Annotation_demo

参考：https://zhuanlan.zhihu.com/p/60730622

CheckAge.java

package com.hmb;

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

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface CheckAge {
    int min() default 0;
    int max() default 100;
}

InitSex.java

package com.hmb;

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

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface InitSex {
    enum SEX_TYPE { MAN, WOMAN};
    SEX_TYPE sex() default SEX_TYPE.MAN;
}

People.java

package com.hmb;

public class People {
    @CheckAge()
    private int age;

    @InitSex()
    private String sex;

    public People(int age, String sex) {
        this.age = age;
        this.sex = sex;
    }

    public People() {
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }
}

Children.java

package com.hmb;

public class Children extends People {
    @CheckAge(max = 18)
    private int age;

    public void setAge(int age) {
        this.age = age;
    }
}

Main.java

package com.hmb;

import java.lang.reflect.Field;

public class Main {
    static void initSex(People people) {
        Field[] fields = People.class.getDeclaredFields();
        for (Field field : fields) {
            if (field.isAnnotationPresent(InitSex.class)) {
                InitSex sex = field.getAnnotation(InitSex.class);
                try {
                    field.setAccessible(true);
                    field.set(people, sex.sex().toString());
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
                System.out.println("finished init sex");
            }
        }
    }

    static boolean checkAge(People people) {
        Field[] fields = People.class.getDeclaredFields();
        for (Field field : fields) {
            if (field.isAnnotationPresent(CheckAge.class)) {
                CheckAge checkAge = field.getAnnotation(CheckAge.class);
                try {
                    field.setAccessible(true);
                    int age = (int) field.get(people);
                    if (age < checkAge.min() || age > checkAge.max()) {
                        return false;
                    }
                    return true;
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }

        return false;
    }

    public static void main(String[] args) {
        People people = new People();
        System.out.println(people.getSex());
        initSex(people);
        System.out.println(people.getSex());

        people.setAge(-1);
        System.out.println(checkAge(people));
        people.setAge(101);
        System.out.println(checkAge(people));
        people.setAge(20);
        System.out.println(checkAge(people));

        System.out.println("==============");

        Children children = new Children();
        children.setAge(-1);
        System.out.println(checkAge(children));
        children.setAge(19);
        System.out.println(checkAge(children));
        children.setAge(7);
        System.out.println(checkAge(children));
    }
}