Using Command- Pattern to create an object and add this to an ArrayList

Question

I have a Problem to understand the exercise. What I have to do is:

1. Different users must be able to add and delete a ticket to a ticketsystem (in a List)
2. I have to do this with the Command- Design- Pattern

But I actually don´t know how to do this. I have thought about the following:

Student press the "createTicketForinsideBuildingDamage"- Button

• -> this sets the "executionCommand" to "insideBuildingDamageCommand" and executes it
• -> this creates a "insideBuildingDamage"- class and it asks for the data like date, type, name...
• -> !!!and this has to be added to the Ticketsystemlist automatically!!! but how can I do this?

Or am I completley wrong? I don´t want a solution like full code. But an idea, how I can do this. Thank you

Answer 1

Firstly, I think you should understand how the design pattern works and how the classes interact with each other. You can see an example here https://refactoring.guru/design-patterns/command.

My way of doing it:

Command.java

// concrete commands will implement this interface
// you can also use an abstract class if you want to have certain attributes, such as a TicketSystem
public interface Command { 
    // this method can be set to return something useful instead of void, if needed
    void execute();
}

AddTicketCommand.java

public class AddTicketCommand implements Command {
    // TicketSystem and Ticket attributes

    // constructor that initializes the attributes

    @Override
    public void execute() {
        // add the Ticket to the TicketSystem
    }
}

Invoker.java

public class Invoker {
    private Command command;

    public void setCommand(Command command) {
        this.command = command;
    }

    public void invoke() {
        command.execute();
    }
}

Therefore, when you want to use a certain command, you set it with accordingly. For example: invoker.setCommand(new AddTicketCommand(new TicketSystem(), new Ticket())) and then call it with invoker.invoke().

Hope it helped!