The Book of Ruby

The One-Way-In, One-Way-Out Principle

In most modern object-oriented languages such as Java and C#, encapsulation and information hiding are not rigorously enforced. In Smalltalk, on the other hand—the most famous and influential object-oriented language—encapsulation and information hiding are fundamental principles: If you send a variable x to a method y and the value of x is changed inside y, you cannot obtain the changed value of x from outside the method—unless the method explicitly returns that value.

Encapsulation or Information Hiding?

Often these two terms are used interchangeably. To be nitpicky, however, there is a difference. Encapsulation refers to the grouping together of an object’s “state” (its data) and the operations that may alter ...