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    Lambdaj

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    sriramn78
    Lambdaj is a library that provides a domain specific language (DSL) for manipulating Java collections without using loops. It allows collections to be treated as single objects and methods to be invoked on all collection elements. Key features include forEach to invoke methods on all elements and on to define method references in a statically typed way. Several examples demonstrate converting iterative code to the lambdaj equivalent, showing performance improvements of over 5x on average. Known limitations include issues with null/empty collections and final classes.

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    Lambdaj

    Uploaded by

    sriramn78
    83 views21 pages
    Lambdaj is a library that provides a domain specific language (DSL) for manipulating Java collections without using loops. It allows collections to be treated as single objects and methods to be invoked on all collection elements. Key features include forEach to invoke methods on all elements and on to define method references in a statically typed way. Several examples demonstrate converting iterative code to the lambdaj equivalent, showing performance improvements of over 5x on average. Known limitations include issues with null/empty collections and final classes.

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    lambdaj

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    Lambdaj is a library that provides a domain specific language (DSL) for manipulating Java collections without using loops. It allows collections to be treated as single objects and methods to be invoked on all collection elements. Key features include forEach to invoke methods on all elements and on to define method references in a statically typed way. Several examples demonstrate converting iterative code to the lambdaj equivalent, showing performance improvements of over 5x on average. Known limitations include issues with null/empty collections and final classes.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    83 views21 pages

    Lambdaj

    Uploaded by

    sriramn78
    Lambdaj is a library that provides a domain specific language (DSL) for manipulating Java collections without using loops. It allows collections to be treated as single objects and methods to be invoked on all collection elements. Key features include forEach to invoke methods on all elements and on to define method references in a statically typed way. Several examples demonstrate converting iterative code to the lambdaj equivalent, showing performance improvements of over 5x on average. Known limitations include issues with null/empty collections and final classes.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 21

    ambdaj

    An internal DSL to manipulate collections without loops


    by Mario Fusco mario@exmachina.ch

    What is lambdaj for?


    It provides a DSL to manipulate collections in a pseudo-functional and statically typed way. It eliminates the burden to write (often poorly readable) loops while iterating over collections. It allows to iterate collections in order to: convert filter aggregate index

    group
    sort

    extract

    How does lambdaj work?


    lambdaj is a thread safe library of static methods based on 2 main features: treat a collection as it was a single object by allowing to propagate a single method invocation to all the objects in the collection forEach(personsInFamily).setLastName("Fusco"); allow to define a pointer to a java method in a statically typed way sort(persons, on(Person.class).getAge());

    Thats all you need to know to start using lambdaj

    It sounds easy, isnt it?

    If you dont believe me lets see some

    EXAMPLEs & DEMOs

    The Demo Data Model

    Print all cars brands


    Iterative version:
    StringBuilder sb = new StringBuilder(); for (Car car : db.getCars()) sb.append(car.getBrand()).append(", "); String brands = sb.toString().substring(0, sb.length()-2);

    lambdaj version:
    String brands = joinFrom(db.getCars()).getBrand();

    Select all sales of a Ferrari


    Iterative version:
    List<Sale> salesOfAFerrari = new ArrayList<Sale>(); for (Sale sale : sales) { if (sale.getCar().getBrand().equals("Ferrari")) salesOfAFerrari.add(sale); }

    lambdaj version:
    List<Sale> salesOfAFerrari = select(sales, having(on(Sale.class).getCar().getBrand(),equalTo("Ferrari")));

    Find buys of youngest person


    Iterative version:
    Person youngest = null; for (Person person : persons) if (youngest == null || person.getAge() < youngest.getAge()) youngest = person; List<Sale> buys = new ArrayList<Sale>(); for (Sale sale : sales) if (sale.getBuyer().equals(youngest)) buys.add(sale);

    lambdaj version:
    List<Sale> sales = select(sales,having(on(Sale.class).getBuyer(), equalTo(selectMin(persons, on(Person.class).getAge()))));

    Find most costly sale


    Iterative version:
    double maxCost = 0.0; for (Sale sale : sales) { double cost = sale.getCost(); if (cost > maxCost) maxCost = cost; }

    lambdaj version:
    Sol. 1 -> double maxCost = max(sales, on(Sale.class).getCost()); Sol. 2 -> double maxCost = maxFrom(sales).getCost();

    Sum costs where both are males


    Iterative version:
    double sum = 0.0; for (Sale sale : sales) { if (sale.getBuyer().isMale() && sale.getSeller().isMale()) sum += sale.getCost(); }

    lambdaj version:
    double sum = sumFrom(select(sales, having(on(Sale.class).getBuyer().isMale()).and( having(on(Sale.class).getSeller().isMale())))).getCost();

    Find age of youngest who bought for more than 50,000


    Iterative version:
    int age = Integer.MAX_VALUE; for (Sale sale : sales) { if (sale.getCost() > 50000.00) { int buyerAge = sale.getBuyer().getAge(); if (buyerAge < age) age = buyerAge; } }

    lambdaj version:
    int age = min(forEach(select(sales, having(on(Sale.class).getCost(), greaterThan(50000.00)))) .getBuyer(), on(Person.class).getAge());

    Sort sales by cost


    Iterative version:
    List<Sale> sortedSales = new ArrayList<Sale>(sales); Collections.sort(sortedSales, new Comparator<Sale>() { public int compare(Sale s1, Sale s2) { return Double.valueOf(s1.getCost()).compareTo(s2.getCost()); } });

    lambdaj version:
    List<Sale> sortedSales = sort(sales, on(Sale.class).getCost());

    Extract cars original cost


    Iterative version:
    List<Double> costs = new ArrayList<Double>(); for (Car car : cars) costs.add(car.getOriginalValue());

    lambdaj version:
    List<Double> costs = extract(cars, on(Car.class).getOriginalValue());

    Index cars by brand


    Iterative version:
    Map<String, Car> carsByBrand = new HashMap<String, Car>(); for (Car car : db.getCars()) carsByBrand.put(car.getBrand(), car);

    lambdaj version:
    Map<String, Car> carsByBrand = index(cars, on(Car.class).getBrand());

    Group sales by buyers and sellers


    (iterative version)
    Map<Person,Map<Person,Sale>> map = new HashMap<Person,Map<Person,Sale>>(); for (Sale sale : sales) { Person buyer = sale.getBuyer(); Map<Person, Sale> buyerMap = map.get(buyer); if (buyerMap == null) { buyerMap = new HashMap<Person, Sale>(); map.put(buyer, buyerMap); } buyerMap.put(sale.getSeller(), sale); } Person youngest = null; Person oldest = null; for (Person person : persons) { if (youngest == null || person.getAge() < youngest.getAge()) youngest = person; if (oldest == null || person.getAge() > oldest.getAge()) oldest = person; } Sale saleFromYoungestToOldest = map.get(youngest).get(oldest);

    Group sales by buyers and sellers


    (lambdaj version)
    Group<Sale> group = group(sales, by(on(Sale.class).getBuyer()),by(on(Sale.class).getSeller())); Person youngest = selectMin(persons, on(Person.class).getAge()); Person oldest = selectMax(persons, on(Person.class).getAge()); Sale sale = group.findGroup(youngest).find(oldest).get(0);

    Find most bought car


    (iterative version)
    Map<Car, Integer> carsBought = new HashMap<Car, Integer>(); for (Sale sale : sales) { Car car = sale.getCar(); Integer boughtTimes = carsBought.get(car); carsBought.put(car, boughtTimes == null ? 1 : boughtTimes+1); } Car mostBoughtCarIterative = null; int boughtTimesIterative = 0; for (Entry<Car, Integer> entry : carsBought.entrySet()) { if (entry.getValue() > boughtTimesIterative) { mostBoughtCarIterative = entry.getKey(); boughtTimesIterative = entry.getValue(); } }

    Find most bought car


    (lambdaj version)
    Group<Sale> group = selectMax( group(sales, by(on(Sale.class).getCar())).subgroups(), on(Group.class).getSize()); Car mostBoughtCar = group.findAll().get(0).getCar(); int boughtTimes = group.getSize();

    Performance analysis
    Minimum, maximum and average duration in milliseconds of 10 runs of 100,000 iterations of the former examples
    PrintAllBrands FindAllSalesOfAFerrari FindAllBuysOfYoungestPerson FindMostCostlySaleValue SumCostsWhereBothActorsAreAMale AgeOfYoungestBuyerForMoreThan50K SortSalesByCost ExtractCarsOriginalCost IndexCarsByBrand GroupSalesByBuyersAndSellers FindMostBoughtCar min 656 688 13.485 531 843 12.890 3.250 328 469 23.657 8.296 iterative max 1.016 766 14.969 547 875 13.063 3.500 344 500 24.079 8.484 avg 769 761 14.757 544 859 12.965 3.421 333 485 23.835 8.395 min 5.812 6.172 18.953 3.546 10.828 24.860 21.953 1.218 1.484 36.375 28.421 lambdaj max 6.266 6.297 19.375 3.579 11.141 25.234 22.312 1.250 1.531 37.046 28.859 avg 5.905 6.214 19.124 3.564 11.021 25.089 22.080 1.228 1.511 36.686 28.614 ratio 7,679 8,166 1,296 6,551 12,830 1,935 6,454 3,688 3,115 1,539 3,408

    Average ratio =

    5,151

    Known limitations
    lambdaj cannot Lack of reified generics infer the actual type to be returned when a null or empty collection is passed to forEach()
    List<Person> persons = new ArrayList<Person>(); forEach(persons).setLastName("Fusco"); Exception

    Impossibility to proxy a final class the on() construct cannot register an invocation after a final Class is met
    List<Person> sortedByNamePersons = sort(persons, on(Person.class).getName().toLowerCase()); Exception

    Check out lambdaj at:

    code.google.com/p/lambdaj
    Thank you

    Mario Fusco

    mario@exmachina.ch

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