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Student???????????

Student?????

???????Student????name?age????????????????????????????????Java???????

????????

• age???????@AgeBound??????????????ageMin?ageMax?????????????????
• name???????@NameBound????????????nameLimit???????????????

public class Student {
    @AgeBound(ageMin = 18, ageMax = 25)
    private int age;
    @NameBound(nameLimit = 5)
    private String name;
    private Student() {
    }
    public Student(int age, String name) {
        this.age = age;
        this.name = name;
    }
    @Override
    public String toString() {
        return "Student{" + 
               "age=" + age + 
               ", name='" + name + '\'' + 
               '}';
    }
}

???????

?????????????@AgeBound?@NameBound???????age?name??????

@AgeBound??

@Target(ElementType.TYPE, ElementType.CONSTRUCTOR, ElementType.FIELD, ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@interface AgeBound {
    int ageMin();
    int ageMax();
}

@NameBound??

@Target(ElementType.TYPE, ElementType.CONSTRUCTOR, ElementType.FIELD, ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@interface NameBound {
    int nameLimit();
}

?????

????????????????????????StudentFactory????????????????????????????

???????

public class StudentFactory {
    private Class studentCls = Student.class;
    public Student getStudent(int age, String name) 
            throws NoSuchMethodException, IllegalAccessException, 
           InvocationTargetException, InstantiationException, NoSuchFieldException {
        // ????
        judgeAge(age);
        // ??????
        judgeName(name);
        // ??????Student??
        Constructor declaredConstructor = 
                studentCls.getDeclaredConstructor(int.class, String.class);
        declaredConstructor.setAccessible(true);
        Student student = (Student) declaredConstructor.newInstance(age, name);
        return student;
    }
    private void judgeName(String name) 
            throws NoSuchFieldException {
        Field nameField = studentCls.getDeclaredField("name");
        if (nameField.isAnnotationPresent(NameBound.class)) {
            NameBound nameBound = nameField.getAnnotation(NameBound.class);
            int nameLimit = nameBound.nameLimit();
            if (name.length() > nameLimit) {
                throw new IllegalArgumentException("?????,????" + name.length());
            }
        }
    }
    private void judgeAge(int age) 
            throws NoSuchFieldException {
        Field ageField = studentCls.getDeclaredField("age");
        if (ageField.isAnnotationPresent(AgeBound.class)) {
            AgeBound ageBound = ageField.getAnnotation(AgeBound.class);
            int ageMax = ageBound.ageMax();
            int ageMin = ageBound.ageMin();
            if (age < ageMin || age > ageMax) {
                throw new IllegalArgumentException("????? :" + age);
            }
        }
    }
}

????

??????Test???????????

import java.lang.reflect.InvocationTargetException;
public class Test {
    public static void main(String[] args) 
            throws InvocationTargetException, NoSuchMethodException, 
           NoSuchFieldException, InstantiationException, IllegalAccessException {
        // ????????
        Student student = new StudentFactory().getStudent(20, "??");
        System.out.println(student);
        // ?????????
        try {
            Student student1 = new StudentFactory().getStudent(100, "??3333");
            System.out.println(student1);
        } catch (Exception e) {
            System.out.println("?????" + e.getMessage());
        }
    }
}

????

• ???????????Student??????
• ??????????????????? IllegalArgumentException???????????

????????????Student???????????????????????????????????