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测试代码:
Test test=new Test();
      Class c1=test.getClass();
      //获取所有构造方法
      //Constructor[] declaredConstructors = c1.getDeclaredConstructors();
      //获取所有public构造方法
      Constructor[] declaredConstructors = c1.getConstructors();
      for (int i = 0; i < declaredConstructors.length; i++) {
         System.out.print(Modifier.toString(declaredConstructors[i].getModifiers())+"参数: ");
         //获取构造方法的所有参数类型
         Class[] parameterTypes = declaredConstructors[i].getParameterTypes();
         for (int j = 0; j < parameterTypes.length; j++) {
            System.out.print(parameterTypes[j].getName()+" ");
         }
         System.out.println();
      }
      System.out.println("==========================");
      try {
//       Constructor declaredConstructor = c1.getDeclaredConstructor(int.class,String.class);
//       Object zhangsan = declaredConstructor.newInstance(24, "张三");
         Constructor declaredConstructor = c1.getDeclaredConstructor(String.class);
         declaredConstructor.setAccessible(true);
         Object zhangsan = declaredConstructor.newInstance("张三");
         Method method = c1.getDeclaredMethod("wel", String.class);
         method.setAccessible(true);
         method.invoke(zhangsan,"哈喽，朋友");
         Field field = c1.getDeclaredField("name");
         field.setAccessible(true);
         field.set(zhangsan,"jjt");
         System.out.println(field.get(zhangsan).toString());
         System.out.print(Modifier.toString(declaredConstructor.getModifiers())+":");
         Class[] parameterTypes = declaredConstructor.getParameterTypes();
         for (int i = 0; i < parameterTypes.length; i++) {
            System.out.print(parameterTypes[i].getName()+" ");
         }
         System.out.println();
      } catch (NoSuchMethodException e) {
         e.printStackTrace();
      } catch (IllegalAccessException e) {
         e.printStackTrace();
      } catch (InstantiationException e) {
         e.printStackTrace();
      } catch (InvocationTargetException e) {
         e.printStackTrace();
      } catch (NoSuchFieldException e) {
         e.printStackTrace();
      }

class Test{
   private int age;
   private String name;
   private int testint;

   public Test(int age) {
      this.age = age;
   }

   public Test(int age, String name) {
      this.age = age;
      this.name = name;
      System.out.println(name+"的年龄:"+age);
   }

   private Test(String name) {
      this.name = name;
      System.out.println("name = " + name);
   }

   public Test() {
   }

   private void wel(String a){
      System.out.println("a = " + a);
   }
}