JAVA学习日记（二十七）反射

一、反射的概述

二、获取Class对象的三种方式

import testpackage.Student;public class Main {public static void main(String[] args) throws ClassNotFoundException {//获取.class对象的三种方式//1. Class.forName("全类名")//2. 类名.class//3. 对象.getClass()//方法一//全类名：包名+类名//最常用Class clazz = Class.forName("testpackage.Student");System.out.println(clazz); //class testpackage.Student//方法二//一般更多当做参数进行传递Class clazz2= Student.class;System.out.println(clazz==clazz2);  //true//方法三//当已经存在这个类的对象时，才可以使用Student stu=new Student();Class clazz3=stu.getClass();System.out.println(clazz3==clazz); //true}
}

Student类：

package testpackage;import java.io.IOException;public class Student {private String name;private String area;public String testfield;private int age;public Student() {}public Student(String name, String area, int age) {this.name = name;this.area = area;this.age = age;}private Student(String name){this.name=name;}/*** 获取* @return name*/public String getName() {return name;}/*** 设置* @param name*/public void setName(String name) {this.name = name;}/*** 获取* @return area*/public String getArea() {return area;}/*** 设置* @param area*/public void setArea(String area) {this.area = area;}/*** 获取* @return age*/public int getAge() {return age;}/*** 设置* @param age*/public void setAge(int age) {this.age = age;}public String toString() {return "Student";}public void eat(String something) throws IOException,NullPointerException {System.out.println("在吃"+something);}public void eat(int number){System.out.println("吃了"+number+"个东西");}
}

三、利用反射获取构造方法

import testpackage.Student;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Parameter;public class Reflect_construction {public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {//获取Class类中的构造方法//1.获取Class字节码文件对象Class clazz= Student.class;//2.获取构造方法（公共）Constructor cons = clazz.getConstructor(); //不传递参数，则获取空参构造方法System.out.println(cons); //public testpackage.Student()System.out.println("___________________________________________");Constructor[] cons2 = clazz.getConstructors();for (Constructor constructor : cons2) {System.out.println(constructor);}//public testpackage.Student()//public testpackage.Student(java.lang.String,java.lang.String,int)System.out.println("___________________________________________");//获取全部构造方法Constructor[] cons3 = clazz.getDeclaredConstructors();for (Constructor c : cons3) {System.out.println(c);}//public testpackage.Student()//public testpackage.Student(java.lang.String,java.lang.String,int)//private testpackage.Student(java.lang.String)System.out.println("___________________________________________");//获取带参私有构造方法Constructor cons4 = clazz.getDeclaredConstructor(String.class);System.out.println(cons4);//private testpackage.Student(java.lang.String)System.out.println("___________________________________________");//获取带参公共构造方法Constructor cons5 = clazz.getDeclaredConstructor(String.class, String.class, int.class);System.out.println(cons5);//public testpackage.Student(java.lang.String,java.lang.String,int)System.out.println("___________________________________________");//获取构造方法的权限修饰符System.out.println(cons5.getModifiers()); //1  --  publicSystem.out.println(cons4.getModifiers()); //2  --  privateSystem.out.println("___________________________________________");//获取构造方法里的参数Parameter[] parameters = cons5.getParameters();for (Parameter parameter : parameters) {System.out.println(parameter);}//java.lang.String arg0//java.lang.String arg1//int arg2System.out.println("___________________________________________");//使用反射创建对象（不可以直接用newInstance方法来调用私有化的构造方法）Student stu = (Student)cons5.newInstance("张三", "李四", 18);System.out.println(stu);//Student{name = 张三, area = 李四, age = 18}//调用私有化方法创建对象cons4.setAccessible(true); //表示临时取消权限校验Student stu1 =(Student) cons4.newInstance("张三");System.out.println(stu1);//Student{name = 张三, area = null, age = 0}}
}

四、利用反射获取成员变量及功能

import testpackage.Student;import java.lang.reflect.Field;public class Reflect_Field {public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {//利用反射获取成员变量Class clazz = Class.forName("testpackage.Student");//获取全部公共成员变量Field[] fields = clazz.getFields();for (Field field : fields) {System.out.println(field);}//public java.lang.String testpackage.Student.testfieldSystem.out.println("-----------------------------");//获取全部成员变量Field[] declaredFields = clazz.getDeclaredFields();for (Field declaredField : declaredFields) {System.out.println(declaredField);}//private java.lang.String testpackage.Student.name//private java.lang.String testpackage.Student.area//public java.lang.String testpackage.Student.testfield//private int testpackage.Student.ageSystem.out.println("-----------------------------");//获取单个成员变量(参数为变量的名称)Field name = clazz.getDeclaredField("name");System.out.println(name);//private java.lang.String testpackage.Student.nameSystem.out.println("-----------------------------");//获取成员变量的修饰符int modifiers = name.getModifiers();System.out.println(modifiers); //2  -- privateSystem.out.println("-----------------------------");//获取成员变量的名称String n=name.getName();System.out.println(n);//nameSystem.out.println("-----------------------------");//获取成员变量的类型Class<?> type = name.getType();System.out.println(type);//class java.lang.StringSystem.out.println("-----------------------------");//获取成员变量记录的值(私有,需临时取消权限检验)name.setAccessible(true);Student stu=new Student("张三","南京",19);Object o = name.get(stu);System.out.println(o); //张三System.out.println("-----------------------------");//修改对象里面记录的值name.set(stu,"啊实打实");System.out.println(stu);//Student{name = 啊实打实, area = 南京, age = 19}}
}

五、利用反射获取成员方法

import testpackage.Student;import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.sql.SQLOutput;public class Reflect_Method {public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {//利用反射获取成员方法Class clazz = Student.class;//获取类中所有的方法对象（包含父类中所有的公共方法）Method[] methods = clazz.getMethods();for (Method method : methods) {System.out.println(method);}//public java.lang.String testpackage.Student.getName()//public java.lang.String testpackage.Student.toString()//public void testpackage.Student.setName(java.lang.String)//public java.lang.String testpackage.Student.getArea()//public int testpackage.Student.getAge()//public void testpackage.Student.setAge(int)//public void testpackage.Student.setArea(java.lang.String)//public boolean java.lang.Object.equals(java.lang.Object)//public native int java.lang.Object.hashCode()//public final native java.lang.Class java.lang.Object.getClass()//public final native void java.lang.Object.notify()//public final native void java.lang.Object.notifyAll()//public final void java.lang.Object.wait(long) throws java.lang.InterruptedException//public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException//public final void java.lang.Object.wait() throws java.lang.InterruptedExceptionSystem.out.println("____________________________________");//获取类中所有的方法对象（不能获取父类的，但是可以获取本类中的私有方法）Method[] declaredMethods = clazz.getDeclaredMethods();for (Method declaredMethod : declaredMethods) {System.out.println(declaredMethod);}//public void testpackage.Student.setArea(java.lang.String)//public java.lang.String testpackage.Student.getArea()//public void testpackage.Student.setAge(int)//public int testpackage.Student.getAge()//public java.lang.String testpackage.Student.getName()//public java.lang.String testpackage.Student.toString()//public void testpackage.Student.setName(java.lang.String)System.out.println("____________________________________");//获取类中指定的单一方法 （参数为 方法名,方法传递的参数类型）Method eat1 = clazz.getDeclaredMethod("eat", String.class);System.out.println(eat1);Method eat2 = clazz.getDeclaredMethod("eat", int.class);System.out.println(eat2);//public void testpackage.Student.eat(java.lang.String)//public void testpackage.Student.eat(int)System.out.println("____________________________________");//获取方法名字  获取方法形参 获取方法修饰符String name=eat1.getName();System.out.println(name);//eatParameter[] parameters = eat1.getParameters();for (Parameter parameter : parameters) {System.out.println(parameter);}//java.lang.String arg0int modifiers = eat1.getModifiers();System.out.println(modifiers); //1 -- publicSystem.out.println("____________________________________");//获取方法抛出的异常Class[] exceptionTypes = eat1.getExceptionTypes();for (Class exceptionType : exceptionTypes) {System.out.println(exceptionType);}//class java.io.IOException//class java.lang.NullPointerExceptionSystem.out.println("____________________________________");//方法运行/*Method类中用于创建对象的方法Object invoke(Object obj,Object...args) ： 运行方法参数一：用obj对象调用方法参数二：调用方法的传递的参数（如果没有就不写）返回值：方法的返回值（如果没有不写）*///同样如果调用的是private修饰的私有方法，则需要临时取消权限检验Student stu=new Student();eat1.invoke(stu,"汉堡包");//  在吃汉堡包}
}

 六、反射的作用