What is the irony in "Hamlet" in Acts 4 or 5???either dramatic, verbal or situational... i need it for applying irony to hamlet..

The first scene of Act 5 takes place in the graveyard and
while the beginning of the scene has some comic relief in the converstations between the
two gravediggers and then the 1st Gravedigger and Hamlet, the end of the scene is very
dramatic.  Laertes first leaps into Ophelia's open grave and proclaims his love for his
sister, then Hamlet rushes into the scene and proclaims his love to be greater than
40,000 brothers' love.  The irony here is that in Act 3, sc. 1, after the "To be, or not
to be..." speech, Hamlet told Ophelia, in line 120, "I loved you not."  The second scene
of Act 5 has several examples of irony as well.  The poisoned tipped sword that was
meant for Hamlet killed Laertes, too.  Hamlet also uses that sword, as well as the
poisoned wine, to kill the one who designed all that means of death for Hamlet -
Claudius.  Finally, Fortinbras, who used great subterfuge throughout the play to get 
his army into Denmark to fight to regain the lands his father lost, becomes king of
Denmark without the need to lift a blade because Hamlet and the rest of the royal family
are all dead.

Act 4 has a great deal of irony in it, too. 
There is much conversational irony in the exchange of words between Hamlet and his two
old friends, Rosencrantz and Guildenstern.  There is situational irony between the acts
of Fortinbras and Hamlet's own inactivity.