AndroidのRatingBarコントロールの使い方

package com.example.mars_2500_ratingbar;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RatingBar;
import android.widget.RatingBar.OnRatingBarChangeListener;
import android.os.Build;

public class MainActivity extends Activity
{

    RatingBar ratingBar;
    Button button1;
    public static String TAG="MainActivity";
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ratingBar=(RatingBar)findViewById(R.id.ratingBar1);
        ratingBar.setOnRatingBarChangeListener(new RatingBarChangeListener());
        button1=(Button)findViewById(R.id.buttn1);
        button1.setOnClickListener(new ClickListener());
        
    }

    class RatingBarChangeListener implements OnRatingBarChangeListener
    {
        @Override
        public void onRatingChanged(RatingBar ratingBar, float rating,
                boolean fromUser)
        {
            Log.i(TAG, "    ="+rating);
            System.out.println("    ="+rating);
        }
    }
    
    class ClickListener implements OnClickListener
    {
        @Override
        public void onClick(View v)
        {    //    0.5 
            ratingBar.setRating(ratingBar.getRating()+0.5f);
        }
    }
    
    
    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

<?xml version="1.0" encoding="UTF-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
         android:orientation="vertical"
         android:layout_width="fill_parent"
         android:layout_height="fill_parent"
         >
 
<RatingBar 
        android:id="@+id/ratingBar1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:numStars="5"
        android:stepSize="0.5"
        />
    <Button 
        android:id="@+id/buttn1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/ratingBar1"
        android:text="  "
         />
 </LinearLayout>