My Java Annotation Example

Main.java

package my;

import java.lang.reflect.Field;
import my.annotation.MyColumn;

public class Main {

	public static void main(String[] args) {
		MyObject o = new MyObject("Jonathan", "Jo", "GREEN");
		//อีกเทคนิคหนึ่งที่ใช้ร่วมกับ Annotation คือ reflect เพื่อเรียกดูข้อมูลของ Class
		Class klazz = o.getClass();
		//ดู field ทั้งหมดที่ประกาศ
		for (Field f : klazz.getDeclaredFields()) {
			MyColumn myCol = f.getAnnotation(MyColumn.class);
			if (myCol != null)
				System.out.println(
					"anno_name:" + myCol.name()+
					",field_name:"+f.getName());
		}
	}

}

MyColumn.java

package my.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME) //กำหนดว่าใช้เวลา Runtime
@Target({ElementType.FIELD}) //กำหนดว่าใช้กับ Field
public @interface MyColumn {

	String name();
	
}

MyObject.java

package my;

import my.annotation.MyColumn;

public class MyObject {

	@MyColumn(name = "COL_NAME")
	private String name;
	@MyColumn(name = "COL_NICKNAME")
	private String nickname;
	@MyColumn(name = "COL_COLOR")
	private String color;

	public MyObject() {

	}

	public MyObject(String name, String nickname, String color) {
		this.name = name;
		this.nickname = nickname;
		this.color = color;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getNickname() {
		return nickname;
	}

	public void setNickname(String nickname) {
		this.nickname = nickname;
	}

	public String getColor() {
		return color;
	}

	public void setColor(String color) {
		this.color = color;
	}

}