Android DatePicker

package com.neddy;

import java.util.Calendar;

import android.app.Activity;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.TextView;

public class HelloDatePicker extends Activity
{
    private TextView mDateDisplay;
    private Button mPickDate;
    private int mYear;
    private int mMonth;
    private int mDay;
    
    static final int DATE_DIALOG_ID = 0;
    
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        mDateDisplay=(TextView)findViewById(R.id.dateDisplay);
        mPickDate=(Button)findViewById(R.id.pickDate);
        
        mPickDate.setOnClickListener(new View.OnClickListener()
        {            
            public void onClick(View v)
            {
                showDialog(DATE_DIALOG_ID);
            }
        });
        final Calendar c=Calendar.getInstance();
        mYear=c.get(Calendar.YEAR);
        mMonth=c.get(Calendar.MONTH);
        mDay=c.get(Calendar.DAY_OF_MONTH);
        
        updateDisplay();
        
    }

    private void updateDisplay()
    {
        mDateDisplay.setText(
                new StringBuilder()
                    .append(mYear).append("-")
                    .append(mMonth+1).append("-")
                    .append(mDay).append(" "));
    }
    private DatePickerDialog.OnDateSetListener mDateSetListener = new DatePickerDialog.OnDateSetListener() 
    {                
        public void onDateSet(DatePicker view, int year,int monthOfYear, int dayOfMonth)
        {                    
            mYear = year;                    
            mMonth = monthOfYear;                    
            mDay = dayOfMonth;                    
            updateDisplay();                
        }            
    };
    
    protected Dialog onCreateDialog(int id) 
    {    
        switch (id)
        {    
            case DATE_DIALOG_ID:       
                return new DatePickerDialog(this,mDateSetListener, mYear, mMonth, mDay);
        }    
        return null;
    }
    
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    >
<TextView 
    android:id="@+id/dateDisplay" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    />
<Button 
    android:id="@+id/pickDate"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Change the date"
    />
</LinearLayout>