Why do we need Maven or Ant, if we already have Eclipse?

Question

I think this question is an extension of Compare to the IDE for Java,do we still need Ant?

There are answers for the question above, but I wish to know a concrete ex

Answer 1

Maven and Ant are used to script builds so that they may be executed in batch jobs like with Jenkins or on the command line.

In fact Eclipse itself uses Ant extensively to build plugins.

If you were to learn one of the two, learn Maven, it's the one pretty much everyone uses these days (replacing Ant).