What is a classpath?

Question

I was just reading this line:

The first thing the format() method does is load a Velocity template from the classpath named output.vm

And I couldn't figure out what was meant by classpath in this context.

Answer 1

classpath and path are the evironment variables . usually , you have to put the jdk/bin to path so that u could use java compiler everywhere , classpath is the path of your .class files . the classpath has a default path a period(.) which means the current directory. but when u used the packages . u would either specify the full path of the .class file or put the .class file path in the classpath which would save a lots of works !

Answer 2

CLASSPATH is an environment variable (i.e., global variables of the operating system available to all the processes) needed for the Java compiler and runtime to locate the Java packages used in a Java program. (Why not call PACKAGEPATH?) This is similar to another environment variable PATH, which is used by the CMD shell to find the executable programs.

CLASSPATH can be set in one of the following ways:

CLASSPATH can be set permanently in the environment: In Windows, choose control panel ⇒ System ⇒ Advanced ⇒ Environment Variables ⇒ choose "System Variables" (for all the users) or "User Variables" (only the currently login user) ⇒ choose "Edit" (if CLASSPATH already exists) or "New" ⇒ Enter "CLASSPATH" as the variable name ⇒ Enter the required directories and JAR files (separated by semicolons) as the value (e.g., ".;c:\javaproject\classes;d:\tomcat\lib\servlet-api.jar"). Take note that you need to include the current working directory (denoted by '.') in the CLASSPATH.

To check the current setting of the CLASSPATH, issue the following command:

> SET CLASSPATH

CLASSPATH can be set temporarily for that particular CMD shell session by issuing the following command:

> SET CLASSPATH=.;c:\javaproject\classes;d:\tomcat\lib\servlet-api.jar

Instead of using the CLASSPATH environment variable, you can also use the command-line option -classpath or -cp of the javac and java commands, for example,

> java –classpath c:\javaproject\classes com.abc.project1.subproject2.MyClass3

Answer 3

Think of it as Java's answer to the PATH environment variable - OSes search for EXEs on the PATH, Java searches for classes and packages on the classpath.

Like the springsteen-esque question, too.

Answer 4

The classpath in this context is exactly what it is in the general context: anywhere the VM knows it can find classes to be loaded, and resources as well (such as output.vm in your case).

I'd understand Velocity expects to find a file named output.vm anywhere in "no package". This can be a JAR, regular folder, ... The root of any of the locations in the application's classpath.

Answer 5

Static member of a class can be called directly without creating object instance. Since the main method is static Java virtual Machine can call it without creating any instance of a class which contains the main method, which is start point of program.

Answer 6

Setting the CLASSPATH System Variable

To display the current CLASSPATH variable, use these commands in Windows and UNIX (Bourne shell): In Windows: C:\> set CLASSPATH In UNIX: % echo $CLASSPATH

To delete the current contents of the CLASSPATH variable, use these commands: In Windows: C:\> set CLASSPATH= In UNIX: % unset CLASSPATH; export CLASSPATH

To set the CLASSPATH variable, use these commands (for example): In Windows: C:\> set CLASSPATH=C:\users\george\java\classes In UNIX: % CLASSPATH=/home/george/java/classes; export CLASSPATH