Response.Listener<String> responseListener = new Response.Listener<String>(){}

import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONException;
import org.json.JSONObject;

public class LoginActivity extends AppCompatActivity {

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

    final EditText etUsername = (EditText) findViewById(R.id.etUsername);
    final EditText etPassword = (EditText) findViewById(R.id.etPassword);
    final Button bLogin = (Button) findViewById(R.id.bLogin);
    final TextView tvRegister = (TextView) findViewById(R.id.tvRegister);


    bLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {


            final String username = etUsername.getText().toString();
            final String password = etPassword.getText().toString();



               Response.Listener<String> responseListener = new Response.Listener<String>() {
                   @Override
                   public void onResponse(String response) {


                       try {
                           JSONObject jsonResponse = new JSONObject(response);
                           boolean success = jsonResponse.getBoolean("success");

                           if (success) {

                               Intent intent = new Intent(LoginActivity.this, UserDetailsActivity.class);
                               LoginActivity.this.startActivity(intent);


                           } else {

                               AlertDialog.Builder builder = new AlertDialog.Builder(LoginActivity.this);
                               builder.setMessage("Login Failed")
                                       .setNegativeButton("Retry", null)
                                       .create()
                                       .show();

                           }
                       } catch (JSONException e) {
                           e.printStackTrace();
                       }

                   }
               };
               LoginRequest loginRequest = new LoginRequest(username, password, responseListener);
               RequestQueue queue = Volley.newRequestQueue(LoginActivity.this);
               queue.add(loginRequest);
           //}

        }
    });


}

import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.toolbox.StringRequest;

import java.util.HashMap;
import java.util.Map;

public class LoginRequest extends StringRequest {

private static final String LOGIN_REQUEST_URL = "http://127.0.0.1/Login.php";
private Map<String, String> params;

public LoginRequest(String username, String password, Response.Listener<String> listener){
    super(Request.Method.POST, LOGIN_REQUEST_URL, listener, null);
    params = new HashMap<>();
    params.put("username", username);
    params.put("password", password);
}

@Override
public Map<String, String> getParams(){
    return params;
}
}

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