Question

Consider a scenario that a java program imports the classes from jar files. If the same class resides in two or more jar files there could be a problem.

1. In such scenarios what is the class that imported by the program? Is it the class
   with the older timestamp??

2. What are the practices we can follow to avoid such complications.

Edit : This is an example. I have 2 jar files my1.jar and my2.jar. Both the files contain com.mycompany.CrazyWriter

Answer 1

First, I assume that you mean that the same class resides in two more jar files…

Now, answering your questions:

1. Which class is imported is dependent on your classloader and JVM. You cannot guarantee which class it will be, but in the normal classloader it will be the class from the first jar file on your classpath.
2. Don’t put the same class into multiple jar files, or if you are trying to override system classes, use -bootclasspath.

Edit: To address one of the comments on this answer. I originally thought that sealing the jar would make a difference, since in theory it should not load two classes from the same package from different jar files. However, after some experimentation, I see that this assumption does not hold true, at least with the default security provider.