JavaLambda.java

@FunctionalInterface
interface Printer {
  void print(String value);
}

class TextPrinter implements Printer {
  void print(String value) {
    System.out.println(value); 
  }
}

Printer printer = new TextPrinter();
printer.print("Hi");  // prints out "Hi"

printer = printer::print;
printer.print("Hi");  // also prints out "Hi"

Printer printer = (value) -> {
  System.out.println(value);
}
printer.print("Hi");  // prints out "Hi"

printer = System.out::println;
printer.print("Hi");  // also prints out "Hi"