Retrofit Boilerplate

DummyApi.java

public interface DummyApi {

    @GET("posts")
    Call<DemoPost> fetchDummyPosts();
  
    @GET("comments")
    Call<DemoComment> fetchDummyComments();

}

DummyApiBuilder.java

public class DummyApiBuilder {

    private static final String BASE_URL = "https://jsonplaceholder.typicode.com/";

    private static Retrofit retrofit = null;

    public static Retrofit getClient() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
}

DummyComment.java

public class DummyComment {

@SerializedName("postId")
@Expose
private Integer postId;
@SerializedName("id")
@Expose
private Integer id;
@SerializedName("name")
@Expose
private String name;
@SerializedName("email")
@Expose
private String email;
@SerializedName("body")
@Expose
private String body;

public Integer getPostId() {
return postId;
}

public void setPostId(Integer postId) {
this.postId = postId;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

public String getBody() {
return body;
}

public void setBody(String body) {
this.body = body;
}

}

DummyPost.java

public class DummyPost {

@SerializedName("userId")
@Expose
private Integer userId;
@SerializedName("id")
@Expose
private Integer id;
@SerializedName("title")
@Expose
private String title;
@SerializedName("body")
@Expose
private String body;

public Integer getUserId() {
return userId;
}

public void setUserId(Integer userId) {
this.userId = userId;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getTitle() {
return title;
}

public void setTitle(String title) {
this.title = title;
}

public String getBody() {
return body;
}

public void setBody(String body) {
this.body = body;
}

}

Library

Retrofit : implementation 'com.squareup.retrofit2:retrofit:2.4.0'
Gson :   implementation 'com.google.code.gson:gson:2.4.0'

MainActivity.java

DummyApiBuilder.getClient().create(DummyApi.class)
                .fetchDummyPosts()
                .enqueue(new Callback<DummyPost>() {
                    @Override
                    public void onResponse(@NonNull Call<DummyPost> call, @NonNull Response<DummyPost> response) {
                        
                    }

                    @Override
                    public void onFailure(Call<DummyPost> call, Throwable t) {
                        
                    }
});