Why order in java buildpath is matter?

Question

In Eclipse (Project > Properties > Java Build Path) we have 2 tabs: for adding some libraries into buildpath, and for organizing their order. So, the question is why order in java buildpath is matter?

Answer 1

Because e.g. if you have A.class in two JARs then A.class may be different in these
two JARs. The A.class from the JAR which is first on the path will be the one used.

Suppose you build a library mylib, and you have two versions of it: mylib-1.0.jar
and mylib-1.1.jar. Suppose somebody else uses your library and puts in his Eclipse build
path both JARs. Now, suppose you have a class in both versions of this library/JAR called
com.mycompany.mylib.DatabaseManager. There may be differences between
DatabaseManager from 1.0 and the one from 1.1. So which one of the two
DatabaseManager classes should Eclipse pick up in this case? Answer:
the one from the jar which stands first on your build path.

Answer 2

The first match of the class will be used by JVM.