procedures and triggers recompiled automatically?

This is a beginner's question:

If after import I've found some triggers and procedures have INVALID status when querying user_objects, should I worry about it? I thought they will automatically get recompiled when being called.

Please clarify.
Thanks,

For the most part, provided they are actually valid, the objects will be compiled on request. Even so you should consider manually compiling them yourself. I've seen systems with lots of code dependencies grind to a halt due to a cascade effect of compilations.

An easy way to do this is to use either:

$ORACLE_HOME/rdbms/admin/ultrp.sql

or

DBMS_UTILITY.COMPILE_SCHEMA

Cheers