How To Set Java Classpath In Linux Command Line

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How to Gear up CLASSPATH in Java

CLASSPATH: CLASSPATH is an environment variable which is used by Awarding ClassLoader to locate and load the .grade files. The CLASSPATH defines the path, to find 3rd-political party and user-divers classes that are not extensions or function of Java platform. Include all the directories which contain .class files and JAR files when setting the CLASSPATH.

Yous demand to prepare the CLASSPATH if:

You demand to load a class that is non nowadays in the current directory or whatever sub-directories.
You need to load a class that is non in a location specified by the extensions mechanism.

The CLASSPATH depends on what you are setting the CLASSPATH. The CLASSPATH has a directory name or file name at the end. The post-obit points describe what should be the end of the CLASSPATH.

If a JAR or nil, the file contains class files, the CLASSPATH end with the proper noun of the zip or JAR file.
If grade files placed in an unnamed package, the CLASSPATH ends with the directory that contains the grade files.
If course files placed in a named parcel, the CLASSPATH ends with the directory that contains the root package in the full package proper noun, that is the outset package in the full package proper name.

The default value of CLASSPATH is a dot (.). It means the only electric current directory searched. The default value of CLASSPATH overrides when you set up the CLASSPATH variable or using the -classpath command (for short -cp). Put a dot (.) in the new setting if you desire to include the current directory in the search path.

If CLASSPATH finds a class file which is present in the current directory, and then information technology volition load the grade and use it, irrespective of the same name form presents in another directory which is also included in the CLASSPATH.

If you want to gear up multiple classpaths, then you need to separate each CLASSPATH by a semicolon (;).

The third-party applications (MySQL and Oracle) that use the JVM can modify the CLASSPATH environment variable to include the libraries they apply. The classes tin be stored in directories or archives files. The classes of the Java platform are stored in rt.jar.

There are two ways to ways to prepare CLASSPATH: through Command Prompt or past setting Environs Variable.

Allow's see how to set CLASSPATH of MySQL database:

Step 1: Click on the Windows button and choose Command Panel. Select Organization.

Step 2: Click on Advanced System Settings.

Footstep 3: A dialog box will open. Click on Environs Variables.

Stride four: If the CLASSPATH already exists in System Variables, click on the Edit button then put a semicolon (;) at the terminate. Paste the Path of MySQL-Connector Java.jar file.

If the CLASSPATH doesn't exist in System Variables, then click on the New push button and type Variable name every bit CLASSPATH and Variable value equally C:\Program Files\Java\jre1.8\MySQL-Connector Java.jar;.;

Remember: Put ;.; at the end of the CLASSPATH.

Departure between PATH and CLASSPATH

PATH	CLASSPATH
PATH is an environment variable.	CLASSPATH is also an environment variable.
It is used by the operating system to discover the executable files (.exe).	It is used past Awarding ClassLoader to locate the .course file.
Y'all are required to include the directory which contains .exe files.	Yous are required to include all the directories which comprise .class and JAR files.
PATH environment variable once set, cannot be overridden.	The CLASSPATH environment variable can be overridden by using the command line selection -cp or -CLASSPATH to both javac and java control.

How to Set CLASSPATH in Windows Using Command Prompt

Type the following command in your Control Prompt and press enter.

In the above command, The set is an internal DOS control that allows the user to change the variable value. CLASSPATH is a variable proper noun. The variable enclosed in percentage sign (%) is an existing surroundings variable. The semicolon is a separator, and after the (;) there is the PATH of rt.jar file.

How ext folder works in Coffee

The ext directory works a bit like the CLASSPATH. ext directory is the part of the class loading mechanism. The classes which are available within JARs in the ext directory are available to Coffee applications.

The following table demonstrates the key deviation between the CLASSPATH and Extension Mechanism:

Characteristics	CLASSPATH	Extension Mechanism
Grade loading club	CLASSPATH loads after bootstrap and extension loading.	ext loads subsequently bootstrap loading but before CLASSPATH loading.
Scope	It is an application specific. All JREs on the host is the CLASSPATH environs variable.	All JVMs are running in specific JRE coffee.ext.dirs.
Package name	coffee.class.path is used to find the directories and JAR archives containing grade files.	coffee.ext.dirs is used to specify where the extension machinery loads classes.
Specification	It is specified by name including the extension.jar and directory containing .grade files.	All JAR files in specified directories are loaded.

The mechanism will pick up all .jar files from the extension directory even if the file does non accept the .jar extension. The implementation of this is that if one tin can change the name of a jar placed in a classpath directory to take an extension other than .jar. The wildcard (*) does not pick it up. This technique will not work with the extension directory.

Permit'due south understand the execution process through an instance.

A.java

B.coffee

Compile the A.java file. we will archive the compiled A.class file into A.jar. Place this JAR file into some other directory than the compiled B.grade file.

To demonstrate the use of the classpath, we place the A.jar file in a directory C:\JavaPrograms and volition access that JAR through wildcard (*) for B to use.

We plant that B tin still load the A.class while we had deleted it from the current directory. The Java launcher was explicitly looked for C:\JavaProgram. Information technology is as well possible to take the grade loaded without its presence in the same directory and explicit classpath specification.

Information technology is often referred to as a do good of Using the extension machinery because all applications which are using that JRE can see the same classes without the need to specify them on the classpath explicitly.

What happens if we change the name of A.jar into A.backup in the aforementioned CLASSPATH-referenced directory. NoClassDefFoundError is encountered when nosotros do the same because the CLASSPATH-reference does not accept the .jar extension.

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