OOP

Coupling

Types of Modular Coupling

In order of desirability

Data Coupling (weakest most desirable)

Control Coupling

Global Data Coupling

Internal Data Coupling (strongest least desirable)

Content Coupling (Unrated)

Data Coupling

Output from one module is the input to another

Using parameter lists to pass items between routines

Object A passes object X to object B

Object X and B are coupled

A change to X's interface may require a change to B

class Receiver {

public void message( MyType X ) {

// code goes here

X.doSomethingForMe( Object data );

// more code

}

Control Coupling

Passing control flags between modules so that one module controls the sequencing of the processing steps in another module

A sends a message to B

B uses a parameter of the message to decide what to do

class Lamp {

public static final ON = 0;

       public void setLamp( int setting ) {
             if ( setting == ON ) //turn light on
            else if ( setting == 1 ) // turn light off
            else if ( setting == 2 ) // blink }
}

Lamp reading = new Lamp();

reading.setLamp( Lamp.ON );

reading.setLamp( 2 );

Problem: A needs to know the messages it can pass to B.

A Solution:

Decompose the operation into multiple primitive operations

class Lamp {
       public void on() {//turn light on }
       public void off() {//turn light off }
       public void blink() {//blink }

}

Lamp reading = new Lamp();

reading.on();

reading.blink();

Global Data Coupling

Two or more modules share the same global data structures

Example

A method in one object makes a specific reference to a specific external object

Internal Data Coupling

One module directly modifies local data of another module

Example: C++ Friends

Lexical Content Coupling

Some or all of the contents of one module are included in the contents of another

Example: C/C++ header files

Solution: Restrict what goes in header file