Develop Reference

Java classpath issue '.' vs. './*'

I am trying to compile and run from the command line a simple java hello world program.
It compiles and runs successfully when I do:
> javac HelloWorld.java
> java HelloWorld
However, when I place a jar-dependency in this hello world program and the corresponding jar in the same directory, I run into a classpath issue.
I can compile with:
> javac -cp ./* HelloWorld.java
But I when I attempt to run while specifying the classpath to the jar, my HelloWorld class is not found.
> java -cp ./* HelloWorld
Error: Could not find or load main class HelloWorld
When classpath is ./*, the jar is found but not the class, and when classpath is ., the class is found but not the jar.
I also tried specifying both, but the main class is not found whenever I use a : in the classpath.
> java -cp "./*:." HelloWorld
Error: Could not find or load main class HelloWorld
How can I specify classpath for java to find both the jar and my class?

In powershell, one solution is to use ; instead of :.
I.e. this works in powershell:
> java -cp "./*;." HelloWorld
hello, world
The idea to try that came from an answer to this question:

How to include an external JAR in a directory within the Java classpath and run the Java class?

I have a Java file that contains an external JAR and I want to run it. It is a simple project: https://github.com/eveningstar33/external-jar and I tested it with Java 8 and also with Java 11. The command to create the class file is javac -cp ./lib/* HelloWorld.java and it's working, but if I try to run the class using this command: java -cp ./lib/*:./ HelloWorld it doesn't work and I get this error message:
Error: Could not find or load main class HelloWorld
Caused by: java.lang.ClassNotFoundException: HelloWorld
What should I do to run it? Thank you!

Use java -cp ./lib/* HelloWorld to run the class.
Update:
If the one given above doesn't work, please try with a "" i.e. use java -cp "./lib/*" HelloWorld to run the class.
Another update (tested):
Sorry for posting earlier solutions without testing them myself. Now, I have tested the following to be working:
java -cp .:lib/* HelloWorld

not able to add jar in linux server while executing java class

I am executing 2 java classes which have StringUtils function. For this I have common-lang3.jar so I am giving command
`javac -cp common-lang3.jar *.java`
this time no error but after that
java -cp common-lang3.jar abc.class its giving
Could not find or load main class For linux server where I have to place jar files so that i can just give command javac *.java ? If in classpath java -classpath is not allowing me to edit. pls help

Change
java -cp common-lang3.jar abc.class
to (assuming abc has your main method)
java -cp common-lang3.jar:. abc

Run java program sing Cmd

I'm trying to run Java program using cmd.
When I compile that file using
javac helloworld.java
It works perfectly but when I try to run that file using
java helloworld
I get an error:
couldn't find or load main class.
even though my I put my javac path in class path in system variables and javac working correctly.
After searching on how I can fix it I found that I can use
java -cp . helloworld
because it let you to find .class file.
and it works but I know that I can run java program without this -cp so what this for and how I can run my program without it?

-cp specifies the Java classpath for the JRE you are attempting to start. Look for an environment variable CLASSPATH and add '.'.

-cp is used to set the classpath for the jar file, this flag is same as importing a jar file to eclipse and then use it.
If you want to run without this flag, use should set the classpath first beforing running.
export CLASSPATH=path/to/your/jarfile.jar
If you already have some classpath set
export CLASSPATH=$CLASSPATH:path/to/your/jarfile.jar
If you want to include current directory
export CLASSPATH=$CLASSPATH:path/to/your/jarfile.jar:.

As other have mentioned, you can set the CLASSPATH. However, a much better approach is to bundle the .class files in a JAR ans user java -jar nameofthejar.jar.

Add jar files to classpath at launch time

I want to add some jar files to my binary at runtime, but I keep getting errors. I'm running this on a Windows machine. My code is in a directory called SeleniumTest.
Here is the command I used to compile:
javac SeleniumTest\src\com\src\test\First.java -d SeleniumTest\bin -cp SeleniumTest\lib\junit-4.10.jar;SeleniumTest\lib\selenium-java-2.39.0.jar;SeleniumTest\lib\selenium-server-standalone-2.39.0.jar
This worked successfully. However when I try to run this command:
java -cp SeleniumTest\lib\junit-4.10.jar;SeleniumTest\lib\selenium-java-2.39.0.jar;SeleniumTest\lib\selenium-server-standalone-2.39.0.jar SeleniumTest\bin com.src.test.First
I get a message:
Error: Could not find or load main class SeleniumTest\bin
My code, First.java exists in
SeleniumTest\bin\com\src\test
What am I doing wrong?

try this
java -cp "SeleniumTest\lib\junit-4.10.jar;SeleniumTest\lib\selenium-java-2.39.0.jar;SeleniumTest\lib\selenium-server-standalone-2.39.0.jar;SeleniumTest\bin" com.src.test.First

try following
java -cp SeleniumTest\lib\junit-4.10.jar;SeleniumTest\lib\selenium-java-2.39.0.jar;SeleniumTest\lib\selenium-server-standalone-2.39.0.jar SeleniumTest\bin SeleniumTest\src\com\src\test\First