Java反射中Class.forName和classloader的区别

Java中Class.forName和classloader都可以用来对类进行加载。

Class.forName除了将类的.class文件加载到jvm中之外，还会对类进行解释，执行类中的static块。

而classloader只干一件事情，就是将.class文件加载到jvm中，不会执行static中的内容，只有在newInstance才会去执行static块。

Class.forName(name,initialize,loader)带参数也可控制是否加载static块。并且只有调用了newInstance()方法采用调用构造函数，创建类的对象。

代码如下：

 package com.mangosoft.java.reflect;

 /**
  * Created by zhangshengjian on 2017/3/1.
  */
 public class Line {
     static {
         System.out.println("static code executing: loading line...");
     }
 }

 package com.mangosoft.java.reflect;

 /**
  * Created by zhangshengjian on 2017/3/1.
  */
 public class Point {
     static {
         System.out.println("static code executing: loading point...");
     }
 }

 package com.mangosoft.java.reflect;

 /**
  * classloader和Class.forName的区别
  *
  * Created by zhangshengjian on 2017/3/1.
  */
 public class ClassLoaderAndForNameTest {

     public static void main(String[] args) {
         String wholeNameLine = "com.mangosoft.java.reflect.Line";
         String wholeNamePoint = "com.mangosoft.java.reflect.Point";

         System.out.println("classloader testing...");
         testClassLoader(wholeNameLine, wholeNamePoint);
         System.out.println("---------------------------------------");
         System.out.println("Class.forName testing...");
         testForName(wholeNameLine, wholeNamePoint);
     }

     //classloader
     public static void testClassLoader(String wholeNameLine, String wholeNamePoint) {
         ClassLoader loader = ClassLoader.getSystemClassLoader();
         Class<?> line;
         Class<?> point;
         try {
             line = loader.loadClass(wholeNameLine);
             point = loader.loadClass(wholeNamePoint);
             System.out.println("line " + line.getName());
             System.out.println("point " + point.getName());
         } catch (ClassNotFoundException e){
             e.printStackTrace();
         }
     }

     //Class.forName
     public static void testForName(String wholeNameLine, String wholeNamePoint) {
         try {
             Class line = Class.forName(wholeNameLine);
             Class point = Class.forName(wholeNamePoint);
             System.out.println("line " + line.getName());
             System.out.println("point " + point.getName());
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         }
     }
 }

运行结果如下：