Running Java Program from Command Line Linux

Question

I am not very experience with java and this is driving me crazy. I wrote a java program FileManagement and I need to run it from the command line.

I can compile it from the command line with javac FileManagement/*.java which will create all the classes in that folder but when I try java FileManagement.Main it says :

Exception in thread "main" java.lang.NoClassDefFoundError: FileManagement/Main

The thing is that I have tried this same procedure in a remote computer and it is working fine. It is not working on mine.

Answer 1

If your Main class is in a package called FileManagement , then try:

java -cp . FileManagement.Main

in the parent folder of the FileManagement folder.

If your Main class is not in a package (the default package) then cd to the FileManagement folder and try:

java -cp . Main

More info about the CLASSPATH and how the JRE find classes:

• How Classes are Found
• Setting the class path (Solaris/Linux)
• http://en.wikipedia.org/wiki/Classpath_(Java)

Answer 2

Guys let's understand the syntax of it.

1. If class file is present in the Current Dir.

   java -cp . fileName

2. If class file is present within the Dir. Go to the Parent Dir and enter below cmd.

   java -cp . dir1.dir2.dir3.fileName

3. If there is a dependency on external jars then,

   java -cp .:./jarName1:./jarName2 fileName

   Hope this helps.

Answer 3

(This is the KISS answer.)

Let's say you have several .java files in the current directory:

$ ls -1 *.java
javaFileName1.java
javaFileName2.java

Let's say each of them have a main() method (so they are programs, not libs), then to compile them do:

javac *.java -d .

This will generate as many subfolders as "packages" the .java files are associated to. In my case all java files where inside under the same package name packageName , so only one folder was generated with that name, so to execute each of them:

java -cp . packageName.javaFileName1
java -cp . packageName.javaFileName2

Answer 4

What is the package name of your class? If there is no package name, then most likely the solution is:

java -cp FileManagement Main