// Type.class로 접근하는 방법
Class<Book> bookClass = Book.class;

// 인스턴스로 접근하는 방법
Book book = new Book();
Class<? extends Book> aClass = book.getClass();

// 클래스 문자열로 읽어오는 방법 클래스가 없다면 ClassNotFoundException발생
Class<?> aClass1 = Class.forName("me.mkhwang.Book");

// Type.class로 접근하는 방법
Class<Book> bookClass = Book.class;
// 인스턴스로 접근하는 방법
Book book = new Book();

Arrays.stream(bookClass.getDeclaredFields()).forEach(f -> {
    try {
        f.setAccessible(true); //접근제어자 무시
        int modifiers = f.getModifiers();
        System.out.printf("%s %s %s %s \n", 
                f, f.get(book), Modifier.isPrivate(modifiers), Modifier.isStatic(modifiers));
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
});

//메서드
Arrays.stream(bookClass.getMethods()).forEach(System.out::println);

//생성자
Arrays.stream(bookClass.getDeclaredConstructors()).forEach(System.out::println);

//상속
System.out.println(bookClass.getSuperclass());

//인터페이스
Arrays.stream(bookClass.getInterfaces()).forEach(System.out::println);

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD})
@Inherited
public @interface MyAnnotation {
}

Class<?> bookClass = Class.forName("me.mkhwang.Book");
Constructor<?> constructor = bookClass.getConstructor(String.class);
Book book = (Book) constructor.newInstance("myBook");
System.out.println(book);

//필드 값 변경
Field b = Book.class.getDeclaredField("B");
System.out.println(b.get(book));
b.set(book, "BBBBB");
System.out.println(b.get(book));

//invoke가 해당 메소드 실행
Method c = Book.class.getDeclaredMethod("c");
Object invoke = c.invoke(book);

//method에 parameter가 있는경우 type도 넣어준다 primitive / reference type체크 함.
Method d = Book.class.getDeclaredMethod("sum", int.class, int.class);
Object invoke1 = d.invoke(book, 1, 2);
System.out.println(invoke1);

public static <T> T getObject(Class<T> classType){
    T instance = createInstance(classType);
    Arrays.stream(classType.getDeclaredFields()).forEach(f -> {

        if (f.getAnnotation(Inject.class) != null){
            Object fieldInstance = createInstance(f.getType());
            f.setAccessible(true);
            try {
                f.set(instance, fieldInstance);
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            }
        }

    });
    return instance;
}

private static <T> T createInstance(Class<T> classType) {
    try {
        return classType.getConstructor(null).newInstance();
    } catch (InstantiationException | NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
        throw new RuntimeException(e);
    }
}