Part 14 in a Series. ClassToInstanceMap is a specialized Map whose keys are class literals like PizzaPromotion.class or RestockingInformation.class and whose values are instances of those types. It provides a convenient balance between type safety and model flexibility. In some code I wrote recently, I needed to attach…
Part 13 in a Series by Jerome Mourits, Guest blogger... A BiMap is a map that supports an inverse view. If you need to map from key to value and also from value to key, then a BiMap is what you want! Note that the values of a BiMap must…
Part 12 in a Series. Comparators.fromFunction() allows you to create a Comparator based on the properties and attributes of a your business objects. Since the same function is applied to both of the values to compare, this method makes it easier to write a symmetric comparator: Before: public Comparator&…
Part 11 in a Series by Jerome Mourits, Guest blogger... Generics are good, but they can be really wordy! Before: Map<CustomerId, BillingOrderHistory> customerOrderHistoryMap = new HashMap<CustomerId, BillingOrderHistory>();`</pre> ### After: <pre class="prettyprint">`Map<…
Part 10 in a Series by Jerome Mourits, Guest blogger... Join makes it easy to join Strings separated by a delimiter. Before: public class ShoppingList { private List<Item> items = ...; ... public String toString() { StringBuilder stringBuilder = new StringBuilder(); for (Iterator<Item> s = items.iterator(…
Part 9 in a Series by Robert Konigsberg, Guest blogger... Multimap is like a Map, but lets you store multiple values for every key. It turns out this is frequently useful. Consider how often you have had to create, for instance, a Map<K, List<V>>…
Joel Spolsky is generally a great writer, but he didn't do his research for today's post. He claims that with the web, JavaScript is the new assembly language: it's capable but not portable: [...] build a programming language, like C, that’s portable and efficient. It should compile down to “native”…
Part 8 in a Series. Constraints.constrainedList allows you to enforce rules about what can be added to a List instance. By letting the List manage its constraints, your API users get instant feedback if they insert invalid values. It also allows you to expose convenient methods like addAll() and…
Part 7 in a Series. Iterables.concat() combines multiple iterables (such as ArrayList and HashSet) so you can go through multiple collections' elements in a single pass: Before: public boolean orderContains(Product product) { List<LineItem> allLineItems = new ArrayList<LineItem>(); allLineItems.addAll(getPurchasedItems(…
Part 6 in a Series by Robert Konigsberg, Guest blogger... In the first episode, Jesse talked about the Preconditions class. That's not the only mechanism supplied by the Google Collections library for data validation. We're going to look at Objects.nonNull(T) and, by association, Objects.nonNull(T, String). Objects.…
Part 5 in a Series. ImmutableList.copyOf() creates an immutable copy of it's arguments as a List. Wherever your code stores a List parameter, it may need an immutable copy. With the JDK, coping and preventing modification requires two steps. Lists.immutableList simplifies this code: Before: public Directions(Address from,…
Part 4 in a Series. Objects.equal(Object,Object) and Objects.hashCode(Object...) provide built-in null-handling, which makes implementing your own equals() and hashCode() methods easy. Before: public boolean equals(Object o) { if (o instanceof Order) { Order that = (Order)o; return (address != null ? address.equals(that.address) : that.address == null)…
Part 3 in a Series. Comparators.max takes two Comparables and returns the larger of the two. It improves upon the standard approach, which requires both a comparison and a ternary: Before: public Money calculateDeliveryCharge(Order order) { double distanceInKm = Geography.getDistance( storeAddress, order.getAddress()); Money perKm = pricePerKm.times(distanceInKm); _return…
Part 2 in a Series. Iterables.getOnlyElement makes sure your collection or iterable contains exactly one element, and returns that. If it contains 0 or 2+ elements, it throws a RuntimeException. This comes up often in unit tests: Before: public void testWorkSchedule() { workSchedule.scheduleUserOnDuty(jesse, mondayAt430pm, mondayAt1130pm); Set<…
Part 1 in a Series. In this N-part series, I'll demonstrate my favourite APIs from the recently announced Google Collections project. I'll present before and after examples that show how you can use Google Collections to write more concise code. Preconditions provides methods for state validation. It makes input validation…
Yesterday afternoon I had a great technical discussion with Joshua Bloch, a very highly respected API designer. We met to talk about something that's very close to my heart, observable lists. We explored this problem with a whiteboard and some code samples and came up with some interesting observations... 1.…
As of today, beansbinding does a very lightweight approach to observable lists. There's two interfaces, ObservableList.java and ObservableListListener.java. I'm refining a proposal for a more heavyweight approach. In addition to simplified List and Listener interfaces, I add a ListEvent interface and a ListEventBuilder class. Motivation for these interfaces:…
My IM client at work is the Google Talk widget that's built-in to Gmail. It works okay, but it's annoying for typing code snippets into chats. Code snippets require multiple lines of text, but pressing Enter commits the message. How to send a multi-line message? Well today I accidentally discovered…
In the latest rev of beansbinding, the AbstractProperty class is stateful. This means that when you add a listener to an object, the property independently remembers both. For example, suppose your code uses databinding in a dialog: private static final Property<jtextfield,string> textFieldTextProperty = new BeanProperty<…
In a recent post, I described how I implemented the observers for stateless properties. In this follow up I describe how to do observers for chained properties. What's a chained property? Suppose I'd like to bind a combo box to a customer's country. If the Customer bean has a getCountry(…
I've got a simplified Property interface and a mixin that makes the property observable: public interface Property<B,V> { V get(B bean); void set(B bean, V value); } public interface ObservableProperty<B,V> extends Property <B,V>…
I keep seeing this exact same Javadoc being written over and over again: /** * A pizza delivery. * * @author jessewilson */ public class PizzaDelivery { ... /** * Sets the address of this PizzaDelivery. * * @param address the address to set. */ public void setAddress(Address address) { ... } } Naturally, this doc took the code author time to write. He typed…
In complex systems, transparency can sometimes help. In my fake pizzastore application, I've got an API that's used to control whether the Place Order! button is enabled or disabled: public boolean isOrderValid(PizzaOrder pizzaOrder) { if (!geography.isAcceptableAddress(pizzaOrder.getAddress())) { return false; } if (!deliveryRules.isLargeEnoughOrder(pizzaOrder)) { return false; } List<…
Today I found the following interface while doing a code review: interface DeliveryListener { void deliveryFulfilled(Delivery delivery); void deliveriesFulfilled(Set<Delivery> deliveries); } This code offends me because the first interface method is a special case of the second method. Why not just use a singleton list!…
When I bought my HDTV in February, I paid extra for 1080p so I could brag about having a higher resolution than my friends who all have 1080i TVs. But my ability to brag was theoretical until I could plug in a source that produced a 1080p signal. Naturally, that…
In Part 1 and Part 2, I removed several static calls in my pizza program. The services class now benefits from an object-oriented design. Replacing static with non-static methods allows for polymorphism and that helps in testing: public class PizzaServices { private final Oven currentOven; private final Address storeAddress; private final…
Writing APIs is hard. There's several factors to balance and it's difficult to get it right the first time. Fortunately, often we don't! We're not all writing code for the JDK, where bad APIs can never be removed in order to retain strict compatibility. Most of the APIs I write…
Most blogging tools like Blogger include an secret link to the page feed in your published HTML. You can only see it by viewing the HTML source of a blog page: <html> <head> <meta http-equiv="Content-Type" content="…
I've kind of had a love-hate attitude towards the JSR-295 Beansbinding project: love: observable lists in the JDK hate: the observable lists' events are [not fine-grained](http://publicobject.com/2006/06/fine-grained-events-for-performance.html) love: binding in the JDK hate: [it requires EL](http://weblogs.java.net/blog/forax/archive/2007/…
In Part 1, I removed some of the static calls in my pizza program, leaving me with this code. It still has several static calls that interfere with testability: public class PizzaServices { private final Oven currentOven; @Inject public PizzaServices(Oven currentOven) { this.currentOven = currentOven; } public Order createOrder(List<…
In this N-part series, I'm attempting to document some patterns for improving your code with Guice. In each example, I'll start with sample code, explain what I don't like about it, and then show how I clean it up. The bad code They're everywhere! Static utility methods that depend on…
Recently I've seen comments about how language complexity is a Bad Thing that Must Be Avoided. I disagree. The expressiveness of a language influences what you can say with it. This applies to natural languages, programming languages, even programming APIs! When the language gets more complex (by adding new words…
First-class methods (FCM) is a compelling proposal to enhance the Java language so that methods, fields and constructors can have full type-safety. In today's Java, we write this: Method getter = Action.class.getDeclaredMethod("isEnabled", new Class[] { }); Method setter = Action.class.getDeclaredMethod("setEnabled", new Class[] { boolean.class…
We're having a properties discussion over on the beansbinding (JSR-295) mailing list. Here's a recent revision of the API: /** * Models the relationship between two related types, such as * the address of a customer or the size of a List. * * <p>A property is not bound to…
Google Guice uses plain old Java code as the configuration code. For example, here's the code that sets up my fictional pizza store management application: public class PizzaOrdering implements Module { public void configure(Binder binder) { // tell Guice that whenever the code needs an implementation of // my CallInOrderHandler interface, the WebCallInOrderHandler…
Frequently on my team we have a class that gets some of its constructor parameters from the Guice Injector and others from the caller: public class RealPayment implements Payment { public RealPayment( CreditService creditService, // from the [Injector](http://google-guice.googlecode.com/svn/trunk/javadoc/com/google/inject/Injector.html) AuthService authService,…
I pay a cheap annual fee - $97/year - to host publicobject.com, swank.ca and some others at Dreamhost. Today I went to publicobject.com and the site was down. I checked the usual suspects: did I let my domain registration expire? is DNS set up correctly by…
I have an enumerated type, and it's possible that I'll be adding more values in the future. public enum Office { CALGARY, REGINA, TORONTO, BERLIN; }`</pre> Somewhere in the code, I switch on this type: <pre>`public CurrencyCode getCurrencyForPayingEmployees(Office office) { switch(office) { case CALGARY: case REGINA:…
Engadget's a fun site, but their use of Flash means I can't use my mousewheel to scroll through their site. Invasive ads are bad.…
Today Cory Doctorow gave a tech talk to my company. He talked about how DRM is a wasted effort and how it's important that we don't bake-it-in to the technology that we build. So this evening I decided to look for Cory's Overclocked book in audiobook form. Unfortunately, I couldn't…
This is a fun problem - how would you implement it? public interface IndexedValues<V> { /** * Inserts the specified value at the specified index. The same * value may be inserted several times in the same collection. */ void insert(int index, V value); /** * Returns the index of the…
I recently subscribed to Simply Audiobooks, which is a Netflix-like service that rents books-on-CD through the mail. I listen to them unabridged so each book spans several CDs - 12 CDs for a single book is typical. Unfortunately, iTunes doesn't handle Audiobooks-from-CD nearly as well as it handles music or…
Details on our Glazed Lists tech session: Sexy Models! An API for Declarative Data Models on the Desktop Session TS-3057, desktop track Friday May 11 at 14:50 in Hall E - 135 We're planning on writing code live during the session to show off how productive Glazed Lists is.…
For the poker game I'm not writing, I wrote a Comparator to rank the player's hands. Now to write a unit tests for that Comparator. Generally I find that it's hard to write test cases for Comparators. You end up having to puzzle over whether to use < 0…
Some applications don't use the built-in print dialog on Mac OS X, which usually means no PDF printing. Fortunately, some kind soul has created a PDF printer that is easily installed on Mac OS X. Its mechanics are similar to PDF 995 for Windows: install the virtual printer print a…
My Mac's filesystem is case-insensitive. It thinks Foo and foo are the same file. Subversion's filesystem is case-sensitive. It thinks Foo and foo are different files. As you can imagine, this mismatch has hilarious consequences. If your repository contains a directory with both Foo and foo, then svn crashes hard…
Today's update is pretty sparse - I cleaned up the new intersect & union features so that you can kick off a new query to intersect and union against. I also drew up some custom icons for union and intersection. My next tasks include a lot of polishing: making the…
Charles is an amazing tool that every web developer should have in their toolchest. It records the HTTP conversations between your browser and the web and lets you analyze them. It can even record HTTPS conversations and remove the encryption. Some questions that Charles will quickly answer: what cookies are…
Today's update of CodeSearch-Plugin allows you to intersect the results of one query with another query. This allows you to search for code that contains both spline and Graphics2D, neither of which is particularly useful on its own. I've also fixed the preflight dialog's handling of ENTER etc., which was…
The newest CodeSearch-Plugin remembers what you searched for last time (including file-types & case-sensitivity), so you can search for it again. Unfortunately, this version has an unfortunate bug - when you change and then tab out of any of the text fields, it tends to kick off your query early.…