Core Java. Лекция 8

public interface ActionListener {
  void actionPerformed(ActionEvent event);
}

// ----использование----
String text = ...
new Timer(1000, new ActionListener(){
  @Override
  public void actionPerformed(ActionEvent e) {
    ... //'text' var is available here
    }
  });

String[] friends = {"Peter", "Paul", "Mary"};

Arrays.sort(friends,
  new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
      return o1.length() - o2.length();
  }
});

File[] hiddenFiles = new File(".").listFiles(
  new FileFilter() {
    public boolean accept(File file) {
      return file.isHidden();
    }
  }
);

//single-line
(String first, String second) ->
  first.length() - second.length()

//multi-line with int return
(String first, String second) -> {
  if (first.length() < second.length()) return -1;
  else if (first.length() > second.length()) return 1;
  else return 0;
}

//no-arg, void return
() -> System.out.println("Hello!");

//Типы аргументов лямбд указывать не надо: type inference!
ActionListener = e -> {...}
Comparator<String> c = (s1, s2) -> s1.length() - s2.length();

final List<String> list = ...

//Predicate.test возвращает boolean
Predicate<String> p = s -> list.add(s);

//Consumer.accept возвращает void!
Consumer<String> c = s -> list.add(s);

//не скомпилируется
Object o = ()->{};

//Скомпилируется!
Runnable r = ()->{};

//Тоже скомпилируется
Object o = (Runnable) ()->{};

void repeatMessage(String text, int delay) {
  ActionListener  listener = event -> {
    //переменная text доступна внутри лямбды!
    System.out.println(text);
  }
  new Timer(delay, listener).start();

}

int start = ...

for (int i = 0; i < count; i++) {
  ActionListener linstener = event -> {
    start--; //ERROR: Can't mutate captured value

    //ERROR: Cannot refer to changing i
    System.out.println(i);
  }
}

obj = null;

//NPE только в момент запуска лямбды!!
//obj должен быть effectively final!
doSmth(x -> obj.method(x));

//NPE здесь и сейчас
//obj не обязан быть effectively final
doSmth(obj::method)

//Да ладно, разве трудно на null проверить??
Objects.isNull(Object obj)...
Objects.nonNull(Object ob)...


list.removeIf(Objects::isNull);

stream.filter(Objects::nonNull)...

Consumer<String> foo = ...
List<String> list = ...

//Составной консьюмер, отправляющий
//объект сначала в первый, потом во второй
Consumer<String> bar = foo.andThen(list::add);

Predicate<T> a = ...
Predicate<T> b = ...

a.and(b).negate(); // ! (a(x) & b(x))

//Двуместный предикат (x,y)-> Objects.equals(x, y)
Objects::equals

//Одноместный предикат y -> Objects.equals(x, y)
Predicate.isEqual(x)

V computeIfAbsent(K key,
  Function<? super K, ? extends V> mappingFunction)

V computeIfPresent(K key,
  BiFunction<? super K, ? super V, ? extends V> remappingFunction)

V compute(K key,
  BiFunction<? super K, ? super V, ? extends V> remappingFunction)

V merge(K key, V value,
  BiFunction<? super V, ? super V, ? extends V> remappingFunction)

@AllArgsConstructor
public class Person {
    @Getter
    private final String firstName;
    @Getter
    private final String lastName;
}
List<Person> people = new ArrayList<>();

//НЕ ПИШИТЕ ВЕСЬ ЭТОТ КОШМАР
Collections.sort(people,
  (p1, p2) -> {
    int result = p1.getFirstName().compareTo(p2.getFirstName());
    if (result == 0) {
      result = p2.getLastName().compareTo(p2.getLastName());
    }
    return result;
  }
);

Collections.sort(people,
  Comparator
    .comparing(Person::getLastName)
    .thenComparing(Person::getFirstName));
);

Comparator.comparing(keyExtractor, keyComparator)
Comparator.comparingInt/Double(...)
Comparator.reversed()
Comparator.nullsFirst/nullsLast(Comparator c)

jdbc:sqlserver://172.16.1.114:52836;databaseName=celesta

jdbc:postgresql://127.0.0.1:5432/celesta

jdbc:oracle:thin:192.168.110.128:1521:XE

jdbc:derby://localhost:1527/corejava;create=true

try (Connection conn = dataSource.getConnection();
     Statement stmt = conn.createStatement()){

  ResultSet result = stmt.executeQuery("select name from speaker");

  while (result.next()) {

      System.out.println(result.getString("name"));

  }
}

String connString = "jdbc:postgresql://127.0.0.1:5432/celesta"
Connection conn = DriverManager.getConnection(connString);

DataSource connectionPool = ...
try (Connection conn = connectionPool.getConnection()) {
    ...
}

int confId = ...
try (PreparedStatement stmt =
  conn.prepareStatement(
    "select name from talk where conferenceid = ?")) {
  //устанавливаем значение параметра
  //индексация с единицы!!
  stmt.setInt(1, confId);

  ResultSet result = stmt.executeQuery();
  while (result.next()) {
      System.out.println(result.getString("name"));
  }

}

sql = "SELECT * FROM users WHERE name = '" + userName + "'"

userName = "' OR '1'='1"

userName = "a';DROP TABLE users;"

//... и много другой гадости