How can an object be unreferenced?

There are many ways:

By nulling the reference
By assigning a reference to another
By anonymous object etc.

By nulling a reference:

$\begin{lstlisting} Employee e=new Employee(); e=null; \end{lstlisting}$

By assigning a reference to another:

$\begin{lstlisting} Employee e1=new Employee(); Employee e2=new Employee(); e1=... ...irst object referred by e1 is available for garbage collection \end{lstlisting}$

By anonymous object:

$\begin{lstlisting} new Employee(); \end{lstlisting}$