What Is Classpath And How To Set That In Java

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In java, the source file is written in normal text and saved with .java  extension.
The compiler upon invoked by the command javac creates a .class file for the corresponding .java file.
The JVM during run time reads the .class file ,performs certain checks and execute the same.
if the .class file is placed under …../java/bin/ folder . It is not required to mention classpath. But when our project becomes larger, it is required to create some folder structure and place all the necessary .class file at one place,it is extremely required for JVM to know where the .class files resides.

This post will talk about the different settings how to set classpath in different way.

 

Classpath settings

How to set classpath for java…

  • In my previous post here, I have shown how to set classpath permanently from environment variable
  • Temporary for a command session
    set classpath=%classpath%;E:myPrograms
    //%classpath% is to keep what ever is already present in the classpath;Now provide the required classpath followed by a semi colon(;)
    

    This command is valid for the command prompt it has been set. If you open another command prompt the java command will not work.

  • One more option is also available for setting classpath, valid for a single command.
    java -cp <<full classpath>> <<name of the class>>
    like-java -cp E:myProgram Test123

The scope of the process:

  • Set globally–across the command prompts
  • Set classpath at command prompt–only for that command prompt session
  • Set classpath on command level-only for that command

While going for the 3rd option there are things to remember:

  • -cp will not consider present working directory by default. We need to include dot(.) to get present working directory into classpath
  • Always use full path while working with -cp
  • if the same class file available in different directories then JVM will read from left to write for the -cp command and whenever the first occurrence of the class is available JVM will pick that and execute. But the next sequence will not be picked again.


so in drive C,D,E three test class is available.
Now if we provide

java -cp C:;D:;E: test 

only C: drives test will be executed,D and E will be ignored.
similarly if we provide

java -cp D:;C:;E: test

only D: drives test will be executed,C and E will be ignored.

what are the differences Between Path And Classpath In Java?

Let us understand what is path in java..
In java path is the variable which holds the specific location of the binary executable files of java like- java/javac etc

How to set path–
Well there are two ways by which we can set path

  • Permanently set path via environment variable-(click here for more)
  • Temporary for a session.

we will check out how to set path temporarily ..

Temporary settings:
1. Go to start–>run –>type cmd

2. click on ok. It will open command prompt for windows

3. Now navigate to the path where you have installed your java(JDK installation folder)
it might be C:Program Filesjavajdk<<version>>

4. Copy the path and come back to command prompt.
5. Type the below written command:

set path=C:Program FilesJavajdk1.7.0_21bin

 

 

you are done!! Now you can write any java program and compile the same.

Classpath:

Classpath is the variable which is used to tell JVM from where all my classes are residing. and from which location it has to pick the required .class files.

How to Recognize The Java Classpath?

This posting is about a tiny uncomplicated assortment of batch files which can be utilised to check the habits of the javac compiler and java course launcher for different classpath scenarios. The process is called ClasspathTester . Down load recommendations are integrated at the conclude of this write-up.

When you are in the middle of striving to debug a java build it is a terrible time to check out to boil every thing down to a very simple take a look at case, so basically the intent of my examination selection is to do this for you forward of time. If you can not locate the specific take a look at you want, it is uncomplicated to modify the existing assessments or make a new check to fit your desires.

How ClasspathTester Works?

As formerly mentioned, I did almost everything with batch files, because I needed the assessments to be as uncomplicated, portable (within the Home windows atmosphere), and easy as feasible. There are a couple of helper batch documents to do things like generate formatted output and establish a listing composition, but or else approximately all of the get the job done is performed in the RunAllTests.bat file.

What RunAllTests.bat consist of is checks and sub-assessments. If you have not downloaded it however, I propose you download it and take a look. Just about every take a look at consist of some type of a set up. Setup generally entails the next:

1. Examination setting is cleaned up of previous directories, files, and classpath.

2. New listing construction is designed, new data files are created and put in proper directories, and the classpath is set if important.

Following setup, the checks are run. This is made up of functioning both the javac.exe compiler, the java.exe launcher, or each. That’ all there is to it.

A Uncomplicated Case in point

To understand what ClasspathTester , does, open the RunAllTests.bat file in your text editor and appear at Exam1 . Just about every take a look at is a collection of sub-checks which are loosely grouped all around some kind of a central tests theme, and Examination1 is 1 of the simplest.

So what comes about in Take a look at1 ? Very first it phone calls banner.bat to insert a header to the benefits file. Then it creates the Howdy.java and MyLibClass.java documents, by copying them from their corresponding avaj files (the explanation for employing avaj information is talked about later on in this short article). Now anything is established up to run some subtests.

Examination1A is extremely simple. According to its description, “The Good day.java file is positioned in the recent listing, and the Hello.class file will be penned to the recent directory and run from the recent directory”. As you can envision, Examination1A operates flawlessly.

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