What pattern to use with a Strategy Pattern to avoid duplicate code inside Concrete Strategies?

Question

I'm relatively new to design patterns and in the following example I am using what I believe is a Strategy Pattern. However, I am repeating myself inside some, not all, concrete strategies and wondering is there a way to avoid this? Notice how ACommand and CCommand have the same code before doing something unique.

public interface Command 
{
    public boolean execute(CommandSender sender, String[] args);
    public String getName();
    //...
}

public abstract class PlayerCommand implements Command 
{
    protected BukkitPlugin plugin = BukkitPlugin.getInstance();

    private String name;
    //...

    public PlayerCommand(String name) 
    {
        this.name = name;
    }

    public String getName() 
    {
        return this.name;
    }

    //...
}

ACommand

    public class ACommand extends PlayerCommand
    {
        public ACommand()
        {
            super("A");
        }

        public boolean execute(CommandSender sender, String[] args)
        {
            Player player = (Player) sender;
            PlayerInventory inventory = player.getInventory();
            ItemStack itemInHand = inventory.getItemInHand();

            if(itemInHand.getType() != Material.COMPASS)
            {
                sender.sendMessage("You must be holding a phone to use this command");
                return true;
            }

            int id = itemInHand.getDurability();

            MobilePhoneManager phoneManager = plugin.getMobilePhoneManager();       
            boolean isMobilePhone = phoneManager.isMobilePhone(id);

            if(!isMobilePhone)
            {
                sender.sendMessage("You must be holding a mobile phone to use this command");
                return true;
            }

            //DO SOMETHING UNIQUE HERE
        }
}

BCommand

public class BCommand extends PlayerCommand
        {
            public BCommand()
            {
                super("B");
            }

            public boolean execute(CommandSender sender, String[] args)
            {
                //SOMETHING ELSE
            }
    }

CCommand

    public class CCommand extends PlayerCommand
    {
        public CCommand()
        {
            super("C");
        }

        public boolean execute(CommandSender sender, String[] args)
        {
            Player player = (Player) sender;
            PlayerInventory inventory = player.getInventory();
            ItemStack itemInHand = inventory.getItemInHand();

            if(itemInHand.getType() != Material.COMPASS)
            {
                sender.sendMessage("You must be holding a phone to use this command");
                return true;
            }

            int id = itemInHand.getDurability();

            MobilePhoneManager phoneManager = plugin.getMobilePhoneManager();       
            boolean isMobilePhone = phoneManager.isMobilePhone(id);

            if(!isMobilePhone)
            {
                sender.sendMessage("You must be holding a mobile phone to use this command");
                return true;
            }

            //DO SOMETHING UNIQUE HERE
        }
}

This looks like a command pattern. If you see the same line of code all the time factor it out into a function. no need for a new design pattern. — andre, Mar 12 '13 at 20:46

sharakan · Accepted Answer · 2013-03-15T13:17:20.447

8

You could use the template pattern as the basis for a common base class between ACommand and CCommand. The template method in the base class would hold the common code, then call an (abstract) method to doSomethingUnique().

edited Mar 15 '13 at 13:17

answered Mar 12 '13 at 20:47

sharakan

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score 0 · Answer 2 · answered Mar 13 '13 at 05:13

Andre is right on all counts. You are using a Command pattern and you just need to tweak your interface a bit to include some notion of whether the command is currently in a state where it can execute

bool canExecute();
boll canExecute(args)

You usually don't see the execute method return anything though.

HTH,
Berryl

What pattern to use with a Strategy Pattern to avoid duplicate code inside Concrete Strategies?

2 Answers2

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