title: how to solve the incompatible when using IF ELSE statement in Android studio?
body: <p>when I created the the (EditText) fields a , b and c ,I let it's type as a number (android:inputType="number"), then when I tried to write the following code I got a hint told me that there is an incompatible .</p>
  
  <pre><code>    button.setOnClickListener(new View.OnClickListener() {
                            @Override
              public void onClick(View v) {
  
               if(!"".equals(a.getText())
               &amp;&amp;!"".equals(b.getText())
               &amp;&amp;!"".equals(c.getText())) {
  
                                double a1 = Double.parseDouble(a.getText().toString());
                                double b1 = Double.parseDouble(b.getText().toString());
                                double c1 = Double.parseDouble(c.getText().toString());
  
                                Double r = b1 * c1 / a1;
                                result.setText(r.toString());
                            }
  
                            else{
                                    Toast.makeText(MainActivity.this,"Not A Real Value",Toast.LENGTH_SHORT).show();
                                }
  
                            }
          });
  </code></pre>