command pattern variable number of parameters in execute method

[oll3i]

i want to write a bank account programme and use a command pattern where execute method has variable number of parameters.


[code]
public interface Command {
public abstract void execute (String ... s);
}
[code]
how do i get the parameters passed to that method?
when is the execute method called?

[JosAH]

i want to write a bank account programme and use a command pattern where execute method has variable number of parameters.

public interface Command {
     public abstract void execute (String ...  s);
}
 

how do i get the parameters passed to that method?
when is the execute method called?

You're in trouble here: other objects are not supposed to know anything at all
about an actual implementation of the Command interface so they don't know
how many Strings to pass to that particular implementation. All that the other
objects know is that they can pass zero or more Strings to your Command,
that's all. I think you have to go back to the drawing board for a bit more time.

kind regards,

Jos

[oll3i]

so i'm not on a good path?
what's wrong with my Command?

[JosAH]

so i'm not on a good path?
what's wrong with my Command?

That's what I wrote in my previous reply, but maybe things are not so bad.
What do these Strings mean? Can every Command take a variable number
of Strings or are the number of Strings depending on *which* Command is
to be executed?

kind regards,

Jos

[oll3i]

the number of Strings is depending on which Command is
to be executed i think ?

 
public class WplacnaKonto implements Command { 
// class for putting the money into account
private Konto konto = new Konto();  // Account account = new Account();
 
public WplacnaKonto(Konto k){
    konto=k;    
}
 
 
public void execute(String ... rozkaz){
    double suma = Double.valueOf(rozkaz[0].trim()).doubleValue();
     konto.wplata(suma); //account put the money  into account
}
 
}
 

this is a class responsible for putting the money into the account
i was following the example from this tutorial
http://www.javaworld.com/javaworld/j...68.html?page=1

kind regards

[JosAH]

the number of Strings is depending on which Command is
to be executed i think ?

Then there's trouble ahead; suppose you have three different commands: A, B
and C all implementing your Command interface. Command A needs 2 Strings,
Command B needs 1 String and Command C needs 4 Strings. Your other
objects are not supposed to know which Command they're dealing with. How
should they know how many Strings to pass to a Command?

kind regards,

Jos

[oll3i]

uups ... every Command can take a variable number
of Strings

public void execute(String ... rozkaz){
double suma = Double.valueOf(rozkaz[0].trim()).doubleValue();
konto.wplata(suma);
}



putintoaccount.execute("100.00");
displayhistoryofaccounts.execute("3810209876543456 ","3810204455667876");

and i dont know if am doing it right ?

[JosAH]

uups ... every Command can take a variable number
of Strings

public void execute(String ... rozkaz){
double suma = Double.valueOf(rozkaz[0].trim()).doubleValue();
konto.wplata(suma);
}



putintoaccount.execute("100.00");
displayhistoryofaccounts.execute("3810209876543456 ","3810204455667876");

and i dont know if am doing it right ?

Not really because your scenario allows me to do this:

putintoaccount.execute("foo", "bar", "baz");
displayhistoryofaccounts.execute("100.00", "-42", "Fido the Poodle");

In other words: I don't know to which Command I'm talking and I don't know
what to put as parameter values. All I know is that I'm talking to a Command
that takes zero or more Strings as its parameter list.

kind regards,

Jos

[oll3i]

so what would you suggest me to do?

[oll3i]

should i change my command execute method?

[JosAH]

should i change my command execute method?

Something like that; I don't think you want a Command pattern here, i.e. you
want to say different things to different objects and you want to know about
the difference of those objects. For an account thing you want to say: gimme
all the account details and withdraw or deposit some money. Make those
different methods. IMHO you want an Account interface with different methods,
one for each purpose. Squeezing everything into one method is not the way to go.

kind regards,

Jos

[oll3i]

but my account class has methods for deposit and withdrawal then i created a class responsible for depositing and call account.deposit(sum) from that class execute method

 
public class Deposit implements Command {
private Account account = new Account();
 
public Deposit(Account a){
    account=a;    
}
 
 
public void execute(String... rozkaz){
    double sum = Double.valueOf(rozkaz[0].trim()).doubleValue();
 
    account.deposit(sum);
}
 
}
 
 

and another class responsible for withdrawal
i call account.withdrawal(sum) from that class execute method

public class Withdrawal implements Command {
private Account account= new Account();
 
public Withdrawal( Account a){
    account=a;    
}
 
public void execute(String ... rozkaz){
    double sum= Double.valueOf(rozkaz[0].trim()).doubleValue();
     account.withdrawal(sum);
}
}
 
 
 

and then i created a class responsible for displaying the history of the accounts
that was displayhistoryofaccounts.execute("number of the account","number of the account") but you said that's not the way to go

[JosAH]

and then i created a class responsible for displaying the history of the accounts
that was displayhistoryofaccounts.execute("number of the account","number of the account") but you said that's not the way to go

But why do you want to implement a Command class for all those different
actions? Those different actions all take a different number of parameters,
even different types of parameters.

Why hide that fact by using a varargs String ... parameter list. It doesn't buy
you anything here. If I want to withdraw money from an account I know what
to do: tell the Account to withdraw some money; same with the deposit action.

If you really want to hide those details you should encapsulate those details
in the Command implementing classes; it'll be quite a bit of overhead:

public class Withdrawer implements Command {
   private Account a;
   private double amount;
   public Withdrawer(Account a, double amount) {
      this.a= a;
      this.amount= amount;
   }
   // interface implementation
   public void execute() {
      a.withdraw(amount);
   }
}

public class Depositer implements Command {
   private Account a;
   private double amount;
   public Depositer(Account a, double amount) {
      this.a= a;
      this.amount= amount;
   }
   // interface implementation
   public void execute() {
      a.deposit(amount);
   }
}

public interface Command {
   public void execute();
}

Only then you have abstracted away what actually has been done to accounts
but at quite a high cost, i.e. for every account action you have to create a new
object with the Account and possibly some money value.

Listing all accounts does fit too in that scenario. Possibly a static method in the
Account class can do the real job, delegated by another Command class.

kind regards,

Jos

[oll3i]

but the requirement is to write it with execute method with variable number of parameters

[JosAH]

but the requirement is to write it with execute method with variable number of parameters

Well go for it then but I'd say: shoot those requirements and the moron who
made them up. The one who makes up requirements is usually not the one
who has to implement the inconsistent, ambiguous, incomplete, not well
thought out rubbish and waste of precious bytes and trees.

Since when do requirement defining business analysts prescribe the patterns
to be used anyway?

kind regards,

Jos ;-)