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  • Using runtime generic type reflection to build a smarter DAO

    - by kerry
    Have you ever wished you could get the runtime type of your generic class? I wonder why they didn’t put this in the language. It is possible, however, with reflection: Consider a data access object (DAO) (note: I had to use brackets b/c the arrows were messing with wordpress): public interface Identifiable { public Long getId(); } public interface Dao { public T findById(Long id); public void save(T obj); public void delete(T obj); } Using reflection, we can create a DAO implementation base class, HibernateDao, that will work for any object: import java.lang.reflect.Field; import java.lang.reflect.ParameterizedType; public class HibernateDao implements Dao { private final Class clazz; public HibernateDao(Session session) { // the magic ParameterizedType parameterizedType = (ParameterizedType) clazz.getGenericSuperclass(); return (Class) parameterizedType.getActualTypeArguments()[0]; } public T findById(Long id) { return session.get(clazz, id); } public void save(T obj) { session.saveOrUpdate(obj); } public void delete(T obj) { session.delete(obj); } } Then, all we have to do is extend from the class: public class BookDaoHibernateImpl extends HibernateDao { }

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  • Google I/O 2012 - Writing Polished Apps that have Deep Integration into the Google Drive UI

    Google I/O 2012 - Writing Polished Apps that have Deep Integration into the Google Drive UI Mike Procopio, Steve Bazyl We'll go through how to implement complete Drive apps. This is not an introduction to Drive apps, but rather how to build your product into Google Drive, and ensure that the experience is seamless for a user. We will also discuss how to effectively distribute your app in the Chrome Web Store. The example app built in this talk will demonstrate an example use case, but otherwise be production-ready. For all I/O 2012 sessions, go to developers.google.com From: GoogleDevelopers Views: 829 5 ratings Time: 50:59 More in Science & Technology

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  • Naming your unit tests

    - by kerry
    When you create a test for your class, what kind of naming convention do you use for the tests? How thorough are your tests? I have lately switched from the conventional camel case test names to lower case letters with underscores. I have found this increases the readability and causes me to write better tests. A simple utility class: public class ArrayUtils { public static T[] gimmeASlice(T[] anArray, Integer start, Integer end) { // implementation (feeling lazy today) } } I have seen some people who would write a test like this: public class ArrayUtilsTest { @Test public void testGimmeASliceMethod() { // do some tests } } A more thorough and readable test would be: public class ArrayUtilsTest { @Test public void gimmeASlice_returns_appropriate_slice() { // ... } @Test public void gimmeASlice_throws_NullPointerException_when_passed_null() { // ... } @Test public void gimmeASlice_returns_end_of_array_when_slice_is_partly_out_of_bounds() { // ... } @Test public void gimmeASlice_returns_empty_array_when_slice_is_completely_out_of_bounds() { // ... } } Looking at this test, you have no doubt what the method is supposed to do. And, when one fails, you will know exactly what the issue is.

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  • GDD-BR 2010 [1G] Android: Building High-Performance Applications

    GDD-BR 2010 [1G] Android: Building High-Performance Applications Speaker: Tim Bray Track: Android Time: G [16:30 - 17:15] Room: 1 Level: 151 Build Android applications that are smooth, fast, responsive, and a pleasure to use. Also, learn about the tools and techniques we use to track down and fix performance problems. From: GoogleDevelopers Views: 20 0 ratings Time: 33:34 More in Science & Technology

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  • Optimizing a thread safe Java NIO / Serialization / FIFO Queue [migrated]

    - by trialcodr
    I've written a thread safe, persistent FIFO for Serializable items. The reason for reinventing the wheel is that we simply can't afford any third party dependencies in this project and want to keep this really simple. The problem is it isn't fast enough. Most of it is undoubtedly due to reading and writing directly to disk but I think we should be able to squeeze a bit more out of it anyway. Any ideas on how to improve the performance of the 'take'- and 'add'-methods? /** * <code>DiskQueue</code> Persistent, thread safe FIFO queue for * <code>Serializable</code> items. */ public class DiskQueue<ItemT extends Serializable> { public static final int EMPTY_OFFS = -1; public static final int LONG_SIZE = 8; public static final int HEADER_SIZE = LONG_SIZE * 2; private InputStream inputStream; private OutputStream outputStream; private RandomAccessFile file; private FileChannel channel; private long offs = EMPTY_OFFS; private long size = 0; public DiskQueue(String filename) { try { boolean fileExists = new File(filename).exists(); file = new RandomAccessFile(filename, "rwd"); if (fileExists) { size = file.readLong(); offs = file.readLong(); } else { file.writeLong(size); file.writeLong(offs); } } catch (FileNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } channel = file.getChannel(); inputStream = Channels.newInputStream(channel); outputStream = Channels.newOutputStream(channel); } /** * Add item to end of queue. */ public void add(ItemT item) { try { synchronized (this) { channel.position(channel.size()); ObjectOutputStream s = new ObjectOutputStream(outputStream); s.writeObject(item); s.flush(); size++; file.seek(0); file.writeLong(size); if (offs == EMPTY_OFFS) { offs = HEADER_SIZE; file.writeLong(offs); } notify(); } } catch (IOException e) { throw new RuntimeException(e); } } /** * Clears overhead by moving the remaining items up and shortening the file. */ public synchronized void defrag() { if (offs > HEADER_SIZE && size > 0) { try { long totalBytes = channel.size() - offs; ByteBuffer buffer = ByteBuffer.allocateDirect((int) totalBytes); channel.position(offs); for (int bytes = 0; bytes < totalBytes;) { int res = channel.read(buffer); if (res == -1) { throw new IOException("Failed to read data into buffer"); } bytes += res; } channel.position(HEADER_SIZE); buffer.flip(); for (int bytes = 0; bytes < totalBytes;) { int res = channel.write(buffer); if (res == -1) { throw new IOException("Failed to write buffer to file"); } bytes += res; } offs = HEADER_SIZE; file.seek(LONG_SIZE); file.writeLong(offs); file.setLength(HEADER_SIZE + totalBytes); } catch (IOException e) { throw new RuntimeException(e); } } } /** * Returns the queue overhead in bytes. */ public synchronized long overhead() { return (offs == EMPTY_OFFS) ? 0 : offs - HEADER_SIZE; } /** * Returns the first item in the queue, blocks if queue is empty. */ public ItemT peek() throws InterruptedException { block(); synchronized (this) { if (offs != EMPTY_OFFS) { return readItem(); } } return peek(); } /** * Returns the number of remaining items in queue. */ public synchronized long size() { return size; } /** * Removes and returns the first item in the queue, blocks if queue is empty. */ public ItemT take() throws InterruptedException { block(); try { synchronized (this) { if (offs != EMPTY_OFFS) { ItemT result = readItem(); size--; offs = channel.position(); file.seek(0); if (offs == channel.size()) { truncate(); } file.writeLong(size); file.writeLong(offs); return result; } } return take(); } catch (IOException e) { throw new RuntimeException(e); } } /** * Throw away all items and reset the file. */ public synchronized void truncate() { try { offs = EMPTY_OFFS; file.setLength(HEADER_SIZE); size = 0; } catch (IOException e) { throw new RuntimeException(e); } } /** * Block until an item is available. */ protected void block() throws InterruptedException { while (offs == EMPTY_OFFS) { try { synchronized (this) { wait(); file.seek(LONG_SIZE); offs = file.readLong(); } } catch (IOException e) { throw new RuntimeException(e); } } } /** * Read and return item. */ @SuppressWarnings("unchecked") protected ItemT readItem() { try { channel.position(offs); return (ItemT) new ObjectInputStream(inputStream).readObject(); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } } }

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  • Google I/O 2012 - How to Build Apps that Love Each Other with Web Intents

    Google I/O 2012 - How to Build Apps that Love Each Other with Web Intents Paul Kinlan, James Hawkins Web Intents allows you to build applications that integrate with one another with an ease that has never been seen on the web before. In this session we will show you how to connect applications using Web Intents and how to best integrate with the many actions available in Web Intents such as editing, saving and sharing. For all I/O 2012 sessions, go to developers.google.com From: GoogleDevelopers Views: 1394 15 ratings Time: 57:48 More in Science & Technology

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  • Indefinite loops where the first time is different

    - by George T
    This isn't a serious problem or anything someone has asked me to do, just a seemingly simple thing that I came up with as a mental exercise but has stumped me and which I feel that I should know the answer to already. There may be a duplicate but I didn't manage to find one. Suppose that someone asked you to write a piece of code that asks the user to enter a number and, every time the number they entered is not zero, says "Error" and asks again. When they enter zero it stops. In other words, the code keeps asking for a number and repeats until zero is entered. In each iteration except the first one it also prints "Error". The simplest way I can think of to do that would be something like the folloing pseudocode: int number = 0; do { if(number != 0) { print("Error"); } print("Enter number"); number = getInput(); }while(number != 0); While that does what it's supposed to, I personally don't like that there's repeating code (you test number != 0 twice) -something that should generally be avoided. One way to avoid this would be something like this: int number = 0; while(true) { print("Enter number"); number = getInput(); if(number == 0) { break; } else { print("Error"); } } But what I don't like in this one is "while(true)", another thing to avoid. The only other way I can think of includes one more thing to avoid: labels and gotos: int number = 0; goto question; error: print("Error"); question: print("Enter number"); number = getInput(); if(number != 0) { goto error; } Another solution would be to have an extra variable to test whether you should say "Error" or not but this is wasted memory. Is there a way to do this without doing something that's generally thought of as a bad practice (repeating code, a theoretically endless loop or the use of goto)? I understand that something like this would never be complex enough that the first way would be a problem (you'd generally call a function to validate input) but I'm curious to know if there's a way I haven't thought of.

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  • How to manage a Closed Source High-Risk Project?

    - by abel
    I am currently planning to develop a J2EE website and wish to bring in 1 developer and 1 web designer to assist me. The project is a financial app with a niche market. I plan to keep the source closed . However, I fear that my would-be employees could easily copy the codebase and use it /sell it to a third party especially when they switch jobs. The app development will take 4-6months and perhaps more and I may have to bring in people after the app goes live. How do I keep the source to myself. Are there techniques companies use to guard their source. I foresee disabling pendrives and dvd writers on my development machines, but uploading data or attaching the code in one's mail would still be possible. My question is incomplete. But programmers who have been in my situation, please advice. How should I go about this? Building a team, maintaining code-secrecy,etc. I am looking forward to sign a secrecy contract with the employees if needed too. (Please add relevant tags) Update Thank you for all the answers. I certainly won't be disabling all USB ports and DVD writers now. But I think I should be logging activity(How exactly should I do that?) I am wary of scalpers who would join and then run off with the existing code. I haven't met any, but I have been advised to be wary of them. I would include a secrecy clause, but given this is a startup with almost no funding and in a highly competitive business niche with bigger players in the field, I doubt I would be able to detect or pursue any scalpers. How do I hire people I trust, when I don't know them personally. Their resume will be helpful but otherwise trust will develop only with time. But finally even if they do run away with the code, it is service that matters after the sale is made. So I am not really worried for the long term.

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  • JDK 7 In Action - Learn With Java Tutorials and Developer Guides

    - by sowmya
    At JavaOne 2012, Stuart Marks, Mike Duigou, and Joe Darcy gave a presentation about JDK 7 In Action. Learn more about using JDK 7 features with the help of Java Tutorials and JDK 7 Developer Guides. Links to relevant information are provided below. If you are considering moving to JDK 7 from a previous release, the JDK 7 Release Notes and JDK 7 Adoption Guide are great resources. Project Coin Features Improved Literals * Literals section in Primitive Datatypes topic. * Binary Literals * Underscores in Numeric Literals Strings In Switch * Strings In Switch Diamond * Type Inference for Generic Instance Creation * Type Inference and Instantiation of Generic Classes Multi-catch and Precise Throw * Catching Multiple Exception Types and Rethrowing Exceptions with Improved Type Checking * Catch Blocks Try-with-resources * The try-with-resources Statement NIO.2 File System API * File I/O for information on path, files, change notification, and more * Zip File System Provider * Zip File System Provider * Developing a Custom File System Provider Fork Join Framework * Fork/Join - Sowmya

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  • Geo for Good Summit Highlights

    Geo for Good Summit Highlights The last week of September, Google hosted the Geo for Good User Summit, for nonprofit mapping and technology specialists to update the nonprofit community about new and special features of Google's mapping products. In this week's Maps Developers Live event, Mano Marks from Maps Developer Relations and Raleigh Seamster, Program Manager with the Google Earth Outreach team will talk about the highlights of the Summit and show off some great examples of people using Maps to help the world. From: GoogleDevelopers Views: 0 0 ratings Time: 00:00 More in Education

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