What is the significance of the reverse domain name for java package structure

java, package

Solution

Globally unique package names avoid naming collisions between libraries from different sources. Rather than creating a new central database of global names, the domain name registry is used. From the JLS:

The suggested convention for generating unique package names is merely a way to piggyback a package naming convention on top of an existing, widely known unique name registry instead of having to create a separate registry for package names.

Problem

Why do we use reverse domain name like com.something. or org.something. structure for java packages? I understand this brings in some sort of uniqueness, but why do we need this uniqueness?

Original source