PITCHME.md

Annotation Processing

Jintin

---

What is Annotation

• Syntactic metadata
• Used for Class, Method, Parameter, Variable...
• Different scope for different purpose

---

Custom Annotation Example

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Tweezable {
}

---

@Retention

Life cycle of Annotation

• SOURCE
• CLASS
• RUNTIME

---

@Target

Define the type which can be annotated.

• TYPE
• FIELD
• METHOD
• PARAMETER
• CONSTRUCTOR
• LOCAL_VARIABLE
• ANNOTATION_TYPE
• PACKAGE

---

What Annotation Processing do

• Annotate in source code
• Compile
• Generate Code

---

Example

Implement Simple Factory pattern

---

Simple Factory

• Separate of Concerns
• Hide instantiate logic
• Communicate on interface

---

Interface

public interface Animal {
    void bark();
}

---

Implementation

public class Cat implements Animal {
    @Override
    public void bark() { }
}

public class Dog implements Animal {
    @Override
    public void bark() { }
}

---

Factory

public class AnimalFactory {
    public static Animal createAnimal(String type) {
        switch (type) {
            case "cat":
                return new Cat();
            case "dog":
                return new Dog();
        }
        throw new RuntimeException("not support type");
    }
}

---

Usage

public class Test {
    public static void main(String args) {
        Animal cat = AnimalFactory.createAnimal("cat");
        cat.bark();
    }
}

---

Demo

Rewrite