Java设计模式-工厂方法模式

1：使用场景

在任何需要生产复杂对象的地方，都可以使用工厂方法模式，用new可以完成创建对象无需使用工厂方法模式

2：UML图

3：代码举例

public  abstract class Product {public abstract void method(); }

public  class ConcreteProductA extends Product{@Overridepublic  void method(){System.out.println("我是具体产品A");}}

public  class ConcreteProductB extends Product{@Overridepublic  void method(){System.out.println("我是具体产品B");}}

public  abstract class Factory {public abstract <T extends Product> T createProduct(Class<T> clz); }

public  class ConcreteFactory extends Factory{@Overridepublic  <T extends Product> T createProduct(Class<T> clz){Product p=null;try{p=(Product)Class.forName(clz.getName()).newInstance();}catch(Exception e){e.printStackTrace();}return (T)p;}}

public  class Client {public  static void main(String[] args){Factory factory =new ConcreteFactory();Product product=factory.createProduct(ConcreteProductA.class);product.method();}}

多工厂方法模式：

可以为每个产品都定义一个具体工厂，各司其职。

public  class ConcreteFactoryA extends Factory{@Overridepublic  Product createProduct(){return new ConcreteFactoryA();}}public  class ConcreteFactoryB extends Factory{@Overridepublic  Product createProduct(){return new ConcreteFactoryB();}}public  class Client {public  static void main(String[] args){Factory factoryA =new ConcreteFactoryA();Product productA=factoryA.createProduct();productA.method();                Factory factoryB =new ConcreteFactoryB();Product productB=factoryB.createProduct();productB.method();}}

简单工厂模式：

工厂类如果只有一个时，简化工厂方法模式，去掉抽象，将相应的工厂方法改为静态：

public  class Factory {@Overridepublic  static Product createProduct(){return new ConcreteFactoryA();}}

4：Android中的工厂方法模式

    /**     * Decode a file path into a bitmap. If the specified file name is null,     * or cannot be decoded into a bitmap, the function returns null.     *     * @param pathName complete path name for the file to be decoded.     * @param opts null-ok; Options that control downsampling and whether the     *             image should be completely decoded, or just is size returned.     * @return The decoded bitmap, or null if the image data could not be     *         decoded, or, if opts is non-null, if opts requested only the     *         size be returned (in opts.outWidth and opts.outHeight)     */    public static Bitmap decodeFile(String pathName, Options opts) {        Bitmap bm = null;        InputStream stream = null;        try {            stream = new FileInputStream(pathName);            bm = decodeStream(stream, null, opts);        } catch (Exception e) {            /*  do nothing.                If the exception happened on open, bm will be null.            */            Log.e("BitmapFactory", "Unable to decode stream: " + e);        } finally {            if (stream != null) {                try {                    stream.close();                } catch (IOException e) {                    // do nothing here                }            }        }        return bm;    }