Java. How to replace an if-else block with polymorphism?

Question

I have here such a code I was given the task of breaking the method into classes so that polymorphism would be used. Help a good idea what can be done here?

private void start() { System.out.println("Помощь: \"h\""); ArrayList<String> target = null; String command; try (Scanner scanner = new Scanner(System.in)) { command = scanner.nextLine(); while (!"q".equals(command)) { if ("-f".equals(command)) { // можно сделать System.out.println("Введите полное имя директории для поиска в формате \"absolute path.../dir\":"); Dir dir = new Dir(scanner.nextLine()); System.out.println("Введите имя файла для поиска:"); target = dir.searchByName(scanner.nextLine()); target.forEach(System.out::println); } else if ("-r".equals(command)) { System.out.println("Введите полное имя директории для поиска в формате \"absolute path.../dir\":"); Dir dir = new Dir(scanner.nextLine()); System.out.println("Введите часть имени файла для поиска:"); target = dir.searchRegExp(scanner.nextLine()); System.out.println("Найдено:"); target.forEach(System.out::println); } else if ("-o".equals(command)) { if (target != null) { System.out.println("Введите полное имя директории куда сохранить файл в формате \"absolute path.../dir/\":"); String path = scanner.nextLine(); System.out.println("Введите имя файла в формате \"file.extension\":"); String name = scanner.nextLine(); // получаем каталог куда сохранять if (this.exist(path, name)) { this.write(target, path + name); } else { System.out.println("Действие не возможно."); } } } else if ("h".equals(command)) { printManual(); } else { System.err.println("Неизвестная команда."); printManual(); } command = scanner.nextLine(); } } }

Or maybe it would be easier to look at the design pattern of the Команда and make it?
Are you sure that this needs to be replaced by polymorphism?

Artem Konovalov Artem Konovalov 13.6k 14 36 · Accepted Answer · 2016-12-15T19:46:31

You need to declare several classes and one interface. Further, in a while go over the collection of objects implementing this class, compare names and, if they match, call the invoke method

 public interface Command{ String getName(); void invoke(Scanner scanner); } public class FirstCommand implements Command { public String getName(){ return "-f"; } public void invoke(Scanner scanner){ // можно сделать System.out.println("Введите полное имя директории для поиска в формате \"absolute path.../dir\":"); Dir dir = new Dir(scanner.nextLine()); System.out.println("Введите имя файла для поиска:"); ArrayList<String> target = dir.searchByName(scanner.nextLine()); target.forEach(System.out::println); } }

The flag will come to me from the console, for example, "-f" as in the example, and then it will still get if ("- f". Equals (and it went off ... Or did I misunderstand something?
create a while before loop while Collection <Command> commands, and run over it when you receive a new command, pulling the getName method, if there is a match, then invoke invoke, otherwise go to the next element

Java. How to replace an if-else block with polymorphism?

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