Why Does \"java Echo \\\"hello\\\"\" Fail and How to Fix It?

Executing a Java .class File from the Command Line

When attempting to run a compiled Java class (Echo.class) from the command line using "java Echo "hello"", the following error may occur: "java.lang.NoClassDefFoundError: Echo". This indicates that the Java Virtual Machine (JVM) cannot find the class definition for "Echo".

To resolve this issue, you need to specify the classpath when running the command. The classpath is an environment variable that defines the path where the JVM should search for .class files. By including the current directory (".") in the classpath, the JVM can locate the Echo.class file.

Therefore, the correct command to execute the Java class from the command line is:

java -cp . Echo "hello"

This command specifies the current directory as part of the classpath (-cp .) and then calls the Echo class (Echo) with the provided argument ("hello").

Alternatively, you can set the CLASSPATH environment variable to include the current directory and then run the command without specifying the classpath. For instance:

SET CLASSPATH=%CLASSPATH;.
java Echo "hello"

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