反射(獲取構造器、方法)

反射

 

反射: 1.獲取class對象 方式1: Class clazz=Class.forName("全限定名") 方式2: Class clazz=類名.class; 方式3: Class clazz=對象.getClass;  

 

  2.可以獲取對應類的構造方法(了解) Constructor con = clazz.getConstructor(Class .. paramClass); Person p = (Person) con.newInstance(參數);

　　 persion.java

package com.reflect; public class Persion { private Integer id; private String username; private String password; public Persion() { System.out.println("無參構造器"); } public Persion(Integer id, String username, String password) { this.id = id; this.username = username; this.password = password; System.out.println("帶參構造器"); } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } }

　　text01.java

package com.reflect; import org.junit.Test; import java.lang.reflect.*; public class test01 { @Test public void run() throws Exception { //獲取class對象
        Class clazz = Class.forName("com.reflect.Persion"); //獲取無參構造器
        Constructor con1  = clazz.getConstructor(); Persion p1 = (Persion) con1.newInstance(); //獲取帶參構造器
        Constructor con2 = clazz.getConstructor(Integer.class,String.class,String.class); Persion p2 = (Persion) con2.newInstance(1,"hjh","12345"); } }

 

 3.可以通過clazz創建一個對象(了解) clazz.newInstance();//相當於調用的無參構造器
    4.可以通過clazz獲取所有的字段 getFiled()(了解中的了解)

 

 5.可以通過clazz獲取所有的方法 Method m = clazz.getMethod("sleep");//獲取公共的方法
        Method m = clazz.getDeclaredMethod("sleep");//獲取任意的方法
 注意:若是私有的方法 必須讓該方法可以訪問 m.setAccessible(true);

　　 persion.java

package com.reflect; public class Persion { private Integer id; private String username; private String password; public Persion() { System.out.println("無參構造器"); } public Persion(Integer id, String username, String password) { this.id = id; this.username = username; this.password = password; System.out.println("帶參構造器"); } public Persion( String username) { this.username = username; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public void sport() { System.out.println("游泳"); } public void sport(String username) { System.out.println(username+"在游泳"); } private void sleep() { System.out.println("睡覺"); } private String sleep(String username) { return username+"在睡覺"; } }

　　test02.java

package com.reflect; import org.junit.Test; import java.lang.reflect.*; public class test02 { @Test public void run() throws Exception { //獲取class對象
        Class clazz = Persion.class; //獲取public修飾的方法
        Method m1 = clazz.getMethod("sport"); m1.invoke(clazz.newInstance()); //獲取任意方法
        Method m2 = clazz.getDeclaredMethod("sleep"); //授權給私有和受保護方法，使之可以被訪問
        m2.setAccessible(true); //執行方法
 m2.invoke(clazz.newInstance()); //執行有返回值的方法 
        Method m3 = clazz.getDeclaredMethod("sleep",String.class); //授權給私有和受保護方法，使之可以被訪問
        m3.setAccessible(true); String str = (String) m3.invoke(clazz.newInstance(),"hjh"); System.out.println(str); } }

 

6.Method對象的invoke是有返回值,他的返回值就是目標方法執行的返回值 總結: 有了class對象之后,無所不能.