CSC/ECE 517 Fall 2009/wiki3 20 i7: Difference between revisions
Jump to navigation
Jump to search
No edit summary |
|||
| Line 1: | Line 1: | ||
= Liskov substitution principle = | = Liskov substitution principle = | ||
The Liskov substitution principle was introduced by Barbara Liskov in 1987 and is concerned with subtype contractual correctness. Based on a paper from 1994 the principle states, "Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T.". This means that for every parent type T, subtype S should be able to be substituted in for it and the behavior of the program should remain exactly the same. | The Liskov substitution principle was introduced by Barbara Liskov in 1987 and is concerned with subtype contractual correctness. Based on a paper from 1994 the principle states, "Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T.". This means that for every parent type T, subtype S should be able to be substituted in for it and the behavior of the program should remain exactly the same. The following example in Java illustrates the the principle. | ||
==Preconditions== | ==Preconditions== | ||
Revision as of 08:56, 18 November 2009
Liskov substitution principle
The Liskov substitution principle was introduced by Barbara Liskov in 1987 and is concerned with subtype contractual correctness. Based on a paper from 1994 the principle states, "Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T.". This means that for every parent type T, subtype S should be able to be substituted in for it and the behavior of the program should remain exactly the same. The following example in Java illustrates the the principle.
Preconditions
Preconditions cannot be strengthened. <Explain in english> <Example>
Postconditions
Postconditions cannot be weakened. <Explain in english>
Invariants
Invariants must be preserved. <Explain in english>