Java中反射

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類載入的三種機制1、通過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");

對象比較

//比較記憶體位址，類載入器只會建立一次System.out.println(c==c2); //比較的是屬性值System.out.println(c.equals(c2));

反射

其實就是把class檔案進行結構拆解：

1. 建構函式（有參/無參）
2. 成員變數（屬性）
3. 方法

反射建構函式

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

暴力反射（不建議使用，破壞了封裝性、安全性）

//建構函式是私人的 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，取消運行時許可權檢查constructor.setAccessible(true);Object obj=constructor.newInstance("dd",22);System.out.println(obj);

動態調用內部方法

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

擷取所有成員變數

Class c = Class.forName("tianpo.com.demo.People");# 擷取所有public類型的成員變數Field[] fs=c.getFields();# 擷取所有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();//動態賦值field.set(obj1,18);System.out.println(obj1);

反射的泛型擦除

ArrayList<String> array = new ArrayList<String>();array.add("張三");// 編譯時間會做類型檢查//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);

通過配置執行調用建立一個config.properties

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

反射調用

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);

Java中反射