Building the user interface

Put simply, Android user interfaces are based on Activities, which use layout files to describe the structure of the user interface. There's more to it, of course, but this simple definition should be sufficient for our work on Sunago. Let's start, then, by looking at our Activity, MainActivity, which is as follows:

    public class MainActivity extends AppCompatActivity { 
      @Override 
      protected void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.activity_main); 
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
        setSupportActionBar(toolbar); 
 
        FloatingActionButton fab =
            (FloatingActionButton) findViewById(R.id.fab); 
        fab.setOnClickListener(new View.OnClickListener() { 
            @Override 
            public void onClick(View view) { 
                Snackbar.make(view,
                        "Replace with your own action",
   ...