public abstract class ConsoleAction {
	public abstract String getCommand();
	public String checkArgs(String[] args) {
		return null;
	}
	public abstract void execute(String[] args);
}

String ret = doSomething();


if (ret == "Falsche Eingabe") doStuff(1);
if (ret == "Zu große Zahl") doStuff(2);

try {
  doStuff();
} catch (FooException e) {
  bla();
} catch (BarException a) {
  bar();
}

public Person(String name) {
	if(!name.matches("[A-Z][a-z]*")) {
		throw new IllegalArgumentException("Error: Name must not be "+name);
	}
	this.setName(name);
}

void setName(String name) {
   if (null == name) {
       throw new InvalidArgumentException("name");
   }

   this.name = name;
}

bool trySetName(String name) {
    try {
        this.setName(name);
    }
    catch (InvalidArgumentException) {
        this.name = null;
        return false;
    }

    return true;
}

abstract class Unit
{
    public bool IsValid(ICollection<string> errors)
    {
        IEnumerable<string> messages = this.Validate();
        if (!messages.Any())
        {
            return true;
        }

        foreach (string error in messages)
        {
            errors.Add(message);
        }

        return false;
    }

    protected abstract IEnumerable<string> Validate();
}

class Person : Unit
{
    public string Name { get; set; }
    
    protected IEnumerable<string> Validate()
    {
        if (String.IsNullOrEmpty(this.Name))
        {
            yield return "Name darf nicht null oder leer sein.";
        }
    }
}

static void Main(string[] args)
{
    Unit[] units = new Unit[]
    {
        new Person { Name = "Jonas" },
        new Person { Name = null },
        new Person { Name = "" }
    };

    foreach (Unit unit in units)
    {
        List<string> errors = new List<string>();
        if (!unit.IsValid(errors)) 
        {
            foreach (string error in errors)
            {
                Console.WriteLine("Fehler gefunden: {0}", error);
            }
        }
    }
}