SQLite under android developing

package cn.youhap.sqlite;

import java.io.File;

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

public class SqliteTestDrive extends Activity {
    Button addButton;
    Button deleteButton;
    Button updateButton;
    Button createDBButton;
    Button dropDBButton;
    Button queryButton;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        createDBButton = (Button)findViewById(R.id.createDBButton);
        addButton = (Button)findViewById(R.id.addButton);
        deleteButton = (Button)findViewById(R.id.deleteButton);
        updateButton = (Button)findViewById(R.id.updateButton);

        dropDBButton = (Button)findViewById(R.id.dropDBButton);
        queryButton = (Button)findViewById(R.id.queryButton);

        createDBButton.setOnClickListener(new CreateDatabaseListener());
        addButton.setOnClickListener(new AddDatabaseListener());
        updateButton.setOnClickListener(new UpdateDatabaseListener());
        queryButton.setOnClickListener(new QueryDatabaseListener());
        deleteButton.setOnClickListener(new DeleteDatabaseListener());
        dropDBButton.setOnClickListener(new DropDatabaseListener());
    }


    class CreateDatabaseListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            DatabaseHelper helper = new DatabaseHelper(SqliteTestDrive.this, "test_database");
            helper.getWritableDatabase();
        }

    }

    class AddDatabaseListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            DatabaseHelper helper = new DatabaseHelper(SqliteTestDrive.this, "test_database");
            SQLiteDatabase db = helper.getWritableDatabase();
            ContentValues value = new ContentValues();
            value.put("id", 1);
            value.put("name", "liujun");
            db.insert("user", null, value);
        }

    }

    class UpdateDatabaseListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            DatabaseHelper helper = new DatabaseHelper(SqliteTestDrive.this, "test_database");
            SQLiteDatabase db = helper.getWritableDatabase();
            ContentValues value = new ContentValues();
            value.put("name", "whm");
            db.update("user", value, "id=?", new String [] {"1"});
        }

    }

    class QueryDatabaseListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            DatabaseHelper helper = new DatabaseHelper(SqliteTestDrive.this, "test_database");
            SQLiteDatabase db = helper.getReadableDatabase();

            db.query("user", new String [] {"name"}, "id=?", new String [] {"1"}, null, null, null);

            Cursor cursor = db.query("user", new String [] {"id", "name"}, "id=?", new String [] {"1"}, null, null, null);
            while (cursor.moveToNext()){
                System.out.println(cursor.getString(cursor.getColumnIndex("name")));
            }
        }

    }

    class DeleteDatabaseListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            DatabaseHelper helper = new DatabaseHelper(SqliteTestDrive.this, "test_database");
            SQLiteDatabase db = helper.getWritableDatabase();
            db.delete("user", "id=?", new String [] {"1"});
        }

    }


    class DropDatabaseListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            DatabaseHelper helper = new DatabaseHelper(SqliteTestDrive.this, "test_database");
            SQLiteDatabase db = helper.getWritableDatabase();

            db.close();
            String packageName = "/data/data/" + this.getClass().getPackage().getName();
            File file = new File(packageName + "/databases/test_database");
            if (file.exists()){
                boolean b = file.delete();
                System.out.println(b);
            }else{
                System.out.println("can not found the file.");
            }
        }

    }
}

package cn.youhap.sqlite;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final int VERSION = 1;
    public DatabaseHelper(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
    }


    public DatabaseHelper(Context context, String name, int version){
        this(context, name, null, version);
    }

    public DatabaseHelper(Context context, String name){
        this(context, name, VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table user(id int(10), name varchar(20))");
        System.out.println("-------------------------->table is created.");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        System.out.println("-------------------------->update database.");
    }

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=""
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    />
<Button android:text="create database" android:id="@+id/createDBButton" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
<Button android:text="add" android:id="@+id/addButton" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
<Button android:text="update" android:id="@+id/updateButton" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
<Button android:text="query" android:id="@+id/queryButton" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
<Button android:text="delete" android:id="@+id/deleteButton" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
<Button android:text="drop database" android:id="@+id/dropDBButton" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
</LinearLayout>