工厂或简单工厂设计模式

现实世界中的工厂

目的

何时应考虑使用工厂模式？

创建工厂模式的算法或步骤

步骤 1：创建通用接口或抽象类

步骤 2：通过实现/扩展接口/抽象类来创建具体类

步骤 3：创建工厂类并提供创建对象的的方法

步骤 4：创建客户端并使用工厂

示例

<code class="language-java">
// Step 1: Create common interface or abstract class
public interface Shape {
}

// Step 2: Create concreate classes by implementing/extending interace/abstract class
public class Circle implementes Shape {
}

public class Square implements Shape {
}

// Step 3: Create the factory class and provide methods to create the object
public class ShapeFactory {
    private static final String CIRCLE = "circle";
    private static final String SQUARE = "square";

    public Shape createShape(String shape) {
        if(CIRCLE.equals(shape)) {
            return new Circle();
        }         
        if(SQUARE.equals(shape)) {
            return new Square();
        } 
        return null;        
    }
}

// Step 4: Create the clients and use the factory
public class Canvas {
    private ShapeFactory factory;

    public Canvas(ShapeFactory factory) {
        this.factory = factory;
    }

    public void drawShape(String shapeType) {
        Shape shape = factory.createShape(shapeType);
        
        // draw the shape, etc.
    }
}
</code>

优点

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