title: error: cannot find symbol variable MyClass in android
body: <p>I have a simple project. In this project I created a <code>java library</code> as follows:</p>
  
  <pre><code>package com.example;
  import java.lang.Integer;
  public class Sum {
  public static Integer counter(int number_1, int number_2){
      return number_1 + number_2;
  }
  }
  </code></pre>
  
  <p>And in <code>MainActivit</code> class I have the following code:</p>
  
  <pre><code>package com.example.tec.myapplication;
  import com.example.Sum;
  import android.app.Activity;
  import android.os.Bundle;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.widget.TextView;
  
  public class MainActivity extends Activity {
      TextView textView;
      int number_1 = 100;
      int number_2 = 100;
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          textView = (TextView) findViewById(R.id.textView);
      Integer integer =  Sum.counter(number_1, number_2);
      textView.setText(integer.toString());
      }}
  </code></pre>
  
  <p>In appearance, My codes have no grammatical problem and I do not get even a warning from the android studio. But when I click on the <code>run</code> option I get the following errors:</p>
  
  <pre><code>C:\Users\tec\AndroidStudioProjects\MyApplication\app\src\main\java\com\example\tec\myapplication\MainActivity.java
  
  Error:(2, 19) error: cannot find symbol class MyClass
  Error:(17, 24) error: cannot find symbol variable MyClass
  Error:Execution failed for task ':app:compileDebugJavaWithJavac'.
  &gt; Compilation failed; see the compiler error output for details.
  </code></pre>
  
  <p>In the above code, seems I have three errors.</p>