Android使用的是SQLite数据库系统。为一人应用程序所创建的数据库只能被此应用程序访问，其他应用程序将不能访问它。以编程方式创建的SQLite数据库总是存储在/data/data/<package_name>/databases文件夹下。

一、创建数据库辅助类

package com.example.androidtest;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

/**
 * 访问数据库的辅助类
 * 封装了访问数据的所有复杂性。
 * 为一个应用程序所创建的数据库只能被此应用程序访问，其他应用程序将不能访问它。
 * 数据库文件存储在/data/data/<package_name>/databases文件夹下。
 * @author Administrator
 *
 */
public class DBAdapter {
	static final String KEY_ROWID = "_id";
	static final String KEY_NAME = "name";
	static final String KEY_EMAIL = "email";
	static final String TAG = "DBAdapter";
	
	static final String DATABASE_NAME = "MyDB";
	static final String DATABASE_TABLE = "contacts";
	static final int DATABASE_VERSION = 1;
	
	//定义创建表的sql语句常量
	static final String DATABASE_CREATE =
			"create table contacts (_id integer primary key autoincrement, "
			+ "name text not null, email text not null);";
	
	final Context context;
	
	DatabaseHelper DBHelper;
	SQLiteDatabase db;
	
	public DBAdapter(Context ctx)
	{
		this.context = ctx;
		DBHelper = new DatabaseHelper(context);
	}
	
	private static class DatabaseHelper extends SQLiteOpenHelper
	{
		DatabaseHelper (Context context)
		{
			super(context, DATABASE_NAME, null, DATABASE_VERSION);
		}

		@Override
		public void onCreate(SQLiteDatabase db) {
			try {
				db.execSQL(DATABASE_CREATE);
			} catch (SQLException e){
				e.printStackTrace();
			}
		}

		@Override
		public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
			Log.w(TAG, "Upgrading database from version "+oldVersion + "to "
					+newVersion+", which will destroy all old data");
			//为了简单起见，直接删除现有的表并创建一个新表，在实际中，通常需要备份现在的表，
			//然后将其内容复制到新表中。
			db.execSQL("DROP TABLE IF EXISTS contacts");
			onCreate(db);
		}
	}
	
	/**
	 * 创建or打开数据库
	 * @return
	 * @throws SQLException
	 */
	public DBAdapter open() throws SQLException
	{
		db = DBHelper.getWritableDatabase();
		return this;
	}
	
	/**
	 * 关闭数据库
	 */
	public void close()
	{
		DBHelper.close();
	}
	
	/**
	 * 插入数据
	 * @param name
	 * @param email
	 * @return ID
	 */
	public long insertContact(String name, String email)
	{
		ContentValues initialValues = new ContentValues();
		initialValues.put(KEY_NAME, name);
		initialValues.put(KEY_EMAIL, email);
		return db.insert(DATABASE_TABLE, null, initialValues);
	}
	
	/**
	 * 删除数据
	 * @param rowId
	 * @return	true:删除成功
	 */
	public boolean deleteContact(long rowId)
	{
		return db.delete(DATABASE_TABLE, KEY_ROWID+"="+rowId, null) > 0;
	}
	
	/**
	 * 查询所有数据
	 * @return Cursor	游标(可看成指向结果集的指针)
	 */
	public Cursor getAllContacts()
	{
		String[] columns = new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL};
		return db.query(DATABASE_TABLE, columns, null, null, null, null, null);
	}
	
	/**
	 * 查询指定数据
	 * @param rowId
	 * @return	Cursor	游标(可看成指向结果集的指针)
	 * @throws SQLException
	 */
	public Cursor getContact(long rowId) throws SQLException
	{
		String[] columns = new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL};
		Cursor mCursor = db.query(true, DATABASE_TABLE, columns, KEY_ROWID+"="+rowId, null, null, null, null, null);
		if(mCursor != null) {
			mCursor.moveToFirst();
		}
		return mCursor;
	}
	
	/**
	 * 更新指定数据
	 * @param rowId
	 * @param name
	 * @param email
	 * @return	true:更新成功
	 */
	public boolean updateContact(long rowId, String name, String email)
	{
		ContentValues args = new ContentValues();
		args.put(KEY_NAME, name);
		args.put(KEY_EMAIL, email);
		return db.update(DATABASE_TABLE, args, KEY_ROWID+"="+rowId, null) > 0;
	}
}

二、创建活动

视图

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    tools:context="${relativePackage}.${activityClass}" >

    <Button
        android:id="@+id/btn_insert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Insert"
        android:onClick="onClickInsert" />
    
    <Button
        android:id="@+id/btn_query_all"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Query all"
        android:onClick="onClickQueryAll" />
    
     <Button
        android:id="@+id/btn_query_id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Query id"
        android:onClick="onClickQueryID" />
     
     <Button
        android:id="@+id/btn_update"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Update"
        android:onClick="onClickUpdate" />
     
     <Button
        android:id="@+id/btn_delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Delete"
        android:onClick="onClickDelete" />

</LinearLayout>

代码

package com.example.androidtest;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

public class DatabasesActivity extends Activity {

	DBAdapter db;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_databases);
		
		db = new DBAdapter(this);
		db.open();
	}
	
	@Override
	protected void onDestroy()
	{
		super.onDestroy();
		db.close();
	}
	
	public void onClickInsert(View view)
	{
		Log.d("test", "db="+db);
		long id = db.insertContact("Wei-MengLee", "weimenglee@qq.com");
		id = db.insertContact("Mary Jackson", "mary@qq.com");
		
		Toast.makeText(this, "Insert successful", Toast.LENGTH_SHORT).show();
	}
	
	public void onClickQueryAll(View view)
	{
		Cursor c = db.getAllContacts();
		if(c.moveToFirst()){
			do {
				DisplayContact(c);
			} while (c.moveToNext());
		}
	}
	
	public void onClickQueryID(View view)
	{
		Cursor c = db.getContact(2);
		if(c.moveToFirst()){
			DisplayContact(c);
		}else{
			Toast.makeText(this, "No contact found", Toast.LENGTH_SHORT).show();
		}
	}
	
	public void onClickUpdate(View view)
	{
		if(db.updateContact(1, "Wei-Meng Lee", "weimenglee@gmail.com")){
			Toast.makeText(this, "Update successful", Toast.LENGTH_SHORT).show();
		}else{
			Toast.makeText(this, "Update failed", Toast.LENGTH_SHORT).show();
		}
	}
	
	public void onClickDelete(View view)
	{
		if(db.deleteContact(1)){
			Toast.makeText(this, "Delete successful", Toast.LENGTH_SHORT).show();
		}else{
			Toast.makeText(this, "Delete failed", Toast.LENGTH_SHORT).show();
		}
	}
	
	public void DisplayContact(Cursor c)
	{
		Toast.makeText(this, "id: "+c.getString(0) + "\n" +
				"Name: "+c.getString(1) + "\n" +
				"Email: " + c.getString(2),
				Toast.LENGTH_SHORT).show();
	}
	
	/**
	 * 把assets目录下的一个现成sqlite文件复制到目标文件夹。
	 * 注意: assets目录下的文件必须采用小写字母格式。
	 */
	public void CopyMyDB() {
		try {
			String destPath = "/data/data/"+getPackageName()+"/databases";
			File f = new File(destPath);
			Log.d("test", "db path="+f.getAbsolutePath());
			if (!f.exists()){
				f.mkdir();
				f.createNewFile();
				CopyDB(getBaseContext().getAssets().open("mydb"),
						new FileOutputStream(destPath+"/MyDB"));
			}
		} catch (FileNotFoundException e){
			e.printStackTrace();
		} catch (IOException e){
			e.printStackTrace();
		}
	}
	
	public void CopyDB(InputStream inputStream, OutputStream outputStream) throws IOException
	{
		byte[] buffer = new byte[1024];
		int length;
		while ((length = inputStream.read(buffer)) > 0) {
			outputStream.write(buffer, 0, length);
		}
		inputStream.close();
		outputStream.close();
	}
}

运行效果