设计模式-创建型模式-工厂模式（工厂三兄弟）
工厂模式分为简单工厂，工厂方法，抽象工厂。

简单工厂模式

一个接口，三个具体类，一个工厂，通过选择，生产出对应的对象。

package demo2;

public class Circle implements Shape{
    public Circle() {
        
    }

    @Override
    public void draw() {        
    }
    
}

package demo2;

public class Rectangle implements Shape{
    public Rectangle() {
        
    }
    
    @Override
    public void draw() {        
    }

}

package demo2;

public interface Shape {
    void draw();
}

package demo2;

public class ShapeFactory {
    public static Shape getShape(String shapeType) {
        if(shapeType == null) {
            return null;
        }
        
        if (shapeType == "Circle") {
            return new Circle();
        }
        
        if (shapeType == "Rectangle") {
            return new Rectangle();
        }
        
        if (shapeType == "Square") {
            return new Square();
        }
        return null;
    }
}

package demo2;

public class Square implements Shape{
    public Square() {
        
    }

    @Override
    public void draw() {        
    }
}

package demo2;

public class Test {
    public static void main(String[] agrs) {
        Shape circle = new ShapeFactory().getShape("Circle");
        circle.draw();
    }
}

利用反射改进工厂模式

由于违反开放-封闭原则，每次都要去修改源代码，所以直接使用反射机制。
将类传入，使用泛型+反射，生产出对象。

package demo2;

public class ShapeFactory2 {
    @SuppressWarnings("deprecation")
    public static Object getClass(Class<? extends Shape> clazz) {    // 代表通配的是Shape的子类，即都为借口的子类
        Object obj = null;
        
            try {
                obj = Class.forName(clazz.getName()).newInstance();
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        return obj;
        
    }
}

package demo2;

public class Test {
    public static void main(String[] agrs) {
        Shape circle = (Circle)ShapeFactory2.getClass(Circle.class);
        circle.draw();
    }
}

工厂方法

每个对象有对应的工厂，将原先的工厂拆分。

package demo2;

public class CircleFactory implements Factory{

    @Override
    public Shape getShape() {
        return new Circle();
    }

}

package demo2;

public class RectangleFactory implements Factory{

    @Override
    public Shape getShape() {
        return new Rectangle();
    }

}

package demo2;

public class SquareFactory implements Factory{

    @Override
    public Shape getShape() {
        return new Square();
    }

}

package demo2;

public class Test {
    public static void main(String[] agrs) {
        Factory circleFactory = new CircleFactory();
        Shape circle = circleFactory.getShape();
        circle.draw();
    }
}

抽象工厂

两个抽象接口，一个为产品，一个为工厂，进行生产

产品

枪

public interface Gun{
    public void shooting();
}

子弹

public interface Bullet{
    public void load();
}

ak类

public class AK implements Gun{
    @Override
    public void shooting(){};
}

对应子弹

public class AK_Bullet implements Bullet{
    @Override
    public void load(){};
}

m4

public class M4 implements Gun{
    @Override
    public void shooting(){};
}

对应子弹

public class M4_Bullet implements Bullet{
    @Override
    public void load(){};
}

工厂

public interface Factory{
    public Gun produceGun();
    public Bullet produceBullet();
}

具体工厂
ak

public class AK_Factory implements Factory {
    @Override
    public Gun produceGun(){
        return new AK();
    }
    @Override
    public Bullet produceBullet(){
        return new AK_Bullete();
    }
}

M4

public class M4_Factory implements Factory{
    @Override
    public Gun produceGun(){
        return new M4();
    }
    @Override
    public Bullet produceBullet(){
        return new M4_Bullet();
    }
}

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