工厂模式

简单工厂:

为实现同一个接口的类创建对象,工厂类是核心类,由工厂类决定创建那个类的对象

缺点:
当需要扩展的时候,就需要创建实体类,改动工厂类,增加分支,不利于程序的扩展和维护,也违反了开放闭包的原则

public class Operation {

        public double getReslt(double a,double b);
    }

    public class OperationAdd {

        public double getReslt(double a,double b) {

            return a + b;
        }
    }

    public class OperationDelete {

        public double getReslt() {

            return a - b;
        }

    public class OperationFactory {

        private Operation operation = null;
        public Operation CreateOperation(String str) {

            switch(str) {

                case '+':

                operation = new OperationAdd();
                break;
                case '-':

                operation = new OperationDelete();
                break;
            }
            return operation;
        }
    }

工厂方法模式:

定义一个用于创建对象的接口,不再由一个工厂类去决定那个产品类被实例化,而是由抽象工厂的子类去决定

优点:
克服了简单工厂违反开放闭包的原则,降低了程序间的耦合
缺点:
每当增加一个类就需要增加一个对应的工厂类,增加额外的开发量

    public class LeiFeng{}
    public class Student extends LeiFeng{}
    public class Volunteer extends LeiFeng{}

    Interface IFactory {

        Leifeng createOperation();
    }

    public class StudentFactory implements IFactory {

        Leifeng createOperation() {

            return Student();
        }
    } 

    public class VolunteerFactory implements IFactory {

        Leifeng createOperation() {

            return Volunteer();
        }
    }

抽象工厂模式

提供一个创建一系列相关或者相互依赖的对象的接口,而无需指定它们的具体的类(针对的抽象的产品有多个,是一些列产品,当只有一个产品时,就退化到了工厂模式)

优点:在于方便的交换系列产品,比如:数据库的使用(Sql Server,Access),网络请求框架的使用
缺点:当需要增加功能时,改动比较大

public Inteface IDepartment {

    void insert(Department department);
    Department getDepartment(int userId);
}

public class SqlServerDepartment implements IDepartment {

    void insert(Department department) {}
    Department getDepartment(int userId) {}
}


public class AccessDepartment implements IDepartment {

    void insert(Department department) {}
    Department getDepartment(int userId) {}
}

public Inteface IUser {

    void insert(Department department);
    User getUser(int userId);
}

public class SqlServerUser implements IUser {

    void insert(User user) {}
    User getUser(int userId) {}
}

public class AccessUser implements IUser {

    void insert(User user) {}
    User getUser(int userId) {}
}

public Inteface IFactory {

    IUser createUser();
    IDepartment createDepartment();
}

public class SqlServerFactory implements IFactory {

    public IUser createUser() {

        return new SqlServerUser();
    }

    IDepartment createDepartment() {

        return new SqlServerUser();
    }
}

public class AccessFactory implements IFactory {

    public IUser createUser() {

        return new AccessUser();
    }

    IDepartment createDepartment() {

        return new AccessDepartment();
    }
}