Changes_in_Java_9.md

• Interface private methods
  • you can write helpers for more classes, but they won't be public

interface Util {
  default int getNumber() { return helper(); }
  private int helper() { return 4; }
}

• Effectively final in try-with-resources
  • use AutoCloseable for a class that is used in try-catch when we leave the scope on try-catch. Then the close method is automatically called. (can be dangerous!)

class Resource implements AutoCloseable {
  public void foo() { ... };
  public void close() { ... };
}

public static Sample {
  Resource resource = new Resource();
  try(resource) {
    resource.method();
}

• No _

  • underscore is not available as a name of a variable.

• Iterate above IntStream

  • takeWhile
  • dropWhile

IntStream.iterate(0, i -> i + 2)
    .takeWhile(i -> i <= 5)
    .forEach(System.out::println);

• Optional
  • Optional can be converted into the stream really easily.
  • ifPresentOrElse
  • or

Optional<Integer> first =
number.stream()
  .filter(e -> e > 50)
  .findFirst()
  .or(() -> Optional.of(77));

• REPL

• Modularization

  • the problem:
    • big jars
    • lack of clarity on dependencies
    • public is too open
    • class path -> fail late or early
    • reflection can be used when module is opened or module opens a package
  • JDK Modularized
    • module: collection of data with name, requires (only modules), exports (only packages)
    • every JDK module depends on java.base
    • public is not the same anymore
  • Create module:
    • javac ... => compile the code
    • jar ... => jar all *.class
    • jar -f *.jar -d => says what is in jar file
    • java -p [module_path] -m module/class => run the code
    • module-info.java

module com.name {
  requires java.base; 
  requires transitive com.for.all;
  exports com.name.best;
}