类别:
Creational Pattern
问题/动机
如何创建一套子类的问题(父类引用指向子类实例)
情形1:一个方法返回一个具体的子类
极端情况:1万个子类需要一万个方法吗
极端情况:如过再扩展一万个子类,还需要再增加一万个方法吗
极端情况:虽然有一万个子类,但只需要用到其中一个,其他9999个干陪着吗
情形2:一个方法返回一个父类
不管有多少子类,都可以用一个方法将其返回,可以通过一定的策略和配置文件达到不修改client的目的
方案
示例
/* 测试方法 */ public class FactoryPatternDemo { public static void main(String[] args) { Shape shape1 = ShapeFactory.getShape("CIRCLE"); shape1.draw(); Shape shape2 = ShapeFactory.getShape("RECTANGLE"); shape2.draw(); Shape shape3 = ShapeFactory.getShape("SQUARE"); shape3.draw(); } } /* 工厂返回类型,子类对象赋给父类引用 (向上转型) */ interface Shape { void draw(); } /* 矩形 */ class Rectangle implements Shape { @Override public void draw() { System.out.println("Inside Rectangle::draw() method."); } } /* 正方形 */ class Square implements Shape { @Override public void draw() { System.out.println("Inside Square::draw() method."); } } /* 圆 */ class Circle implements Shape { @Override public void draw() { System.out.println("Inside Circle::draw() method."); } } /* 简单工厂 */ class ShapeFactory { public static 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; } }
Inside Circle::draw() method. Inside Rectangle::draw() method. Inside Square::draw() method.
优化
抽象工厂模式
关键词
向上转型,简单参数
应用
package org.slf4j; [...] public final class LoggerFactory { [...] public static Logger getLogger(String name) { ILoggerFactory iLoggerFactory = getILoggerFactory(); return iLoggerFactory.getLogger(name); } [...] }
补充
静态工厂方法,见《Effective Java》
获取加密算法:
https://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#KeyPairGenerator
import java.security.KeyPairGenerator; import java.security.NoSuchAlgorithmException; public class Test { public static void main(String[] args) throws NoSuchAlgorithmException { KeyPairGenerator instance = KeyPairGenerator.getInstance("RSA"); } }
获取证书工厂:
https://docs.oracle.com/javase/7/docs/api/java/security/cert/CertificateFactory.html
import java.security.cert.CertificateFactory; public class Test { public static void main(String[] args) throws Exception { CertificateFactory instance = CertificateFactory.getInstance("X.509"); } }
获取MXBean
java.lang.management.ManagementFactory.getMemoryMXBean()
标签:draw,pattern,class,Factory,method,Shape,子类,public From: https://www.cnblogs.com/zno2/p/6694783.html