Java 9

• 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
• ifPresentOrElse
• or

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

• Optional can be converted into the stream really easily.

• 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:

  • module-info.java

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

• 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