This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
this is used to indicate the instance variable which is a good coding style.
Your sample code has different variable names. But consider if you have something AB(int pi) Inside the constructor if you say pi, it will indicate the constructor argument, whereas this.pi indicates the instance variable