| Objects communicate with one another by sending or receiving information to or from each other. A message for an object is a request for execution of a procedure and therefore will invoke a function in the receiving object that generates the desired results. Message passing involves specifying the name of the object, the name of the function and the information to be sent. |
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For example, in the car-dealer case study, the
main method has the following message passing:
public class TestVehicle {
public static void main( String[ ] args ) {
...
Sale veh1 = new Sale( "FG1000", args[0], "B-Class", 100000.00, 25000 );
((Sale) veh1).setDepreciation( 20.0 );
...
}
}
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Cohesion
Cohesion refers to the level of a component which performs a single well-defined task. A single well-defined task is done by a highly cohesive method. The weakly cohesive method will split the task into separate parts. The
java.io package is a highly cohesive package because it has I/O related classes and interfaces.
However, the java.util package is a weakly cohesive package because it has unrelated classes and interfaces.