The factory pattern is to encapsulate object creation logic through a factory class, so that the caller does not need to care about the specific implementation class. 1. Define the unified behavior specification of interface Shape; 2. Create Circle and Rectangle implementation classes; 3. Write ShapeFactory factory class to return different instances according to parameters; 4. Use the factory class to obtain objects and call methods. This mode is suitable for scenarios where object creation is complex, the type is often changed, or the principle of opening and closing is required. It can effectively decouple the caller and specific classes and reduce maintenance costs.
Factory Design Patterns are very common in Java, especially in scenarios where decoupling object creation logic is required. It is responsible for creating different types of objects through a separate factory class, so that the caller does not need to care about the specific implementation class, but only needs to pass in parameters to get the corresponding instance.
What is the factory model?
Simply put, the factory pattern is to encapsulate the object creation process into a factory class . The advantage of this is: when you want to add new types or modify the creation method in the future, you do not need to change the call code, you just need to change the factory class.
For example, if you have an interface Shape , there are multiple implementation classes such as Circle and Rectangle . If you want to return different graphic objects according to different inputs, you can use factory mode.
Use interfaces to define behavior
First we define an interface to represent the type of object we want to create:
public interface Shape {
void draw();
}Then write a few implementation classes:
public class Circle implements Shape {
@Override
public void draw() {
System.out.println("Draw Circle");
}
}
public class Rectangle implements Shape {
@Override
public void draw() {
System.out.println("Draw Rectangle");
}
}This step is the basis, and the purpose is to unify the behavioral norms of the object.
Create a factory class
Next, we write a factory class to decide which object to create based on the input:
public class ShapeFactory {
public Shape getShape(String shapeType) {
if (shapeType == null || shapeType.isEmpty()) {
return null;
}
if (shapeType.equalsIgnoreCase("CIRCLE")) {
return new Circle();
} else if (shapeType.equalsIgnoreCase("RECTANGLE")) {
return new Rectangle();
}
return null;
}
}This factory class is very simple. It is a method that receives string parameters and returns the corresponding instance after judgment. You can expand more types according to your needs, or you can replace strings with enums to improve readability and security.
How to use factory classes?
It's also very intuitive to use:
public class FactoryPatternDemo {
public static void main(String[] args) {
ShapeFactory shapeFactory = new ShapeFactory();
// Get the Circle object and call the method Shape shape1 = shapeFactory.getShape("CIRCLE");
shape1.draw();
// Get the Rectangle object and call the method Shape shape2 = shapeFactory.getShape("RECTANGLE");
shape2.draw();
}
}The result of the operation will be:
Draw Circle Draw Rectangle
This is a complete example. As you can see, the caller does not need to know the specific class name at all. He just needs to tell the factory "What I want" to get the available objects.
Several situations where factory model is applicable
- The object creation logic is quite complicated and I don't want users to understand the details
- The types of objects in the system may change or expand frequently
- Hope to be closed for modification and open for extension (open and close principle)
If you just simply create an object, there is actually no need to use factory mode. But if multiple types, configurations, conditional judgments, etc. are involved, it is worth considering introducing them.
Basically that's it. Although the factory model is not complex in structure, it is very practical, especially suitable for early-stage architectural design. If used well, it can greatly reduce the cost of later maintenance.
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