Encapsulation is the process of information hiding and encapsulation in OOP is due to interaction of user(... another object). There is only way to get method (operation to be performed on object) execute is the messaging. user doesn't know about internal myths of object (or blueprint : Class). this property makes encapsulation possible.

Several authors and OO guru also argue about attributes encapsulation. because in functional programming languages you need to manage data separately in the form of variables (includes local and global) but in OOP each contains its associated data and operations in itself(in the form of attributes and methods generally speaking class members).