i have tried compiling java programs on the command line ( terminal ) , but it has failed , the gcj shows an error something lik '/usr/lib/gcc4./../../../ , bad reference to main ' , i do not understand this ,.... i use FC 6 , and i have Eclipse IDE on it , i do not know how to use it , and when i open it , the whole system gets slow , nothing else works , everything hangs up , ... even gcc with '-x java' option shows error ,...please help me !

Why don't you install sun jdk? As for Eclipse being slow, that may be related to the amount of RAM that is available to you. Eclipse is quite demanding in resources (if I remember correctly, the windows version required 1GB of RAM to run fluently - I don't think the Linux version can't be far off). And there is excellent documentation on Eclipse.org if you need to get familiar with it; it's well worth the trouble reading it if you want to develop java applications of a certain complexity. Netbeans IDE can be an alternative but if you don't understand Eclipse, I doubt whether you'll find Netbeans any easier to use.