java socket异常_Java Socket异常

我试图用Java编写一个简单的客户端服务器程序： - 在同一台机器上运行服务器和客户端代码......但是在运行时遇到错误： -

java.net.ConnectException: Connection refused: connect

at java.net.PlainSocketImpl.socketConnect(Native Method)

at java.net.PlainSocketImpl.doConnect(Unknown Source)

at java.net.PlainSocketImpl.connectToAddress(Unknown Source)

at java.net.PlainSocketImpl.connect(Unknown Source)

at java.net.SocksSocketImpl.connect(Unknown Source)

at java.net.Socket.connect(Unknown Source)

at java.net.Socket.connect(Unknown Source)

at java.net.Socket.(Unknown Source)

at java.net.Socket.(Unknown Source)

at Requester.run(Requester.java:13)

at Requester.main(Requester.java:68)

Exception in thread "main" java.lang.NullPointerException

at Requester.run(Requester.java:45)

at Requester.main(Requester.java:68)

谁能帮忙！