RATING BAR ANDROID STUDIO

JAVA FILE
package com.example.viraj.blog_13_ratingbar;

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

public class MainActivity extends AppCompatActivity {
private RatingBar rb1;
    private Button b1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        rb1=(RatingBar)findViewById(R.id.id_ratingBar);
        b1=(Button)findViewById(R.id.id_check);

        rb1.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {
            @Override
            public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) {
                Toast.makeText(getApplicationContext(),"STAR IS : "+ rating,Toast.LENGTH_LONG).show();
            }
        });
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(getApplicationContext(),"STAR IS : "+ rb1.getRating(),Toast.LENGTH_LONG).show();
            }
        });

    }
}

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_13_ratingbar.MainActivity">

    <RatingBar
        android:id="@+id/id_ratingBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_marginRight="8dp"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="64dp"
        app:layout_constraintBottom_toBottomOf="parent"
        android:layout_marginBottom="8dp"
        app:layout_constraintVertical_bias="0.052"
        android:numStars="5"
        android:rating="2.0"
        android:stepSize="1"
        />

    <Button
        android:id="@+id/id_check"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginTop="144dp"
        android:text="CHECK"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/ratingBar"
        app:layout_constraintVertical_bias="0.0" />
</android.support.constraint.ConstraintLayout>