Question

Investigate and discuss the main principles of Design By Contract and in which programming languages are these supported.

Answer 1

• Design By Contract is one of the approach that is used to design software.
• Design by contract programming, contract programming is the same as Design by Contract.
• This technique is developed by Bertrand Meyer .
• The main idea behind this design is assertion which is a Boolean statement and its value should be always true .
• The value of assertion can be false only when there is bug in the program.
• The assertions are mainly checked during the stage of debugging.
• Mainly there are three kinds of assertions.
• They are post-conditions, pre-conditions, and invariant.
• Post-condition is a statement that says that what it should be after an operation.
• An example of post-condition is sum = object_1 + object_2 .
• Pre-condition is a statement that contains some conditions. This statements gives some condition that are to be checked before executing an operation.
• An example of Pre-condition is, something should be greater than or equal to zero. It decide which data is meaningful.
• Invariant is based on the instances of class. It should be always true for the the instances of a class.
• Programming languages that support Design By Contract : Java, C#, Ruby, Python, JavaScript etc...