反射【框架設(shè)計(jì)的靈魂】：將類的各個(gè)組成部分封裝為其他對(duì)象，這就是反射機(jī)制
好處：1.可以在程序運(yùn)行過程中，操作這些對(duì)象
2.?可以解耦，提高程序的可拓展性
獲取class對(duì)象的3種方式：
1.Class.forname（“全類名”）;將字節(jié)碼文件加載進(jìn)內(nèi)存，返回Class對(duì)象【多用于配置文件，將類名定義在配置文件中。讀取對(duì)象，加載類】
2.類名.class：通過類名的屬性class獲取【多用于參數(shù)的傳遞】
3.對(duì)象.getClass:該方法在object中定義【多用于對(duì)象獲取字節(jié)碼的方式】
同一字節(jié)碼文件（*.class）在一次程序運(yùn)行中，只會(huì)被加載一次，不論通過哪一種 方式獲取到的Class對(duì)象都是同一個(gè)
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Class對(duì)象功能
獲取功能：
1.獲取成員變量們
Field getField(String name)
Field[] getFields() 獲取所有public修飾的成員變量
Field getDeclaredField(String name)
Field[] getDeclaredFields() 獲取所有成員變量
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Field方法
Object get(Object obj) ?【獲取值】
void set(Object obj, Object value) 【設(shè)置傳入對(duì)象值】
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setAccessible（true）【暴力反射】?忽略訪問權(quán)限修飾符的安全檢查
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2.獲取構(gòu)造方法們
Constructor<T> getConstructor(類<?>... parameterTypes)
Constructor?con=personClass.?getConstructor(String.class,int.class)
Constructor<?>[] getConstructors()
Constructor<T> getDeclaredConstructor(類<?>... parameterTypes) ?
Constructor<?>[] getDeclaredConstructors() ?
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Constructor
【創(chuàng)建對(duì)象】
1.T newInstance(Object... initargs) ?
con.newInstance(“張三”，”23”)
2.如果使用空參構(gòu)造方法創(chuàng)建對(duì)象，操作可以簡化：Class對(duì)象的 newInstance方法
personClass.newInstance()
3.獲取成員方法們
Method getMethod(String name, 類<?>... parameterTypes) ??
Method[] getMethods() ?
Method?getDeclaredMethod(String name, 類<?>... parameterTypes)
Method[] getDeclaredMethods()
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Method
執(zhí)行方法
Object invoke(Object obj, Object... args) ?【第一個(gè)參數(shù)是類對(duì)象】
4.獲取全類名
String getName()
返回單位名稱（類，接口，數(shù)組類，原始類型，或無效）的 類對(duì)象表示，作為一個(gè) String。
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創(chuàng)建一個(gè)配置文件pro.properties?
className=cn.itcast.domin.Person
methodName=eat
1.加載配置文件
(1)?創(chuàng)建Properties對(duì)象 ??Properties p= new Properties()；
(2)??加載配置文件，轉(zhuǎn)換為一個(gè)集合 ?
獲取class目錄下的配置文件
ClassLoder classloader=ReflectTest.class.getClassLoader();[獲得該字節(jié)碼文件的類加載器]
IntputSteam is=Classloader.getResourceAsStream(“pro.properties”);[獲取資源所對(duì)應(yīng)的字節(jié)流]
pro.load(i);
2.獲取配置文件中定義的數(shù)據(jù)
String ?className = pro.getProperty(“className”);
String ?className = pro.getProperty(“methodName”);
3.加載該類進(jìn)內(nèi)存
Class ?cls = Class.forName(className);
4.創(chuàng)建對(duì)象
Object obj=cls.newInstance()；
5.獲取方法對(duì)象
Method method=cls.getMethod(methodName);
6.執(zhí)行方法
method.invoke(obj);
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【jvm記載類順序測試】
package edu.xupt.reflect;
public class Demo1 {
static {
System.out.println("main方法將被執(zhí)行");
}
public static void main(String[] args) throws ClassNotFoundException {
System.out.println(Son.z);
}
}
class Father{
static {
System.out.println("父類靜態(tài)代碼塊");
}
public Father() {
System.out.println("父類初始化");
}
static int f=100;
}
class Son extends Father{
static {
System.out.println("子類靜態(tài)代碼塊");
z=200;
}
static int z=100;
static final int N=1000;
public Son() {
System.out.println("子類初始化");
}
}
package edu.xupt.reflect;
public class Demo2 {
public static void main(String[] args) throws ClassNotFoundException {
System.out.println("獲取系統(tǒng)類的加載器");
ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
System.out.println(systemClassLoader);
System.out.println("獲取系統(tǒng)類加載器的父加載器-->拓展加載器");
ClassLoader parent = systemClassLoader.getParent();
System.out.println(parent);
System.out.println("獲取拓展類加載器的父加載器-->根加載器");
ClassLoader parent1 = parent.getParent();
System.out.println(parent1);
System.out.println(Demo2.class.getClassLoader());
Class<?> aClass = Class.forName("edu.xupt.reflect.Demo2");
System.out.println(aClass.getClassLoader());
System.out.println("檢測JDK內(nèi)置類是誰加載的");
System.out.println(Object.class.getClassLoader());
System.out.println(Class.forName("java.lang.ClassLoader" /*Object*/).getClassLoader());
System.out.println("獲得系統(tǒng)類加載器可以加載的路徑");
System.out.println(System.getProperty("java.class.path"));
/*
D:\Java\jdk1.8.0_212\jre\lib\charsets.jar;
D:\Java\jdk1.8.0_212\jre\lib\deploy.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\access-bridge-64.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\cldrdata.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\dnsns.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\jaccess.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\jfxrt.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\localedata.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\nashorn.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\sunec.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\sunjce_provider.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\sunmscapi.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\sunpkcs11.jar;
D:\Java\jdk1.8.0_212\jre\lib\ext\zipfs.jar;
D:\Java\jdk1.8.0_212\jre\lib\javaws.jar;
D:\Java\jdk1.8.0_212\jre\lib\jce.jar;
D:\Java\jdk1.8.0_212\jre\lib\jfr.jar;
D:\Java\jdk1.8.0_212\jre\lib\jfxswt.jar;
D:\Java\jdk1.8.0_212\jre\lib\jsse.jar;
D:\Java\jdk1.8.0_212\jre\lib\management-agent.jar;
D:\Java\jdk1.8.0_212\jre\lib\plugin.jar;
D:\Java\jdk1.8.0_212\jre\lib\resources.jar;
D:\Java\jdk1.8.0_212\jre\lib\rt.jar;
D:\Java\zhang\2019.11.23—注解\out\production\2019.11.23—注解;
D:\IntelliJ IDEA 2019.2.3\lib\idea_rt.jar
*/
}
}
【反射基本方法測試】
package edu.xupt.reflect;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Demo3 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
Class<?> c1 = Class.forName("edu.xupt.reflect.Student");
System.out.println("類名");
System.out.println(c1.getName());
System.out.println(c1.getSimpleName());
System.out.println("======================");
System.out.println("獲得成員變量");
Field[] fields = c1.getFields();
for (Field field : fields) {
System.out.println(field);
}
fields = c1.getDeclaredFields();
for (Field field : fields) {
System.out.println(field);
}
System.out.println("======================");
Method[] methods = c1.getMethods();
for (Method method : methods) {
System.out.println(method);
}
System.out.println(">>>>>>>>>>>>>>>>>>>>");
methods = c1.getDeclaredMethods();
for (Method method : methods) {
System.out.println(method);
}
System.out.println("======================");
Constructor<?> constructor = c1.getConstructor(int.class, String.class, boolean.class);
System.out.println(constructor);
Class<String> stringClass = String.class;
System.out.println(stringClass);
}
}
class Student{
private int id;
private String name;
private boolean sex;
// public String name1;
public Student() {
}
public Student(int id, String name, boolean sex) {
this.id = id;
this.name = name;
this.sex = sex;
}
public Student(int id) {
this.id = id;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public String setName(String name) {
return this.name = name;
}
private void show(){
System.out.println("show被調(diào)用");
}
public void show1(){
System.out.println("show1被調(diào)用");
}
public boolean isSex() {
return sex;
}
public void setSex(boolean sex) {
this.sex = sex;
}
@Override
public String toString() {
return "Student{"
"id=" id
", name='" name '\''
", sex=" sex
'}';
}
}
【單例模式的反射破壞】
package edu.xupt.desidn.singleton;
import java.awt.geom.FlatteningPathIterator;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
public class Demo6 {
public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {
/* test1 test = new test1();
for (int i = 0; i < 100; i ) {
new Thread(test).start();
}*/
Constructor<Singleton6> Constructor = Singleton6.class.getDeclaredConstructor(null);
Constructor.setAccessible(true);
Singleton6 singleton6 = Constructor.newInstance();
Field flag = Singleton6.class.getDeclaredField("flag");
flag.setAccessible(true);
flag.set(singleton6,false);
Singleton6 singleton61 = Constructor.newInstance();
System.out.println(singleton6 == singleton61);
}
}
class Singleton6{
private static boolean flag= false;
private volatile static Singleton6 singleton6;
private Singleton6() {//[可以考慮直接拋異常，不允許進(jìn)構(gòu)造]
if (flag==false){
flag=true;
System.out.println("第一次進(jìn)構(gòu)造");}
else {throw new RuntimeException("不要想著用反射破壞我的單例");
}
}
public static Singleton6 getSingleton6() {
if (singleton6==null){
synchronized (Singleton6.class){
if (singleton6==null){
System.out.println("實(shí)例化");
singleton6 = new Singleton6();
}
}
}
return singleton6;
}
}
class test6 implements Runnable{
@Override
public void run() {
Singleton6.getSingleton6();
}
}
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