工廠模式提供了建立物件的最佳方式，建立物件時不會向客戶端暴露建立邏輯，並且通過一個共同的介面指向新建立的物件。

1、建立一個介面

public interface Shape {
    void draw();
}

2、具體的物件

public class Circle implements Shape {
    @Override
    public void draw() {
        System.out.println("Inside Circle::draw() method.");
    }
}

public class Rectangle implements
 
 Shape {
    @Override
    public void draw() {
        System.out.println("Inside Rectangle::draw() method.");
    }
}

public class Square implements Shape {
    @Override
    public void draw() {
        System.out.println("Inside Square::draw() method.");
    }
}

3、定義工廠類

public class ShapeFactory {
    
    
 
public Shape getShape(String shapeType) {
        if (null == shapeType) {
            return null;
        }

        switch (shapeType) {
            case "CIRCLE":
                return new Circle();
            case "RECTANGLE":
                return new Rectangle();
            case "SQUARE":
                
 
return new Square();
            default:
                return null;
        }
    }
}

4、測試

public class _Test {
    public static void main(String[] args) {
        ShapeFactory factory = new ShapeFactory();
        Shape shape1 = factory.getShape("CIRCLE");
        shape1.draw();
        Shape shape2 = factory.getShape("RECTANGLE");
        shape2.draw();
        Shape shape3 = factory.getShape("SQUARE");
        shape3.draw();
    }
}