eclipse - Java Build Path - Add External JARs' and Add Variable -

what difference between java build path - add external jars button , add variable button functionality, why required. please explain in detail.

both can used achieve same thing: add jar build path.

suppose have project p1 wants use jar installed supplier s1, happens located @ c:\s1\aproject\jars\useful.jar

client add external jars, navigate, select, , we're done.

but, consider these cases.

1). suppose have several projects want use same jar? end repeating projects p1-pn. gets dull. what's worse, suppose install new version of s1's stack, need update project's build paths reference

c:\s1\aproject-**v2**\jars\useful.jar 

and what's worse, if miss 1 running 2 versions of jar may bad!

2). share project colleage happens have s1 product installed in different location. need amend project point to

 e:\myfavouritethings\s1\aproject\jars\useful.jar 

and if using scm may tread on each others toes.

so:

instead add variable allows define workspace variable (ie. specific environment) can used reference jar

 $(s1_jars)\\useful.jar 

now single place update new version of s1, , each developer can set own value s1_jars.

i recommend using variables non-trivial development scenarios.