android - ratingBar

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="fill_parent"
    android:layout_height="fill_parent"
    tools:context=".MainActivity"
    android:orientation="vertical">

    <RatingBar
        android:id="@+id/ratingBar1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <RatingBar
        android:id="@+id/ratingBar2"
        style="?android:attr/ratingBarStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:numStars="10"
        android:stepSize="1" />
    <RatingBar
        android:id="@+id/ratingBar3"
        style="?android:attr/ratingBarStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:rating="1.5"/>

    <Button
        android:id="@+id/btnInc"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="증가시키기" />
    <Button
        android:id="@+id/btnDec"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="감소시키기" />
</LinearLayout>

package com.example.it.myapplication8_3;

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

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final RatingBar rating1, rating2, rating3;
        Button btnInc, btnDec;

        rating1 = (RatingBar) findViewById(R.id.ratingBar1);
        rating2 = (RatingBar) findViewById(R.id.ratingBar2);
        rating3 = (RatingBar) findViewById(R.id.ratingBar3);
        btnInc = (Button) findViewById(R.id.btnInc);
        btnDec = (Button) findViewById(R.id.btnDec);

        btnInc.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                rating1.setRating(rating1.getRating() + rating1.getStepSize());
                rating2.setRating(rating2.getRating() + rating2.getStepSize());
                rating3.setRating(rating3.getRating() + rating3.getStepSize());
            }
        });
        btnDec.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                rating1.setRating(rating1.getRating() - rating1.getStepSize());
                rating2.setRating(rating2.getRating() - rating2.getStepSize());
                rating3.setRating(rating3.getRating() - rating3.getStepSize());
            }
        });
    }
}