课程源码运行不了

点南放入购物车，出现以下错误：

ype Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception

root cause

java.lang.Error: Unresolved compilation problems:
The type java.util.Map$Entry cannot be resolved. It is indirectly referenced from required .class files
Map.Entry cannot be resolved to a type
The method entrySet() from the type HashMap<Items,Integer> refers to the missing type Map$Entry
Map.Entry cannot be resolved to a type

entity.Cart.<init>(Cart.java:1)
servlet.CartServlet.addToCart(CartServlet.java:110)
servlet.CartServlet.doPost(CartServlet.java:72)
servlet.CartServlet.doGet(CartServlet.java:49)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.2 logs.

Apache Tomcat/7.0.2