关于数据库的问题

完整代码如下：
package com.ex05_02;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {
Button creatBtn,deleteBtn;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
creatBtn=(Button)findViewById(R.id.creat1);
creatBtn.setOnClickListener(new mClick());
deleteBtn=(Button)findViewById(R.id.delete1);
deleteBtn.setOnClickListener(new mClick());
}
class mClick implements OnClickListener
{
public void onClick(View arg0)
{
if(arg0 == creatBtn)
{
DBCreate db= new DBCreate();
}
else if(arg0 == deleteBtn)
{
deleteDatabase(DBCreate.Database_name);
}
}
}
class DBCreate
{
static final String Database_name = "PhoneBook.db";
private DBCreate()
{
SQLiteDatabase db;
String TABLE_NAME ="Users";
String ID = "_id";
String USER_NAME = "user_name";
String ADDRESS = "address";
String TELEPHONE = "telephone";
String MALL_ADDRESS = "mail_address";
String DATABASE_CREATE =
"CREAT TABLE" +TABLE_NAME + "("
+ ID + "INTEGER primary key autoincrement,"
+ USER_NAME + "text not null, "
+TELEPHONE+ "text not null, "
+ADDRESS+ "text not null, "
+MALL_ADDRESS + " text not null"+ ");";
int mode = Context.MODE_PRIVATE;
db = openOrCreateDatabase(Database_name, mode, null);
db.execSQL(DATABASE_CREATE);
}
}
}
粗体字哪里说db没被使用，这是怎么回事？