elipse的问题

Question

Multiple markers at this line
    - The type java.lang.Object cannot be resolved. It is indirectly referenced from
     required .class files

Answer 1

: 找不到或无法加载主类 tryit.HelloWorld。。。。这是运行后的提示

Answer 2

这是怎么回事？用得好好的，就成这样了