title: Multiple questions related to Flutter basic
body: <p>I am coming from React and trying to understand Flutter. There are some differences between dart vs JS and React vs Flutter. However, it seems a bit similar to each other. However, there is some confusion toward Flutter.</p>
  <ol>
  <li><code>void</code></li>
  </ol>
  <p>It does not return the value. Therefore, it is used to <code>void main()</code>. Does it mean like the function 'main()' will be executed and I will never be able to reuse <code>void main()</code>?</p>
  <ol start="2">
  <li><code>&lt;&gt;</code></li>
  </ol>
  <p>In the code, I have here</p>
  <pre><code>class LoginScreen extends StatefulWidget {
    createState() {
      return new LoginScreenState();
    }
  }
  
  class LoginScreenState extends State&lt;LoginScreen&gt; {
    Widget build(context) {
      return Container(
          margin: EdgeInsets.all(20.0),
          child: Column(
            children: [
              emailField(),
              // passwordField(),
              // submitButton(),
            ],
          ));
    }
  }
  </code></pre>
  <p>I can see that <code>State&lt;LoginScreen&gt;</code> is related to <code>class LoginScreen</code>. It is an extension of the <code>LoginScreen</code> State?</p>
  <pre><code>Future&lt;int&gt; successor = future.then((int value) {
    
    },
   
  </code></pre>
  <p>However, in here Future &lt;----- I do not understand why it has to state 'int' in this code. What is the proper use of <code>&lt;&gt;</code>?</p>
  <ol start="3">
  <li>Stateful vs Stateless</li>
  </ol>
  <p>Can I just use the <code>Stateful</code> all the time even if I do not have any state like React? Where there is no difference?</p>