Figure 10-15 depicts the checking code for the addPlayer() method of Tournament. Write the checking code for the other constraints associated with Tournament depicted in Figure 9-16.

Question

What will be an ideal response?

Answer 1

Figure 10-10 depicts the checking code for Tournament.removePlayer(). The key points are that
• preconditions are checked first,
• some values may have to be saved for checking postconditions before the real work is done,
• postconditions and invariants are checked after the real work is done, and
• the conditions checked (i.e., the conditions under which an exception should be raised) are the opposite of the
conditions stated in the contracts (i.e., the conditions that should always be true).
```
public class Tournament {
//...
private List players;
public void removePlayer(Player p) throws UnknownPlayer, KnownPlayer,
IllegalNumPlayers, IllegalLeague, IllegalName
{
// check precondition isPlayerAccepted(p)
if (!isPlayerAccepted(p)) {
throw new UnknownPlayer(p);
}
// check precondition getNumPlayers() < maxNumPlayers
if (getNumPlayers() == getMaxNumPlayers()) {
throw new TooManyPlayers(getNumPlayers());
}
// save values for postconditions
int pre_getNumPlayers = getNumPlayers();
// accomplish the real work
players.add(p);
p.addTournament(this);
// check post condition !isPlayerAccepted(p)
if (isPlayerAccepted(p)) {
throw new KnownPlayer(p);
}
// check post condition getNumPlayers() = @pre.getNumPlayers() - 1
if (getNumPlayers() != pre_getNumPlayers - 1) {
throw new IllegalNumPlayers(getNumPlayers());
}
// check invariant maxNumPlayers > 0
if (getMaxNumPlayers() <= 0) {
throw new IllegalMaxNumPlayers(getMaxNumPlayers());
}
// check invariant getNumPlayers() <= getMaxNumPlayers()
if (getNumPlayers() > getMaxNumPlayers()) {
throw new IllegalNumPlayers(getNumPlayers());
}
// check invariant getLeague() != null
if (getLeague() == null) {
throw new IllegalLeague();
}
// check invariant getName() != null
if (getName() == null) {
throw new IllegalName();
}
}
//...
}
```
Figure 10-10 Checking code for removePlayer()