Reflection in Java

Three kinds of mechanisms for class loading 1, by GetClass

People p =new People();Class c = p.getClass();

2, People.class

Class c1=People.class;

3, Class.forName ("Tianpo.com.demo.People");

Class c2=Class.forName("tianpo.com.demo.People");

Object comparison

//比较内存地址，类加载器只会创建一次System.out.println(c==c2); //比较的是属性值System.out.println(c.equals(c2));

Reflection

In fact, the class file is structured to disassemble:

1. Constructors (with/without parameters)
2. Member variables (properties)
3. Method

Reflection constructors

Class c =Class.forName("tianpo.com.demo.People");## 有参Constructor constructor=c.getConstructor(String.class,int.class);## 无参Constructor constructor1=c.getConstructor();Object obj=constructor.newInstance("dd",22);People p =(People)obj;System.out.println(p);

Violent reflexes (not recommended, damaging encapsulation, security)

//构造函数是私有的 private People(String name, int age) {    super();    this.name = name;    this.age = age;}Class c =Class.forName("tianpo.com.demo.People");Constructor constructor=c.getDeclaredConstructor(String.class,int.class);//暴力反射，取消运行时权限检查constructor.setAccessible(true);Object obj=constructor.newInstance("dd",22);System.out.println(obj);

Dynamic invocation of internal methods

Class c = Class.forName("tianpo.com.demo.People");Constructor con = c.getConstructor();Method m =c.getMethod("eat");Object obj1=con.newInstance();m.invoke(obj1);

Get all member variables

Class c = Class.forName("tianpo.com.demo.People");# 获取所有public类型的成员变量Field[] fs=c.getFields();# 获取所有privateField[] fs1=c.getDeclaredFields();for(Field field:fs){    System.out.println(field);}Field field=c.getDeclaredField("age");Constructor con = c.getConstructor();Method m =c.getMethod("eat");Object obj1=con.newInstance();//动态赋值field.set(obj1,18);System.out.println(obj1);

Reflection-based generic erase

ArrayList<String> array = new ArrayList<String>();array.add("张三");// 编译时会做类型检查//array.add(10);Class c = array.getClass();Method m = c.getMethod("add",Object.class);m.invoke(array,10);m.invoke(array,13.8);System.out.println(array);

Create a config.properties by configuring the Execute call

className = tianpo.com.demo.PeoplemethodName = eatclassName = tianpo.com.demo.StudentmethodName = StudyclassName = tianpo.com.demo.WorkermethodName = Work

Reflection Call

FileReader rd = new FileReader("config.properties");Properties pro = new Properties();pro.load(rd);rd.close();String className = pro.getProperty("className");String methodName = pro.getProperty("methodName");Class c =Class.forName(className);Method m = c.getMethod(methodName);Object obj=c.newInstance();m.invoke(obj);

Reflection in Java