What data structure provides the highest speed with…

The Command pattern often uses data structures that provide quick access by key or the ability to preserve execution order.

HashMap<String, Command>: Provides quick access to commands by their string names.

// Command interface
interface Command {
    void execute();
}

// Command implementation
class LightOnCommand implements Command {
    Light light;

    public LightOnCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.on();
    }
}

// Command mapping
Map<String, Command> commands = new HashMap<>();
commands.put("LightOn", new LightOnCommand(new Light()));

// Execute command by name
Command command = commands.get("LightOn");
if (command != null) {
    command.execute();
}

LinkedList<Command>: Can be used to organize a queue of commands, allowing easy addition and execution of commands in the order they were added.

// Command interface
interface Command {
    void execute();
}

// Command queue
Queue<Command> commandQueue = new LinkedList<>();
commandQueue.add(new LightOnCommand(new Light()));
commandQueue.add(new LightOffCommand(new Light()));

// Execute commands from the queue
while (!commandQueue.isEmpty()) {
    commandQueue.poll().execute();
}

The fastest way to work with the Command pattern when accessing by command name is provided by HashMap (average O(1) for get and put). If execution order is important or undo functionality is needed, LinkedList (used as a stack or queue) is suitable.

Replacing the Command pattern in certain scenarios can be:

Simple method calls: If the execution logic is trivial and does not require abstraction, a separate command class is not necessary.

Using functional interfaces (Java 8+): Instead of creating a separate class for each command, lambda expressions or method references can be used to represent commands.

// Using functional interface
@FunctionalInterface
interface Executable {
    void run();
}

// Storing commands in a map using lambdas
Map<String, Executable> commands = new HashMap<>();
commands.put("PrintMessage", () -> System.out.println("Hello from lambda!"));

// Execute command
Executable command = commands.get("PrintMessage");
if (command != null) {
    command.run();
}

This reduces boilerplate code but can complicate undo operations.

Using flags or parameters: In simple cases, when the number of actions is limited, flags or parameters can be passed to a single method that decides which logic to execute.
Using DSL (Domain Specific Language): For complex systems with many commands and variations, a domain-specific language can be developed to describe and execute commands.

What data structure provides the highest speed with the Command pattern, and what can replace this pattern?