Api Implementation in java

• Create Interface class

@GET("posts")
    Call<ArrayList<ApiModelResponse>> getresponse();
}

• create retrofit class

package com.example.testapiimplementation.Network;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.concurrent.TimeUnit;

import okhttp3.OkHttpClient;
import okhttp3.logging.HttpLoggingInterceptor;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class RetrofitClass {

    private static Retrofit retrofit;
    private static final String BASEURL="https://jsonplaceholder.typicode.com/";


    public static Retrofit getRetrofit(){
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient apiClient = new OkHttpClient.Builder()
                .addInterceptor(interceptor)
                .readTimeout(8000, TimeUnit.SECONDS)
                .writeTimeout(8000, TimeUnit.SECONDS)
                .connectTimeout(8000
                        , TimeUnit.SECONDS)
                .retryOnConnectionFailure(false)
                .build();
        Gson gson = new GsonBuilder()
                .setLenient()
                .create();


        retrofit = new Retrofit.Builder()
                .baseUrl(BASEURL)
                .addConverterFactory(GsonConverterFactory.create(gson))
                .client(apiClient)
                .build();

        return retrofit;
    }
}

• if not added in gradle add these lines

implementation 'com.squareup.retrofit2:retrofit:2.9.0'
implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
implementation("com.squareup.okhttp3:logging-interceptor:4.9.1")
implementation 'com.google.code.gson:gson:2.9.0'

• if you are adding for recycler view add these 

package com.example.testapiimplementation.Adapter;

import android.content.Context;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

import com.example.testapiimplementation.Model.ApiModelResponse;
import com.example.testapiimplementation.R;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Shweta.Chauhan on 13/07/16.
 */

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.MyViewHolder>{

    private Context context;
    private ArrayList<ApiModelResponse> dataList;

    public RecyclerAdapter(Context context,   ArrayList<ApiModelResponse> dataList) {
        this.context = context;
        this.dataList = dataList;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.layout_row,parent,false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.txt1.setText(dataList.get(position).getTitle());
        holder.txt2.setText(dataList.get(position).getUserId().toString());
        holder.txt2.setText(dataList.get(position).getBody());

    }

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

    public class MyViewHolder extends RecyclerView.ViewHolder{

        public TextView txt1,txt2,txt3;

        public MyViewHolder(View itemView) {
            super(itemView);
           txt1=itemView.findViewById(R.id.txtbody);txt2=itemView.findViewById(R.id.txttitle);
           txt3=itemView.findViewById(R.id.txtid);

        }
    }
}

• add this in your activity file

package com.example.testapiimplementation;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;

import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;

import com.example.testapiimplementation.Adapter.RecyclerAdapter;
import com.example.testapiimplementation.Interface.ApiInterface;
import com.example.testapiimplementation.Model.ApiModelResponse;
import com.example.testapiimplementation.Network.RetrofitClass;
import com.example.testapiimplementation.databinding.ActivityMainBinding;

import java.util.ArrayList;
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 {

ActivityMainBinding mainBinding;
ApiInterface apiInterface;
    ArrayList<ApiModelResponse>  apiModelResponse;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mainBinding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(mainBinding.getRoot());

        apiModelResponse = new ArrayList<>();
        apiInterface=RetrofitClass.getRetrofit().create(ApiInterface.class);
        apiInterface.getresponse().enqueue(new Callback<ArrayList<ApiModelResponse>>() {
            @Override
            public void onResponse(Call<ArrayList<ApiModelResponse>> call, Response<ArrayList<ApiModelResponse>> response) {
                if(response.body()!=null){
                    apiModelResponse=response.body();
                    mainBinding.rectony.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
                    RecyclerAdapter recyclerAdapter1=new RecyclerAdapter(MainActivity.this,apiModelResponse);
                    mainBinding.rectony.setAdapter(recyclerAdapter1);
                    Toast.makeText(MainActivity.this, "ok", Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onFailure(Call<ArrayList<ApiModelResponse>> call, Throwable t) {
                Toast.makeText(MainActivity.this, "not ok", Toast.LENGTH_SHORT).show();
            }
        });

    }
}