Android fechData using Retrofit Application's screenshot at first comment

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:id="@+id/text_view_result"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="#000000"

            />
    </android.support.v4.widget.NestedScrollView>
</LinearLayout>

Android fechData using Retrofit

 json url (https://jsonplaceholder.typicode.com/posts)
 from website( https://jsonplaceholder.typicode.com/ )

AndroidMainfest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.mostafa.jsonretrofit">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "com.example.mostafa.jsonretrofit"
        minSdkVersion 19
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:27.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    // Retofit
    //implementation 'com.squareup.retrofit2:retrofit:2.4.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.4.0'
}

JsonplaceholderApi.java

package com.example.mostafa.jsonretrofit;

import java.util.List;

import retrofit2.Call;
import retrofit2.http.GET;

public interface JsonplaceHolderApi   {


    // create one method that return Call Object
    /**
     *  this is what we want to get back from this car
     *  a list of posts which is a json array of posts
     *  json objects that we saw
     */
    @GET("posts") // posts is relative URL  from here (https://jsonplaceholder.typicode.com/posts)
    Call<List<Post>>getPosts();
}

MainActivity.java

package com.example.mostafa.jsonretrofit;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import java.util.List;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class MainActivity extends AppCompatActivity {
    private TextView textviewResult;

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

        textviewResult = findViewById(R.id.text_view_result);


        // below we will execute our actual get request
        // this retrofit instance we can now create our json placeholder api
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://jsonplaceholder.typicode.com/")
                // this is how we define that we want to use json to a pass the response
                .addConverterFactory(GsonConverterFactory.create())
                .build();

         JsonplaceHolderApi jsonplaceHolderApi = retrofit.create(JsonplaceHolderApi.class);

         // to executr our network request


        Call<List<Post>> call = jsonplaceHolderApi.getPosts();
        call.enqueue(new Callback<List<Post>>() {
            /**
             * when we get a response back from the server
             * but doesn't mean that our request was successful
             * because the server code for EX: responds with a 404
             * @param call
             * @param response
             */
            @Override
            public void onResponse(Call<List<Post>> call, Response<List<Post>> response) {

                // check respons is successful
                if(!response.isSuccessful()){
                    textviewResult.setText("Code: "+ response.code());
                    return;

                }

                // here actuly Data that we want from web serves
                List<Post> posts = response.body();

                // here we will display this data in textview

                for(Post post : posts){

                    String content = "";
                    content+= "ID: "+ post.getId()+"\n";
                    content+= "User ID: "+ post.getUserId()+"\n";
                    content+= "Title: "+ post.getTitle()+"\n";
                    content+= "Body: "+ post.getText()+"\n\n";

                    textviewResult.append(content);
                }
            }

            /**
             *  Failure means that something went wrong in the communication with the
             *  server pr processing the response
             *
             * @param call
             * @param t
             */
            @Override
            public void onFailure(Call<List<Post>> call, Throwable t) {

                textviewResult.setText(t.getMessage());


            }
        });
    }
}

Post.java

package com.example.mostafa.jsonretrofit;

import com.google.gson.annotations.SerializedName;

public class Post {

    // here  name of json value
    private  int userId ;
    private  int id;
    private  String title;

    @SerializedName("body")
    private String text;

    // Getter methods
    public int getUserId() {
        return userId;
    }

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getText() {
        return text;
    }
}