Words are slippery. Like Humpty Dumpty proclaimed in Lewis Carroll’s Through the Looking Glass, “When I use a word, it means just what I choose it to mean — neither more nor less.” Certainly the common usage of the words encapsulation and information hiding seems to follow that logic. Authors rarely distinguish between the two and often directly claim they are the same.
Does that make it so? Not for me. Were it simply a matter of words, I wouldn’t write another word on the matter. But there are two distinct concepts behind these terms, concepts engendered separately and best understood separately.
Encapsulation refers to the bundling of data with the methods that operate on that data. Often that definition is misconstrued to mean that the data is somehow hidden. In Java, you can have encapsulated data that is not hidden at all.
However, hiding data is not the full extent of information hiding. David Parnas first introduced the concept of information hiding around 1972. He argued that the primary criteria for system modularization should concern the hiding of critical design decisions. He stressed hiding “difficult design decisions or design decisions which are likely to change.” Hiding information in that manner isolates clients from requiring intimate knowledge of the design to use a module, and from the effects of changing those decisions.