Error:NullPointerException when put button.setOnclickListener in onResponse method : <p>When i click my button in my activity, it will stop and show an error like this :</p>

<pre><code>Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
</code></pre>

<p>In my activity, i put button.setOnclickListener in onResponse() method from Response.Listener. I do this because i want to get the data from JSONObject and use that data when i click my button.</p>

<p>Sorry, I'm not too fluent in English :)</p>

<p>My activity code:</p>

<pre><code>public class MenuDaftarNilai2 extends AppCompatActivity {

    TextView tvMatkulDN, tvKlpDN, tvMhsDN;
    Button bUasDN;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_menu_daftar_nilai2);

        tvMatkulDN = (TextView) findViewById(R.id.tvMatkulDN) ;
        tvKlpDN = (TextView) findViewById(R.id.tvKlpDN) ;
        tvMhsDN = (TextView) findViewById(R.id.tvMhsDN) ;

        bUasDN = (Button) findViewById(R.id.bUasDN) ;


        Intent intent = getIntent();
        final String nama_matkul = intent.getStringExtra("nama_matkul");
        final String nama_klp = intent.getStringExtra("nama_klp");
        final String nama_mhs = intent.getStringExtra("nama_mhs");

        tvMatkulDN.setText(nama_matkul);
        tvKlpDN.setText(nama_klp);
        tvMhsDN.setText(nama_mhs);

        Response.Listener responseListener1 = new Response.Listener&lt;String&gt;() {

            @Override
            public void onResponse(String response) {

                try {

                    JSONObject jsonResponse = new JSONObject(response);

                    final String nilai_uas = jsonResponse.getString("nilai_uas");
                    final String id_uas = jsonResponse.getString("id_uas");

                    bUasDN.setText("Nilai Uas :  " + nilai_uas);
                    bUasDN.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {

                            Intent intent = new Intent(MenuDaftarNilai2.this, EditUas.class);

                            intent.putExtra("nilai_uas", nilai_uas);
                            intent.putExtra("nama_matkul", nama_matkul);
                            intent.putExtra("nama_klp", nama_klp);
                            intent.putExtra("nama_mhs", nama_mhs);
                            intent.putExtra("id_uas", id_uas);

                            MenuDaftarNilai2.this.startActivity(intent);
                            finish();

                        }
                    });


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

            }
        };
        ResponUas resUas = new ResponUas(nama_klp,nama_mhs, responseListener1);
        RequestQueue queue1 = Volley.newRequestQueue(MenuDaftarNilai2.this);
        queue1.add(resUas);
</code></pre>

<p>My XML code:</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".LoginAsis.MenuAsisten.MenuDaftarNilai.MenuDaftarNilai2"
    android:background="#ad4f4f"&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Nama Mata Kuliah"
        android:id="@+id/textView54"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:textColor="#ffffff" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Nama Kelompok"
        android:id="@+id/textView58"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/textView54"
        android:layout_alignParentLeft="true"
        android:textColor="#ffffff" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Nama Mahasiswa"
        android:id="@+id/textView59"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/textView58"
        android:layout_alignParentLeft="true"
        android:textColor="#ffffff" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=":"
        android:id="@+id/textView60"
        android:textColor="#ffffff"
        android:layout_alignParentTop="true"
        android:layout_alignLeft="@+id/textView61"
        android:layout_alignStart="@+id/textView61" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:text=":"
        android:id="@+id/textView61"
        android:textColor="#ffffff"
        android:layout_below="@+id/textView60"
        android:layout_alignLeft="@+id/textView62"
        android:layout_alignStart="@+id/textView62" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:text=":"
        android:id="@+id/textView62"
        android:textColor="#ffffff"
        android:layout_marginLeft="68dp"
        android:layout_marginStart="40dp"
        android:layout_below="@+id/textView61"
        android:layout_toRightOf="@+id/textView54"
        android:layout_toEndOf="@+id/textView54" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:text="Medium Text"
        android:id="@+id/tvMatkulDN"
        android:layout_alignTop="@+id/textView60"
        android:layout_toRightOf="@+id/textView60"
        android:textColor="#ffffff"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:text="Medium Text"
        android:id="@+id/tvKlpDN"
        android:layout_below="@+id/tvMatkulDN"
        android:layout_toRightOf="@+id/textView60"
        android:textColor="#ffffff"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" /&gt;

    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:text="Medium Text"
        android:id="@+id/tvMhsDN"
        android:layout_below="@+id/tvKlpDN"
        android:layout_toRightOf="@+id/textView61"
        android:textColor="#ffffff"
        android:layout_alignRight="@+id/tvKlpDN"
        android:layout_alignEnd="@+id/tvKlpDN"
         /&gt;

    &lt;Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Belum ada nilai uas"
        android:id="@+id/bUasDN"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_below="@id/textView59"
        android:gravity="left|center_vertical"
        android:drawableRight="@drawable/ic_create_black_24dp"/&gt;
&lt;/RelativeLayout&gt;
</code></pre>
