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In object-oriented programming, encapsulation packages an object's state with the operations that act on it and can restrict direct access to its implementation. It is the object-oriented use of encapsulation.

Information hiding makes an implementation decision the responsibility of one software module, whose API lets other code work without knowing that decision. For a FIFO queue, clients need the removal order and failure behavior; they need not know the current front index in an array. This explains why encapsulation is useful beyond object-oriented programming: procedures with hidden storage can provide the same boundary.^[ref]

In On the Criteria To Be Used in Decomposing Systems into Modules by D. L. Parnas (December 1972, pp. 1054–1056), the example applies a sorting algorithm to word rotations of input lines. One decomposition shares storage layouts among processing stages. The alternative exposes line-storage operations such as CHAR and SETCHAR, hiding whether characters are packed four to a machine word. Changing that packing then belongs to line storage rather than every client. The paper presents a design argument using a deliberately small example, not a universal measured speedup or a claim that classes are required. It also notes that an unnecessarily specified rotation order restricts future implementations (p. 1056, Improvement in Circular Shift Module).