有关这章的问题

按照课程代码敲了遍，运行后结果如下

java.net.BindException: Address already in use: JVM_Bind

at java.net.DualStackPlainSocketImpl.bind0(Native Method)

at java.net.DualStackPlainSocketImpl.socketBind(DualStackPlainSocketImpl.java:106)

at java.net.AbstractPlainSocketImpl.bind(AbstractPlainSocketImpl.java:382)

at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:190)

at java.net.ServerSocket.bind(ServerSocket.java:375)

at java.net.ServerSocket.<init>(ServerSocket.java:237)

at java.net.ServerSocket.<init>(ServerSocket.java:128)

at com.imooc.Server.main(Server.java:21)

请问这个怎么解决？（老师敲得代码下载下来导入运行后也是这个结果）-_-