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实现从Access换为使用Sqlserver，接着换为Oracle

源代码：

class User{	private int ID;	private String name;	public int getID() {		return ID;	}	public void setID(int iD) {		ID = iD;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}}class SqlserverUser{	public void Insert(User user)	{		System.out.println("在User表中增加一条记录");	}	public User GetUser(int id)	{		System.out.println("根据ID得到User表中的一条记录");		return null;	}}public class main {	public static void main(String[] args) {		User user=new User();		SqlserverUser su=new SqlserverUser();//数据库固定		su.Insert(user);		su.GetUser(1);	}}

 使用工厂模式方法：

class User{	private int ID;	private String name;	public int getID() {		return ID;	}	public void setID(int iD) {		ID = iD;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}}interface IUser{	void Insert(User user);	User GetUser(int id);}class SqlserverUser implements IUser{	public void Insert(User user)	{		System.out.println("在User表中增加一条记录");	}	public User GetUser(int id)	{		System.out.println("根据ID得到User表中的一条记录");		return null;	}}class AccessUser implements IUser{	public void Insert(User user)	{		System.out.println("在User表中增加一条记录");	}	public User GetUser(int id)	{		System.out.println("根据ID得到User表中的一条记录");		return null;	}}interface IFactory{	IUser createUser();}//定义一个创建访问User表对象的工厂接口class SqlserverFactory implements IFactory{	@Override	public IUser createUser() {		// TODO Auto-generated method stub		return new SqlserverUser();	}}class AccessFactory implements IFactory{	@Override	public IUser createUser() {		// TODO Auto-generated method stub		return new AccessUser();	}}//具体工厂类public class main {	public static void main(String[] args) {		User user=new User();		IFactory su=new SqlserverFactory();//若要修改Access数据库，只须修改此处		IUser iu=su.createUser();		iu.Insert(user);		iu.GetUser(1);	}}

 若增加一个新的表如部门表（Department表）

就要增加抽象工厂类

class User{	private int ID;	private String name;	public int getID() {		return ID;	}	public void setID(int iD) {		ID = iD;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}}class Department{	private int id;	private String deptname;	public int getId() {		return id;	}	public void setId(int id) {		this.id = id;	}	public String getDeptname() {		return deptname;	}	public void setDeptname(String deptname) {		this.deptname = deptname;	}}interface IUser{	void Insert(User user);	User GetUser(int id);}interface IDepartment{	void Insert(Department department);	Department GetDepartment(int id);}interface IFactory//IFactory接口，增加一个创建访问Department表对象的抽象接口工厂{	IUser CreateUser();	IDepartment CreateDepartment();}class SqlserverUser implements IUser{	public void Insert(User user)	{		System.out.println("在User表中增加一条记录");	}	public User GetUser(int id)	{		System.out.println("根据ID得到User表中的一条记录");		return null;	}}class SqlserverDepartment implements IDepartment{	@Override	public void Insert(Department department) {		// TODO Auto-generated method stub		System.out.println("在department表中增加一条记录");	}	@Override	public Department GetDepartment(int id) {		// TODO Auto-generated method stub		System.out.println("根据ID得到department表中的一条记录");		return null;	}}class SqlserverFactory implements IFactory{	@Override	public IUser CreateUser() {		// TODO Auto-generated method stub		return new SqlserverUser();	}	@Override	public IDepartment CreateDepartment() {		// TODO Auto-generated method stub		return new SqlserverDepartment();	}}class AccessUser implements IUser{	public void Insert(User user)	{		System.out.println("在User表中增加一条记录");	}	public User GetUser(int id)	{		System.out.println("根据ID得到User表中的一条记录");		return null;	}}class AccessDepartment implements IDepartment{	@Override	public void Insert(Department department) {		// TODO Auto-generated method stub		System.out.println("在department表中增加一条记录");	}	@Override	public Department GetDepartment(int id) {		// TODO Auto-generated method stub		System.out.println("根据ID得到department表中的一条记录");		return null;	}}class AccessFactory implements IFactory{	public IUser CreateUser() {		// TODO Auto-generated method stub		return new AccessUser();	}	@Override	public IDepartment CreateDepartment() {		// TODO Auto-generated method stub		return new AccessDepartment();	}}//客户端public class main {	public static void main(String[] args) {		User user=new User();		IFactory su=new SqlserverFactory();//只需修改此处，实现数据库访问的切换		IUser iu=su.CreateUser();		iu.Insert(user);		iu.GetUser(1);		Department dept=new Department();		IDepartment id=su.CreateDepartment();		id.Insert(dept);		id.GetDepartment(1);	}}

抽象工厂可以很方便的切换不同数据库访问的代码，但是改动量非常多。

用简单工厂改进抽象工厂，去除IFactory，SqlservserFactory和AccessFactory三个工厂类，用DataAccess类代替

class DataAccess{	private static  String db="Sqlserver";//Access			public static IUser CreatUser()			{		IUser result=null;		switch(db)		{		case "Sqlserver":			result=new SqlserverUser();break;		case "Access":			result=new AccessUser();			break;		}		return result;			}			public static IDepartment CreatDepartment()			{				IDepartment result=null;				switch(db)				{				case "Sqlserver":					result=new SqlserverDepartment();break;				case "Access":					result=new AccessDepartment();					break;				}				return result;			}}//客户端已经不需要受改动数据库访问的影响public class main {	public static void main(String[] args) {		User user=new User();		Department dept=new Department();		IUser iu=DataAccess.CreatUser();//直接得到实例，而不需要存在任何依赖		iu.Insert(user);		iu.GetUser(1);		IDepartment id=DataAccess.CreatDepartment();		id.Insert(dept);		id.GetDepartment(1);	}	//事先设置了db的值所以简单工厂的方法都不需要输入参数}

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