android button set text on click listner

JAVA FILE

package com.example.viraj.blog_2_button;

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

public class MainActivity extends AppCompatActivity {
private Button b1;
    private TextView t1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //type cast
        t1=(TextView)findViewById(R.id.id_text);
        b1=(Button)findViewById(R.id.id_button);

        //set on click listner
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                t1.setText("its working");
            }
        });

    }
}

XML FILE

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.ConstraintLayout 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"    tools:context="com.example.viraj.blog_2_button.MainActivity">

    <TextView        android:id="@+id/id_text"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Hello World!"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent"        app:layout_constraintHorizontal_bias="0.445"        app:layout_constraintVertical_bias="0.311"        android:layout_marginRight="8dp"        android:layout_marginLeft="8dp"        android:layout_marginTop="8dp" />

    <Button        android:id="@+id/id_button"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Button"        android:layout_marginTop="155dp"        app:layout_constraintTop_toBottomOf="@+id/id_text"        android:layout_marginRight="8dp"        app:layout_constraintRight_toRightOf="parent"        android:layout_marginLeft="8dp"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintHorizontal_bias="0.464" />

</android.support.constraint.ConstraintLayout>