Lambda Expression

• Java 8 feature

• Anonymous function whose definition is not bound to an identifier

• To replace anonymous inner class

• Only works for FunctionalInterface

• @FunctionalInterface
  interface MyLambda {
    void display(String s);
  }
  
  public class Main {
    public static void main(String[] args) {
      MyLambda m = (s) -> {
        System.out.println("Hello " + s);
      };
      m.display("David");
    }
  }

• Acting as an object

• Local variables referenced from a lambda expression must be final or effectively final (not modified)

• Instance variables can be accessed and modified

• Use cases

  • Runnable
  • Comparator
  • Listener
  • Collections

Very similar to arrow function in JavaScript

Oracle tutorial

• Method references

  • Sometimes, a lambda expression does nothing but call an existing method. In those cases, it's often clearer to refer to the existing method by name

  • Kind	Syntax	Examples
    Reference to a static method	ContainingClass::staticMethodName	Person::compareByAge MethodReferencesExamples::appendStrings
    Reference to an instance method of a particular object	containingObject::instanceMethodName	myComparisonProvider::compareByName myApp::appendStrings2
    Reference to an instance method of an arbitrary object of a particular type	ContainingType::methodName	String::compareToIgnoreCase String::concat
    Reference to a constructor	ClassName::new	HashSet::new