In the early days of
Android development, most nontrivial apps have more than one screen, and the UI was partitioned across multiple Activities. That meant you needed the skill to navigate from one Activity to another and back. So, during those days, you might have written something that looks like the code in Listing
10-1.
class FirstActivity extends AppCompatActivity
implements View.OnClickListener {
public void onClick(View v) {
Intent intent ...