自建 java Lang String 类

package java.lang;

public class String {
     public  String a="aaaaa";
}

public class Test {

    public static void main(String[] args) {
            String a=new String();
            System.out.println(a.a);
    }
}

输出

Exception in thread "main" java.lang.NoSuchFieldError: a
    at chaogemianshi.src.main.Test.main(Test.java:12)

双亲委派机制
http://blog.youkuaiyun.com/u011080472/article/details/51332866