stage1.java

class SomethingActivity extends AppCompatActivity {
  @Override
  void onCreate() {
    super.onCreate();
    setContentView(R.layout.activity_something);
  }
  
  @Override
  void onResume() {
    retrofitService.someApiEndpoint().enqueue(this);
  }
  
  @Override
  void onResponse(Call<Something> call, Response<Pojo> response) {
    //TODO handle your api call here, set some text field, hide some other field
  }
  
  @Override
  void onFailure(Call<Something> call, Throwable t) {
    //TODO show some error message, or a toast, or throw it to error logging tool
  }
}