工厂模式是一种创建对象的模式, 被广泛的应用在 jdk、 Spring 和 Status 框架中.
工厂模式根据 "输入", 应用在超类和多个子类之间的情况, 这种模式将创建对象的责任转移到工厂类.
在软件开发中, 当我们会用到大量的创建某种、某类或者某批对象时, 就会用到工厂模式。
在 《Java与模式》一书中, 被分为三类:
- 简单工厂模式: 不利于产生系列产品;
- 工厂方法模式: 多形态工厂;
- 抽象工厂模式: 又称工具箱、产品族, 不利于产生新的产品
简单工厂模式属于创建型模式, 是工厂模式的一种
简单工厂模式是由一个工厂对象决定创建出哪一种产品类的实例。简单工厂模式是工厂模式家族中最简单实用的模式
简单工厂模式: 定义了一个创建对象的类, 由这个类来封装实例化对象的行为(代码)
UML 图:
Shape: 图形的规范类(AbstractProduct)
public interface Shape {
void draw();
}Circle: 圆形的图形(Product1)
public class Circle implements Shape {
public Circle() {
this.draw();
}
@Override
public void draw() {
System.out.println("Circle.draw method.");
}
}Square: 正方形图形(Product2)
public class Square implements Shape {
public Square() {
this.draw();
}
@Override
public void draw() {
System.out.println("Square.draw method.");
}
}ShapeFactory: 绘制图形代工厂(Factory)
public class ShapeFactory {
public Shape getShape(String shapeType) {
if (shapeType == null) {
return null;
}
if (shapeType.equalsIgnoreCase("circle")){
return new Circle();
} else if (shapeType.equalsIgnoreCase("square")) {
return new Square();
}
return null;
}
}调用:
public class FactoryPatternDemo {
public static void main(String[] args) {
ShapeFactory shapeFactory = new ShapeFactory();
Shape circle = shapeFactory.getShape("circle");
Shape square = shapeFactory.getShape("square");
}
}- 优点是比较好理解, 简单易操作;
- 缺点是违反了设计模式的 ocp 模式, 即对扩展开放, 对修改关闭, 当我们给类增加新功能的时候, 尽量不修改代码, 或者尽可能少的修改代码
- 比如需要增加一个 Rectangle 的图形, 就需要把 ShapeFactory 进行修改:
public class ShapeFactory { public Shape getShape(String shapeType) { if (shapeType == null) { return null; } if (shapeType.equalsIgnoreCase("circle")){ return new Circle(); } else if (shapeType.equalsIgnoreCase("rectangle")) { return new Rectangle(); } else if (shapeType.equalsIgnoreCase("square")) { return new Square(); } return null; } }
和简单工厂模式中工厂负责生产所有产品相比，工厂方法模式将生成具体产品的任务分发给具体的产品工厂，其UML类图如下
Shape: 图形的规范类(AbstractProduct)
public interface Shape {
void draw();
}Circle: 圆形的图形(Product1)
public class Circle implements Shape {
public Circle() {
this.draw();
}
@Override
public void draw() {
System.out.println("Circle.draw method.");
}
}Square: 正方形图形(Product2)
public class Square implements Shape {
public Square() {
this.draw();
}
@Override
public void draw() {
System.out.println("Square.draw method.");
}
}AbstractFactory: 生产不同图形的工厂的抽象类
public interface AbstractFactory {
Shape makeShape();
}CircleFactory: 生产圆形的图形的工厂
public class CircleFactory implements AbstractFactory{
@Override
public Shape makeShape() {
return new Circle();
}
}SquareFactory: 生产正方形图形的工厂
public class SquareFactory implements AbstractFactory{
@Override
public Shape makeShape() {
return new Square();
}
}调用:
public class MethodFactoryPatternDemo {
public static void main(String[] args) {
CircleFactory circleFactory = new CircleFactory();
SquareFactory squareFactory = new SquareFactory();
circleFactory.makeShape();
squareFactory.makeShape();
}
}简单工厂模式 和 工厂方法模式 这两种设计模式只能针对一种类型的产品, 如果要生产颜色(多种产品), 则需要用到抽象工厂模式
Shape: 图形的规范类(AbstractProduct)
public interface Shape {
void draw();
}Circle: 圆形的图形(Product1)
public class Circle implements Shape {
public Circle() {
this.draw();
}
@Override
public void draw() {
System.out.println("Circle.draw method.");
}
}Square: 正方形图形(Product2)
public class Square implements Shape {
public Square() {
this.draw();
}
@Override
public void draw() {
System.out.println("Square.draw method.");
}
}Color: 颜色的规范类
public interface Color {
void fill();
}Blue: 蓝色
public class Blue implements Color {
public Blue() {
this.fill();
}
@Override
public void fill() {
System.out.println("Blue.fill method.");
}
}Red: 红色
public class Red implements Color {
public Red() {
this.fill();
}
@Override
public void fill() {
System.out.println("Red.fill method.");
}
}AbstractFactory: 两种规范接口的抽象接口
public abstract class AbstractFactory {
public abstract Color getColor(String colorType);
public abstract Shape getShape(String shapeType) ;
}ShapeFactory: 生产图形的工厂
public class ShapeFactory extends AbstractFactory {
@Override
public Shape getShape(String shapeType){
if(shapeType == null){
return null;
}
if(shapeType.equalsIgnoreCase("CIRCLE")){
return new Circle();
} else if(shapeType.equalsIgnoreCase("RECTANGLE")){
return new Rectangle();
} else if(shapeType.equalsIgnoreCase("SQUARE")){
return new Square();
}
return null;
}
@Override
public Color getColor(String color) {
return null;
}
}ColorFactory: 生产颜色的工厂
public class ColorFactory extends AbstractFactory {
@Override
public Shape getShape(String shapeType){
return null;
}
@Override
public Color getColor(String color) {
if(color == null){
return null;
}
if(color.equalsIgnoreCase("RED")){
return new Red();
} else if(color.equalsIgnoreCase("GREEN")){
return new Green();
} else if(color.equalsIgnoreCase("BLUE")){
return new Blue();
}
return null;
}
}FactoryProducer: 工厂生成器, 用来传递形状、颜色信息来获取工厂
public class FactoryProducer {
public static AbstractFactory getFactory(String choice){
if(choice.equalsIgnoreCase("SHAPE")){
return new ShapeFactory();
} else if(choice.equalsIgnoreCase("COLOR")){
return new ColorFactory();
}
return null;
}
}AbstractFactoryPatternDemo: 调用代码
public class AbstractFactoryPatternDemo {
public static void main(String[] args) {
//获取形状工厂
AbstractFactory shapeFactory = FactoryProducer.getFactory("SHAPE");
//获取形状为 Circle 的对象
shapeFactory.getShape("CIRCLE");
//获取形状为 Rectangle 的对象
shapeFactory.getShape("RECTANGLE");
//获取形状为 Square 的对象
shapeFactory.getShape("SQUARE");
//获取颜色工厂
AbstractFactory colorFactory = FactoryProducer.getFactory("COLOR");
//获取颜色为 Red 的对象
colorFactory.getColor("RED");
//获取颜色为 Green 的对象
colorFactory.getColor("Green");
//获取颜色为 Blue 的对象
colorFactory.getColor("BLUE");
}
}