类 Class 的实例代表运行时java应用程序中的类和接口。枚举类型是一种类，注解类是一种接口。数组是共享同一种类的。基本类型（boolean、byte、char、short、int、long、float和double）和关键字void也表示为类对象。Class 没有公开的构造方法，只能由JVM创建。 当类加载器调用defineClass方法并传递类文件字节给jvm，jvm会自动构建Class 对象。

1. java.io.Serializable2. GenericDeclaration  GenericDeclaration 所有声明泛型变量的实体要实现此接口（注：后续会在“我看JAVA 之 泛型“阐述）  唯一的方法：  public TypeVariable<?>[] getTypeParameters();//获取当前“实体”上声明的“泛型变量"。3. Type   Type是java语言中所有类型的公共高级接口，它们包括原始类型、参数化类型、数组类型、泛型变量和基本类型。  默认方法：  default String getTypeName() {      return toString();  }
4. AnnotatedElement  java.lang.reflect.AnnotatedElement 接口定义了获取在当前JVM中运行程序的注解元素。这个接口允许通过反射的方式获取注解。通过当前接口方法获取到的注解都是不可变且序列化的。

      public static Class<?> forName(String className)                  throws ClassNotFoundException {          Class<?> caller = Reflection.getCallerClass();          return forName0(className, true, ClassLoader.getClassLoader(caller), caller);      }
      @CallerSensitive      public static Class<?> forName(String name, boolean initialize,                                     ClassLoader loader)          throws ClassNotFoundException      {          Class<?> caller = null;          SecurityManager sm = System.getSecurityManager();          if (sm != null) {              // Reflective call to get caller class is only needed if a security manager              // is present.  Avoid the overhead of making this call otherwise.              caller = Reflection.getCallerClass();              if (loader == null) {                  ClassLoader ccl = ClassLoader.getClassLoader(caller);                  if (ccl != null) {                      sm.checkPermission(                          SecurityConstants.GET_CLASSLOADER_PERMISSION);                  }              }          }          return forName0(name, initialize, loader, caller);      }
      /** Called after security check for system loader access checks have been made. */      private static native Class<?> forName0(String name, boolean initialize,                                              ClassLoader loader,                                              Class<?> caller)          throws ClassNotFoundException;

1. Integer.class2. new Integer(1).getClass()3. Class.forName("java.lang.Integer")

    package chapter03;
  import java.lang.annotation.ElementType;  import java.lang.reflect.InvocationTargetException;
  public class TestClass {
      public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
          System.out.println("--- 3 mode get obj's Class ---");          System.out.println(Integer.class);          System.out.println(Integer.valueOf(1).getClass());          System.out.println(Class.forName("java.lang.Integer"));          System.out.println(int.class);          System.out.println("int is privitive type or not ? " + int.class.isPrimitive());
          // array          System.out.println("--- array' Class ---");          System.out.println(new Integer[]{1, 3, 5}.getClass());          System.out.println(new Object[]{1, 3, 5}.getClass());          System.out.println(new Integer[][]{{1, 2, 3}, {2, 3, 4}, {3, 4, 5}}.getClass());
          // void package          System.out.println("--- void & package' Class ---");          System.out.println(Void.class);          System.out.println(void.class);          System.out.println(Package.class);
          // enum          System.out.println("--- enum' Class ---");          System.out.println(ElementType.class);          System.out.println("ElementType is enum or not ? " + ElementType.class.isEnum());
          // annotation          System.out.println("--- annotation' Class ---");          System.out.println(Deprecated.class);          System.out.println("Deprecated is interface or not ? " + Deprecated.class.isInterface());          System.out.println("Deprecated is annotation or not ? " + Deprecated.class.isAnnotation());
          // class' Class          System.out.println("--- class' Class ---");          System.out.println(Class.forName("java.lang.Integer").getClass());
          // module          System.out.println(Class.forName("chapter03.Test").getModule());
          //new instance          System.out.println(Class.forName("chapter03.Test").getDeclaredConstructor());          Class.forName("chapter03.Test").getDeclaredConstructor().newInstance();          Class.forName("chapter03.Test").newInstance();
      }  }
  class Test {      private Test() {
      }  }