Multi-format calculator - Software Development Case Studies in Java - page 129

Calculator

<< abstract >>
Format

Command FractionalFormat FixedPointFormat FloatingPointFormat

create

Figure 6.4 The classes that handle number format conversions

Sidebar 6.1 Dynamic behaviour

The problem of changing the behaviour of a program (or some of its parts) at run
time is very common.
Let's focus on a simplified version of this problem. We consider a class
( Changing ) that has an entry method ( public void perform() ) whose behaviour can
vary during the execution of the program, and method public void setBehavior()
used to switch from one behaviour to the other. There are two possible solutions:

to implement all the possible behaviours inside method perform() using a big
switch construct that selects the code to be executed;

■

to encapsulate every specific behaviour in a different object to be passed to
class Changing .

■

The first solution requires a status attribute that keeps track of the current
behaviour. The entry method contains a switch (or chain of else - if) to select the
appropriate behaviour.
This solution is quite simple: class Changing contains the entry method and the
behaviour selection method.

public class Changing {
int behavior # 0;
public static final int FIRST_BEHAVIOR # 1;
public static final int SECOND_BEHAVIOR # 2;
public void setBehavior( int newBehavior){ behavior # newBehavior; }
public void perform(){
switch (behavior){
case 1: /* B1 */
case 2: /* B2 */
}

}

}

The following code fragment shows the use of this solution:

Changing chObject # new Changing(;
chObject.setBehavior(Changing.FIRST_BEHAVIOR);
chObject.perform();