Coupling Not what first comes to mind Copyright

Coupling • Coupling, in Computer Science and Software Engineering, describes the dependency of one

Terminology • Low coupling is sometimes referred to as weak or loose – Generally

Informal Example • The coupling of a customer and clerk in a store is

Types of Coupling 1 • Content (high) – A module relies on the internal

Types of Coupling 2 • Control (medium) – One module controls the execution of

Types of Coupling 3 • Data (low) – Data is shared, but the data

Coupling Issues • Highly coupled systems become harder to maintain • A change in

Some Examples • GUI programs are typically Common coupled – Event handlers rely on

The Date class example • The methods are stamp or common coupled with one

Date again • Suppose that the correct function were missing and not called •

High Coupling is Not Evil • Very often we have a program that has

The Other Coupling • Multiple CPU systems also use this term • Two CPUs

Conclusion • When designing classes we generally want the lowest possible coupling – This

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Coupling • Coupling, in Computer Science and Software Engineering, describes the dependency of one thing upon another – The things in question are usually functions and objects – May also refer to interdependency • Low coupling means an item is not very dependent on another • High coupling means that we cannot use the one without the other Copyright © 2014 by Curt Hill

Terminology • Low coupling is sometimes referred to as weak or loose – Generally desirable for functions and objects – Indicates well designed modules • High coupling – AKA tight or strong – Inhibits reuse in other programs Copyright © 2014 by Curt Hill

Informal Example • The coupling of a customer and clerk in a store is low – Communicate through common language – Either person is interchangeable with another • Family relationships are usually high – Parents/siblings/spouse are tightly coupled – No interchangeability Copyright © 2014 by Curt Hill

Types of Coupling 1 • Content (high) – A module relies on the internal workings of another • Common (high to medium high) – Two modules use common global variables – Changing the globals requires a change in the modules • External (medium) – Two modules share a common data format or protocol Copyright © 2014 by Curt Hill

Types of Coupling 2 • Control (medium) – One module controls the execution of another – Often a parameter that alters the type of processing • Stamp or data structure – Two modules use a common data structure, but not the same portions of it – Changing the data structure may mandate changes in one without the other Copyright © 2014 by Curt Hill

Types of Coupling 3 • Data (low) – Data is shared, but the data is simple, such as in parameters – Often a parameter that alters the type of processing • None – Two modules share nothing Copyright © 2014 by Curt Hill

Coupling Issues • Highly coupled systems become harder to maintain • A change in one module forces changes in others • A ripple effect occurs as change ripples through the system Copyright © 2014 by Curt Hill

Some Examples • GUI programs are typically Common coupled – Event handlers rely on the fact that certain edit boxes or labels are available – Cutting the event handler out of one program and putting it into another is never done • Math library functions – Those programs that use them are Data coupled to them – They are not coupled to each other Copyright © 2014 by Curt Hill

The Date class example • The methods are stamp or common coupled with one another – get. Day is stamp coupled with get. Month – To. String is common coupled with get. Day – Changing the form of the month, day and year mandates changes in every method • Since the class is a unit this is not a problem Copyright © 2014 by Curt Hill

Date again • Suppose that the correct function were missing and not called • Then the date class would be dependent on its client to supply good data • This would shift the checking to the client • This would increase the coupling between the client and the class Copyright © 2014 by Curt Hill

High Coupling is Not Evil • Very often we have a program that has a central data structure or many data structures • Nearly every method/function uses one or more of these • We do not need to pass every data structure to every function – Just use it as global data – This is not bad but it prevents reuse of the function Copyright © 2014 by Curt Hill

The Other Coupling • Multiple CPU systems also use this term • Two CPUs that have a common memory is termed tightly coupled • Two CPUs that are connected by some other type of high speed communications is loosely coupled • Current multicore CPUs are tightly coupled, while the CPU to GPU coupling is loose Copyright © 2014 by Curt Hill

Conclusion • When designing classes we generally want the lowest possible coupling – This allows us to reuse the class – This allows us to rewrite the class without breaking other things • Many programs have one-shot classes – They are designed for this particular application – Little chance of reusability Copyright © 2014 by Curt Hill