title: Java: cannot find symbol class
body: <p>I am writing a program, which gets two values from two text fields and calculates their result.</p>
  
  <p>The problem is that Java Editor shows me the following errors:</p>
  
  <pre><code>cannot find symbol class EditText
  cannot find symbol class Button
  cannot find symbol class string
  cannot find symbol class variable integer
  cannot find symbol class integer
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity
  {
      EditText firstNumber;
      EditText secondNumber;
      Button btnAdd;
      TextView total;
  
  
      @Override
      protected void onCreate(Bundle savedInstanceState)
      {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          firstNumber = (EditText)findViewById(R.id.firstNumber);
          secondNumber = (EditText)findViewById(R.id.secondNumber);
          btnAdd = (Button)findViewById(R.id.btnAdd);
          total = (TextView)findViewById(R.id.total);
    }
  
      public void btnAdd_Click(View view)
      {
          string getfirstNumber = firstNumber.getText().toString();
          string getsecondNumber = secondNumber.getText().toString();
  integer totalResult = integer.parseInt(getfirstNumber) + integer.parseInt(getsecondNumber);
  total.setText("Total = " + integer.toString(totalResult));
  
      }
  }
  </code></pre>