MainActivity.java

final EditText firstname, lastname, age;
        Button insert, show;
        final RequestQueue requestQueue;
        final String insertUrl = "http://192.168.1.65/tutorial/insertStudent.php";
        final String showUrl = "http://192.168.1.65/tutorial/showStudents.php";
        final TextView result;


            firstname = (EditText) findViewById(R.id.editText);
            lastname = (EditText) findViewById(R.id.editText2);
            age = (EditText) findViewById(R.id.editText3);
            insert = (Button) findViewById(R.id.insert);
            show = (Button) findViewById(R.id.showstudents);
            result = (TextView) findViewById(R.id.textView);



            requestQueue = Volley.newRequestQueue(getApplicationContext());

            show.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View view) {
                    System.out.println("ww");
                    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST,
                            showUrl, new Response.Listener<JSONObject>() {
                        @Override
                        public void onResponse(JSONObject response) {
                            System.out.println(response.toString());
                            try {
                                JSONArray students = response.getJSONArray("students");
                                for (int i = 0; i < students.length(); i++) {
                                    JSONObject student = students.getJSONObject(i);

                                    String firstname = student.getString("firstname");
                                    String lastname = student.getString("lastname");
                                    String age = student.getString("age");

                                    result.append(firstname + " " + lastname + " " + age + " \n");
                                }
                                result.append("===\n");

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

                        }
                    }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {
                            System.out.append(error.getMessage());

                        }
                    });
                    requestQueue.add(jsonObjectRequest);
                }
            });

            insert.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    StringRequest request = new StringRequest(Request.Method.POST, insertUrl, new Response.Listener<String>() {
                        @Override
                        public void onResponse(String response) {

                            System.out.println(response.toString());
                        }
                    }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {

                        }
                    }) {

                        @Override
                        protected Map<String, String> getParams() throws AuthFailureError {
                            Map<String, String> parameters = new HashMap<String, String>();
                            parameters.put("firstname", firstname.getText().toString());
                            parameters.put("lastname", lastname.getText().toString());
                            parameters.put("age", age.getText().toString());

                            return parameters;
                        }
                    };
                    requestQueue.add(request);
                }

            });


        }
    }