Java 8 cheatsheet

In

Functional interfaces

  • static: behaves like final methods
  • default: are similar to abstract methods: “default behaviour, but it can be overriden”
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public interface Vehicle{
    static String producer() {
        return "N&F Vehicles";
    }
    default String getOverview() {
        return "ATV made by " + producer();
    }
}

Stream API

  • Reference to static methods
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// with lambdas
boolean isReal = list.stream().anyMatch(u -> User.isRealUser(u));
// avoiding lambdas
boolean isReal = list.stream().anyMatch(User::isRealUser);
  • Reference to an instance method
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long count = list.stream().filter(String::isEmpty).count();
  • Reference to a constructor
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Stream<User> stream = list.stream().map(User::new);

Optional as nullpointer protection

  • Definition

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    Optional<String> optional = Optional.of("value");

  • Simplifying conditionals

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    // conditional
    List<String> listOpt = list != null ? list : new ArrayList<>();
    // optional
    List<String> listOpt = getList().orElse(new ArrayList<>());
    List<String> listOpt = getList().orElseGet(ArrayList::new);

  • Handling nullables with default values

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    Optional<OptionalUser> optionalUser = Optional.ofNullable(getOptionalUser());
    String result = optionalUser
        .flatMap(OptionalUser::getAddress)
        .flatMap(OptionalAddress::getStreet)
        .orElse("not specified");

  • Handling nullable exceptions

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    String value = null;
    Optional<String> valueOpt = Optional.ofNullable(value);
    String result = valueOpt.orElseThrow(CustomException::new).toUpperCase();