类加载- JAVA动态性

类加载--- JAVA动态性
类加载学习
隐式动态性
也就是说当自己的程序用到NEW关键字时,就会载入需要载入的类....

  显示的动态性
1. 一个是由java.lang.Class 的forName()方法
2.是由java.lang.ClassLoader 的loadClass()方法


写例子让自己理解下;

interface Assembly{    public void start();}public class Main{    public static void main (String[] args) throws Exception{        Class c=Class.forName(args[0]);        Object o=c.newInstance();        Assembly a=(Assembly) o;        a.start();    }}class A implements Assembly{     public void start(){         System.out.println("class a 使用");     }}class B implements Assembly{    public void start(){        System.out.println("class b 使用");    }}class C implements Assembly{    public void start(){        System.out.println("class c 使用");    }}

动态载入,用到哪个类的时候就载入哪个类.

执行 java -verbose:class Main

[Loaded Main from file:/C:/wang/][Loaded java.lang.IndexOutOfBoundsException from shared objects file][Loaded java.lang.ArrayIndexOutOfBoundsException from shared objects file]Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0        at Main.main(Main.java:6)[Loaded java.lang.Shutdown from shared objects file][Loaded java.lang.Shutdown$Lock from shared objects file]

抛出异常了,界限异常..  没有输入命令行参数......

接着 java -verbose:class Main A

[Loaded java.security.cert.Certificate from shared objects file][Loaded Main from file:/C:/wang/][Loaded Assembly from file:/C:/wang/][Loaded A from file:/C:/wang/]class a 使用[Loaded java.lang.Shutdown from shared objects file][Loaded java.lang.Shutdown$Lock from shared objects file]

先载入主类.. 接口...
载入A类,即可以在不修改主类的情况下增加新的功能..(我没把类分开写.....)

如果写个类D继承了类A ...  会如何..

class D extends A implements Assembly{    public void start(){        System.out.println("class d extends a implements assembly 使用して");    }}

接着: java -verbose:class Main D

[Loaded Main from file:/C:/wang/][Loaded Assembly from file:/C:/wang/][Loaded A from file:/C:/wang/][Loaded D from file:/C:/wang/]class d extends a implements assembly 使用して[Loaded java.lang.Shutdown from shared objects file][Loaded java.lang.Shutdown$Lock from shared objects file]

哦. 是先载入了父类的文件,再载入了子类.....

如果D->C->B->A 依此继承....

[Loaded Main from file:/C:/wang/][Loaded Assembly from file:/C:/wang/][Loaded A from file:/C:/wang/][Loaded B from file:/C:/wang/][Loaded C from file:/C:/wang/][Loaded D from file:/C:/wang/]class d extends a implements assembly 使用して[Loaded java.lang.Shutdown from shared objects file][Loaded java.lang.Shutdown$Lock from shared objects file]

就按循序载入....

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