how to a class if dont have its .java file.

In eclipse

.java files reside in "src" folder and .class file reside in "bin" folder.

i have a class name "a.class" in bin folder, of which i dont have source file or .java file.. now i want to use this a.class in another java program.
is it necessary to have source file also . coz whenever i use this a.class file in other program i get error.. how to use it without its .java file

You will need to add the class to your classpath.
Best is to package the class into a jar file and add that jar file to your project's build path.

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You will need to add the class to your classpath.
Best is to package the class into a jar file and add that jar file to your project's build path.

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can you please explore in steps , how to do this .

Google "how to create a jar file" and read the first link that comes up.

i made jar ... added external jar to build path.. and now the erroe is

Code:

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Exception in thread "main" java.lang.NoClassDefFoundError: com/asprise/util/ocr/OCR
        at Hi.main(Hi.java:21)
Caused by: java.lang.ClassNotFoundException: com.asprise.util.ocr.OCR
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
        ... 1 more

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You need the asprise.jar file to be on your classpath when running the application.

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You need the asprise.jar file to be on your classpath when running the application.

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And how can we do this ?

The same way you added the external jar to the build path.

The same way you added the external jar to the build path.

asprise.jar ?

the jar i made is OCR.jar. i dont have any jar called asprise.jar

You are attempting to use com/asprise/util/ocr/OCR which is in asprise.jar. So get the asprise.jar rather than incorrectly trying to make your own.