Java反射2

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3.2、Constructor类用于创建对象的方法

• 方法介绍

  方法名	说明
  T newInstance(Object...initargs)	根据指定的构造方法创建对象
  setAccessible(boolean flag)	设置为true,表示取消访问检查

• 示例代码

  // Student类同上一个示例,这里就不在重复提供了
  public class ReflectDemo2 {
      public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
          //T newInstance(Object... initargs)：根据指定的构造方法创建对象
          //method1();
          //method2();
          //method3();
          //method4();
  
      }
  
      private static void method4() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
          //获取一个私有的构造方法并创建对象
          //1.获取class对象
          Class clazz = Class.forName("com.itheima.myreflect3.Student");
  
          //2.获取一个私有化的构造方法.
          Constructor constructor = clazz.getDeclaredConstructor(String.class);
  
          //被private修饰的成员,不能直接使用的
          //如果用反射强行获取并使用,需要临时取消访问检查
          constructor.setAccessible(true);
  
          //3.直接创建对象
          Student student = (Student) constructor.newInstance("zhangsan");
  
          System.out.println(student);
      }
  
      private static void method3() throws ClassNotFoundException, InstantiationException, IllegalAccessException {
          //简写格式
          //1.获取class对象
          Class clazz = Class.forName("com.itheima.myreflect3.Student");
  
          //2.在Class类中,有一个newInstance方法,可以利用空参直接创建一个对象
          Student student = (Student) clazz.newInstance();//这个方法现在已经过时了,了解一下
  
          System.out.println(student);
      }
  
      private static void method2() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
          //1.获取class对象
          Class clazz = Class.forName("com.itheima.myreflect3.Student");
  
          //2.获取构造方法对象
          Constructor constructor = clazz.getConstructor();
  
          //3.利用空参来创建Student的对象
          Student student = (Student) constructor.newInstance();
  
          System.out.println(student);
      }
  
      private static void method1() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
          //1.获取class对象
          Class clazz = Class.forName("com.itheima.myreflect3.Student");
  
          //2.获取构造方法对象
          Constructor constructor = clazz.getConstructor(String.class, int.class);
  
          //3.利用newInstance创建Student的对象
          Student student = (Student) constructor.newInstance("zhangsan", 23);
  
          System.out.println(student);
      }
  }
  

3.3、小结

• 获取class对象

  三种方式: Class.forName(“全类名”), 类名.class, 对象名.getClass()

• 获取里面的构造方法对象

  getConstructor (Class... parameterTypes) getDeclaredConstructor (Class... parameterTypes)

• 如果是public的，直接创建对象

  newInstance(Object... initargs)

• 如果是非public的，需要临时取消检查，然后再创建对象

  setAccessible(boolean) 暴力反射