title: App crashes repeatedly due to empty EditText
body: <p>I have created a simple app to calculate the discount. it works fine when the values are provided, but keeps on crashing when calculation is done with empty text fields. thanks in advance..!!</p>
  
  <pre><code>public class Firstctivity extends AppCompatActivity {
     Button find;
     EditText ed1,ed2;
     TextView tv1;
     @Override
     protected void onCreate(Bundle savedInstanceState)
     {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_firstctivity);
      find=(Button)findViewById(R.id.button);
      tv1=(TextView)findViewById(R.id.text39);
      ed1=(EditText)findViewById(R.id.sai);
      ed2=(EditText)findViewById(R.id.editText);
  
  
      find.setOnClickListener(new View.OnClickListener()
      {
          public void onClick(View v)
          {
  
              final double a =Double.parseDouble(String.valueOf(ed1.getText()));
              final double b =Double.parseDouble(String.valueOf(ed2.getText()));
              double results;
              double c;
             try {
                 c = a * b;
                 results = c / 100;
                 String total2 = String.valueOf(results);
                 // String total2="fuck u";
                 tv1.setText("You have recieved Rs" + total2 + "/- concession.");
                 tv1.setBackgroundColor(Color.parseColor("#4169E1"));
                 }
            catch (NumberFormatException ex)
  
             {
  
             }
  
  
          }
  
      });
  
  
  }
  </code></pre>
  
  <p>}</p>