一篇文章带你了解一些Java反射的学习记录

// re.properties

className=com.javalearn.reflect.Cat

methodName=hi

public class Cat {

     private String name = "招财猫" ;

     public void hi() {

         System.out.println( "hi:" + this .name);

     }

}

public class ReflectionDemo {

     public static void main(String[] args) throws Exception {

         // 1.properties对象加载配置文件

         Properties properties = new Properties();

         properties.load( new FileInputStream( "src/main/resources/re.properties" ));

         String className = properties.getProperty( "className" );

         String methodName = properties.getProperty( "methodName" );

         System.out.println( "类名：" + className);

         System.out.println( "方法名：" + methodName);

         // 2.根据类名获取Class类对象

         //  获取Class对象的三种方式：

         //      1.类名.class

         //      2.对象.getClass()

         //      3.Class.forName(类名)

         Class cls = Class.forName(className);

         // 3.生成实例对象

         Object o = cls.newInstance();

         // 4.获取方法

         Method declaredMethod = cls.getDeclaredMethod(methodName);

         // 5.方法.invoke(对象)

         declaredMethod.invoke(o);

         // 6.反射涉及的其他类

         // 6.1Field成员变量

         Field name = cls.getDeclaredField( "name" );

         name.setAccessible( true );   //private属性需暴力反射

         System.out.println(name.get(o));

         // 6.2Constructor构造器

         Constructor constructor = cls.getConstructor(); //方法参数类型与构造器的参数类型一致，不写就是无参构造器

         Object o1 = constructor.newInstance();

         System.out.println(o1);

     }

}

public class PerformanceDemo {

     public static void main(String[] args) throws Exception {

         tradition();

         reflect();

     }

     private static void reflect() throws Exception {

         Class cls = Class.forName( "com.sankuai.yangjin.javalearn.reflect.Cat" );

         Object o = cls.newInstance();

         Method hi = cls.getMethod( "hi" );

         long start = System.currentTimeMillis();

         for ( int i = 0 ; i < 10000 ; i++) {

             hi.invoke(o);

         }

         long end = System.currentTimeMillis();

         System.out.println( "反射耗时：" + (end - start));

     }

     private static void tradition() {

         Cat cat = new Cat();

         long start = System.currentTimeMillis();

         for ( int i = 0 ; i < 10000 ; i++) {

             cat.hi();

         }

         long end = System.currentTimeMillis();

         System.out.println( "传统耗时：" + (end - start));

     }

}

public class LoadDemo {

     public static void main (String[] args) throws Exception {

         Scanner scanner = new Scanner(System.in);

         String num = scanner.next();

         switch (num) {

             case "1" :

                 // 静态加载

                 Dog dog = new Dog();

                 break ;

             case "2" :

                 // 反射,动态加载

                 Class person = Class.forName( "Person" );

                 break ;

             default :

         }

     }

}