java反射和注解

反射

获取class对象的三种方法

①：Class.forName("全类名");
②：类名.class
③：对象.getclass();

代码样例

java">package com.ithema;public class Main {public static void main(String[] args) throws ClassNotFoundException {//第一种方式//最为常用Class aClass1 = Class.forName("com.ithema.student");System.out.println(aClass1);//第二种方式//一般更多作为参数传递传递Class aClass2 = student.class;System.out.println(aClass2);//第三种方式//当有了这个类的对象时才可以使用student s=new student();Class aClass3 = s.getClass();System.out.println(aClass3);}
}

利用反射获取构造方法

代码样例

java">package ithema;import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Parameter;public class Main {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {//1.获取字节码文件对象Class aClass1 = Class.forName("ithema.student");//2.获取构造方法//获取public修饰的构造方法
//        Constructor[] cons = aClass1.getConstructors();
//        for (Constructor con : cons) {
//            System.out.println(con);
//        }//获取所有的构造方法
//        Constructor[] cons2 = aClass1.getDeclaredConstructors();
//        for (Constructor con : cons2) {
//            System.out.println(con);
//        }//获取单个的构造方法
//        Constructor con1 = aClass1.getDeclaredConstructor();
//        System.out.println(con1);
//
//        Constructor con2 = aClass1.getDeclaredConstructor(String.class);
//        System.out.println(con2);
//
//        Constructor con3 = aClass1.getDeclaredConstructor(int.class);
//        System.out.println(con3);Constructor con4 = aClass1.getDeclaredConstructor(String.class, int.class);System.out.println(con4);//获得权限修饰符int modifiers = con4.getModifiers();System.out.println(modifiers);//得到构造方法所有的参数类型Parameter[] parameters = con4.getParameters();for (Parameter parameter : parameters) {System.out.println(parameter);}//通过反射得到的构造方法创建对象//暴力反射：临时取消权限校验con4.setAccessible(true);student stu = (student) con4.newInstance("张三", 23);System.out.println(stu);}
}

里面的学生类对象代码：

java">package ithema;public class student {String name;int age;public student() {}public student(String name) {this.name = name;}protected student(int age) {this.age = age;}private student(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}
}

利用反射获取成员变量

代码样例

java">package adsads;import java.lang.reflect.Field;public class Main {public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {//第一种方式//最为常用Class aClass1 = Class.forName("adsads.student");//获取所有成员变量
//        Field[] fields = aClass1.getDeclaredFields();
//        for (Field field : fields) {
//            System.out.println(field);
//        }//获取单个成员变量Field name = aClass1.getDeclaredField("name");System.out.println(name);//获取权限修饰符int modifiers = name.getModifiers();System.out.println(modifiers);//获取成员变量的名字String n=name.getName();System.out.println(n);//获取成员变量的数据类型Class<?> type = name.getType();System.out.println(type);//获取成员变量记录的值student s=new student("张三",32,"男");name.setAccessible(true);String value =(String) name.get(s);System.out.println(value);//修改对象里面记录的值name.set(s,"list");System.out.println(s);}
}

里面的学生类对象代码：

java">package adsads;public class student {private String name;private int age;public String gender;public student() {}public student(String name, int age, String gender) {this.name = name;this.age = age;this.gender = gender;}@Overridepublic String toString() {return "student{" +"name='" + name + '\'' +", age=" + age +", gender='" + gender + '\'' +'}';}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}
}

利用反射获取成员方法

java">package ads;import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;public class Main {public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException, NoSuchMethodException, InvocationTargetException {//第一种方式//最为常用Class aClass1 = Class.forName("ads.student");//获取里面所有的方法对象(包含父类公共的)
//        Method[] methods = aClass1.getMethods();
//        for (Method method : methods) {
//            System.out.println(method);
//        }//获取里面所有的方法对象(不包含父类,但是可以获取本类中私有的)
//        Method[] methods1 = aClass1.getDeclaredMethods();
//        for (Method method : methods1) {
//            System.out.println(method);
//        }//获取指定的单一方法Method m = aClass1.getDeclaredMethod("eat", String.class);System.out.println(m);//获取方法的修饰符int modifiers = m.getModifiers();System.out.println(modifiers);//获取方法的名字String name = m.getName();System.out.println(name);//获取方法的形参Parameter[] parameters = m.getParameters();for (Parameter parameter : parameters) {System.out.println(parameter);}//获取方法抛出的异常Class[] exceptionTypes = m.getExceptionTypes();for (Class exceptionType : exceptionTypes) {System.out.println(exceptionType);}//方法运行student s=new student();m.setAccessible(true);//参数1：s 表示方法的调用者//参数2：汉堡包 表示调用方法的时候传递的实际参数m.invoke(s,"汉堡包");}
}

里面的学生类对象代码：

java">package ads;import java.io.IOException;public class student {private String name;private int age;public student() {}public student(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public void sleep(){System.out.println("睡觉");}private void eat(String something)throws IOException ,NullPointerException{System.out.println("在吃"+something);}
}

反射的作用