class Stack {
    private final ArrayList<float> backend;
    public void push(float value) {
    }
}

interface Command {
    void Execute(Stack target);
}

class CommandPush implements Command {
    @Override
    public void Execute(Stack target) {
        target.push();
    }
}

private java.util.HashMap<String, Callable<Command>> commandsConstructor;

void prepareCommands() {
    commandsConstructor = new HashMap<>();
    commandsConstructor.put("PUSH", o -> new PushCommand());
}