1.反射機制

1.什麼是反射？

就是正在運行，動態獲取這個類的全部信息、

 

2.反射機制的做用

1.反編譯： .class->.java

2.經過反射機制訪問java對象的屬性，方法，構造器方法等。

 

 

運用

 

package com.jlong.classfrorm;

 

import com.jlong.entity.User;

 

import java.lang.reflect.Field;

import java.lang.reflect.InvocationTargetException;

 

public class ClassFrorm {

    public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException, NoSuchFieldException {

        Class<?> forName = Class.forName("com.jlong.entity.User");

      /*  Object o = aClass.newInstance();

        User user = (User) o;

        System.out.println(user.toString());*/

        //有參構造器初始化變量

      /*  Constructor<?> constructor = aClass.getConstructor(String.class);

        Object jlong = constructor.newInstance("jlong");

        User user = (User) jlong;

        String name = user.getUserName();

        System.out.println(name);*/

        // 使用反射實例化對象 無參數構造函數

        Object newInstance = forName.newInstance();

        // 獲取當前類的 userId字段

        Field declaredField = forName.getDeclaredField("userName");

        // 容許操做私有成員

        declaredField.setAccessible(true);

        // 設置值

        declaredField.set(newInstance, "123");

        User user = (User) newInstance;

        System.out.println(user.getUserName());

 

 

    }

}

 

 

package com.jlong.entity;

 

public class User {

    private String userName;

    private String userId;

    public User(){

 

    }

    public User(String userName){

        this.userName=userName;

    }

 

    public String getUserName() {

        return userName;

    }

 

    public void setUserName(String userName) {

        this.userName = userName;

    }

 

    public String getUserId() {

        return userId;

    }

 

    public void setUserId(String userId) {

        this.userId = userId;

    }

}