設計模式-建立型模式-工廠模式（工廠三兄弟）
工廠模式分為簡單工廠，工廠方法，抽象工廠。

簡單工廠模式

一個介面，三個具體類，一個工廠，通過選擇，生產出對應的物件。

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();
    }
}
 

利用反射改進工廠模式

由於違反開放-封閉原則，每次都要去修改原始碼，所以直接使用反射機制。
將類傳入，使用泛型+反射，生產出物件。

package demo2;

public class ShapeFactory2 {
    @SuppressWarnings("deprecation")
    public static Object getClass(Class<? extends Shape> clazz) {   // 代表通配的是Shape的子類，即都為藉口的子類
        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();
    }
}

工廠方法

每個物件有對應的工廠，將原先的工廠拆分。

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();
    }
}

抽象工廠

兩個抽象介面，一個為產品，一個為工廠，進行生產

產品

槍

public interface Gun{
    public void shooting();
}

子彈

public interface Bullet{
    public void load();
}

ak類

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

對應子彈

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

m4

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

對應子彈

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

工廠

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

具體工廠
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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