android使用SQLite的一个简单实例(User、UserDao、工具类DBHelp)。使用SQLite数据库：DBHelp继承SQLiteOpenHelper，必须实现其中的三个方法，其中onCreate只会执行一次，初级版本建表，其中版本更新后，表变动会自动调用onUpgrade方法

DBHelp.java

package com.mei.util;

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

public class DBHelp extends SQLiteOpenHelper{

  private static final String DATABASE_NAME = "mysqlitedb";
	
	public DBHelp(Context context) {
		super(context, DATABASE_NAME, null, 1);
	}

	@Override
	public void onCreate(SQLiteDatabase db) {
		String sql = "create table t_user(_id integer primary key autoincrement,username text,password text)";
		db.execSQL(sql);
	}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		
	}

}

User.java

package com.mei.entity;

public class User {
    private int id;
	private String username;
	private String password;
	
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	
}

UserDao.java

package com.mei.dao;

import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.mei.entity.User;
import com.mei.util.DBHelp;

public class UserDao {
  private DBHelp dbHelp;
	private SQLiteDatabase db;
	
	public UserDao(Context context){
		dbHelp = new DBHelp(context);
	}
	
	public void save(User user){
		db = dbHelp.getWritableDatabase();
		String sql = "insert into t_user(username,password) values(?,?)";
		db.execSQL(sql, new String[]{user.getUsername(),user.getPassword()});
		db.close();
	}
	
	public void update(User user){
		db = dbHelp.getWritableDatabase();
		String sql = "update t_user set username = ?,password = ? where _id = ?";
		db.execSQL(sql,new Object[]{user.getUsername(),user.getPassword(),user.getId()});
		db.close();
	}
	
	public void del(int id){
		db = dbHelp.getWritableDatabase();
		String sql = "delete from t_user where _id = ?";
		db.execSQL(sql,new Object[]{id});
		db.close();
	}
	
	public List<User> findAll(){
		List<User> list = new ArrayList<User>();
		
		db = dbHelp.getReadableDatabase();
		String sql = "select _id,username,password from t_user";
		Cursor cursor = db.rawQuery(sql, null);
		while(cursor.moveToNext()){
			User user = new User();
			user.setId(cursor.getInt(cursor.getColumnIndex("_id")));
			user.setUsername(cursor.getString(cursor.getColumnIndex("username")));
			user.setPassword(cursor.getString(cursor.getColumnIndex("password")));
			list.add(user);
		}
		db.close();
		return list;
	}
	
	public User findByID(int id){
		User user = null;
		db = dbHelp.getReadableDatabase();
		String sql = "select _id,username,password from t_user where _id = ?";
		Cursor cursor = db.rawQuery(sql, new String[]{String.valueOf(id)});
		
		while(cursor.moveToNext()){
			user = new User();
			user.setId(cursor.getInt(cursor.getColumnIndex("_id")));
			user.setUsername(cursor.getString(cursor.getColumnIndex("username")));
			user.setPassword(cursor.getString(cursor.getColumnIndex("password")));
		}
		
		db.close();
		return user;
	}
	
}