCalendar"
                              android:layout_width="wrap_content"
                              android:layout_height="wrap_content"
                              android:padding="@dimen/spacing_large"
                              android:text="Calendar Placeholder" /&gt;
  
                          &lt;View
                              android:layout_width="match_parent"
                              android:layout_height="1dp"
                              android:background="@color/grey_10" /&gt;
  
                          &lt;LinearLayout
                              android:layout_width="match_parent"
                              android:layout_height="wrap_content"
                              android:gravity="end"
                              android:orientation="horizontal"&gt;
  
                              &lt;Button
                                  android:id="@+id/btnCalendarHide"
                                  style="@style/Widget.AppCompat.Button.Borderless"
                                  android:layout_width="wrap_content"
                                  android:layout_height="wrap_content"
                                  android:gravity="center"
                                  android:text="HIDE" /&gt;
  
                          &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>Thank you very much enjoy your day!</p>