Retrofit Library + RecyclerView

Dependencies

implementation 'com.squareup.retrofit2:retrofit:2.9.0'
implementation 'com.squareup.retrofit2:converter-gson:2.9.0'

RetrofirActivity.java

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    android:layout_marginHorizontal="20dp"
    app:layout_constraintTop_toBottomOf="@+id/toolbar" />

RetrofitApi.java

public interface RetrofitApi {

    @GET("demo.json")
    Call<List<UserModel>> userlist();

}

RetrofitLibActivity.java

public class RetrofitLibActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    List<UserModel> userlist;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_retrofit_lib);

        recyclerView = findViewById(R.id.recyclerview);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        Retrofit retrofit = new Retrofit.Builder().baseUrl("https://nilsn1.github.io/nilscreation/")
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        RetrofitApi retrofitApi = retrofit.create(RetrofitApi.class);

        Call<List<UserModel>> call = retrofitApi.userlist();

        call.enqueue(new Callback<List<UserModel>>() {
            @Override
            public void onResponse(Call<List<UserModel>> call, Response<List<UserModel>> response) {

                userlist = response.body();
                UserAdapter adapter = new UserAdapter(RetrofitLibActivity.this, userlist);
                recyclerView.setAdapter(adapter);

            }

            @Override
            public void onFailure(Call<List<UserModel>> call, Throwable t) {
                Toast.makeText(RetrofitLibActivity.this, "" + t.getMessage(), Toast.LENGTH_SHORT).show();

            }
        });

    }
}

UserAdapter.java

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {

    Context context;
    List<UserModel> userlist;

    public UserAdapter(Context context, List<UserModel> userlist) {
        this.context = context;
        this.userlist = userlist;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(context).inflate(R.layout.user_item, parent, false);
        return new ViewHolder(view);

    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        UserModel user = userlist.get(position);
        holder.userId.setText("" + user.getUserid());
        holder.userName.setText(user.getUsername());
        holder.country.setText(user.getCountry());

    }

    @Override
    public int getItemCount() {
        return userlist.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        TextView userId, userName, country;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);

            userId = itemView.findViewById(R.id.userId);
            userName = itemView.findViewById(R.id.userName);
            country = itemView.findViewById(R.id.country);
        }
    }
}

user_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dp"
    android:background="@drawable/custominput"
    android:orientation="vertical">

    <TextView
        android:id="@+id/userId"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fontFamily="@font/nunito_bold"
        android:text="Userid"
        android:textColor="@color/text_color"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/userName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:fontFamily="@font/nunito_bold"
        android:text="Username"
        android:textColor="@color/text_color"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/country"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:fontFamily="@font/nunito_bold"
        android:text="Country"
        android:textColor="@color/text_color"
        android:textSize="20sp" />

</LinearLayout>

UserModel.java

public class UserModel {

    int userid;
    String username;
    String country;

    public UserModel(int userid, String username, String country) {
        this.userid = userid;
        this.username = username;
        this.country = country;
    }

    public int getUserid() {
        return userid;
    }

    public void setUserid(int userid) {
        this.userid = userid;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }
}