Wednesday, July 30, 2014

How to Load Resources from Classpath in Java with Example

Classpath in Java is not only used to load .class files, but also can be used to load resources e.g. properties file, images, icons, thumbnails, or any binary content. Java provides API to read these resources as InputStream or URL. Suppose, you have a properties file inside config folder of your project, and you want to load that properties file, how do you do that? Similarly, you have icons and thumbnails for your web applications on icons directory of your project, how do you load them? Answer is by using java.lang.Class' getResource() and getResourceAsStream() method. These method accepts path of resource as String and returns URL and InputStream respectively. You can obtain a reference of Class by calling either getClass() method or by using class literal. If you have an object, then you can call getClass() because its a non-static method, on the other hand, if you don't have any object, you can simply use .class with name of any class e.g. Sample.class will give you reference of java.lang.Class. These methods are available from JDK 1.1 and you can even use them anywhere you have access to core Java library. If you are creating J2ME games or application, you can use these method to load icons and tiles for your game, and all other resource for your application as well.

Monday, July 28, 2014

Default, Defender or Extension Method of Java 8 with Example

Java 8 now allows you to add non-abstract method implementations to interfaces by utilizing the default and static keyword. Methods with default keyword are known as default methods or defender methods in Java. Before Java 8, it was virtually impossible to change an interface once published. Any change e.g. addition of a new method would have broken all clients. That's why when Java 8 decided to switch to internal iterator implementation using forEach() method, they face a daunting challenge of breaking all implementation of Iterable interface. Since backward compatibility is top priority for Java engineers, and it wasn't practical to break all clients, they came up with idea of default method. This is an amazing and very powerful change, because now you can evolve your existing interface with all the knowledge you have gained after using them. JDK itself is utilizing default methods in big way, java.util.Map interface is extended with several new default methods e.g. replaceAll(), putIfAbsent(Key k, Value v) and others. By the way, Since default method allows extension of existing interface, it’s also known as Extension method. You are also free to define any number of default method in your interface. I think after this change, you unlikely need an abstract class to provide skeletal implementation as described in Effective Java e.g. List comes with AbstractList, Collection comes with AbstractCollection, Set comes with AbstractSet and Map comes with AbstractMap. Instead of creating a new abstract class with default implementation, you can define them as default method inside interface itself. Similarly, introduction of static methods inside interface will make pattern of an interface utility class redundant e.g. Collections for Collection interface, Paths for Path and so on. You can directly define static utility method on interface itself.

Wednesday, July 23, 2014

Java ArrayList and HashMap Performance Improvement in JDK 1.7| Empty List and Map will Cost Less Memory

From long time one reason for me to update to newer Java version was always bug fix and performance improvement. Apart from major changes like Generics in Java 1.5 and Lambdas in Java 8, there are so many small improvements, performance optimization which just goes under radar, one of such change is creating empty ArrayList and HashMap with size zero in JDK 1.7.0_40 update. Many Java developer doesn't even know about these changes, part of the blame lies on Java developers like me, as I hardly read release notes of minor Java updates. Some times these changes are done as part of bug fixes and other time as minor optimization, but given popularity of ArrayList and HashMap in Java application impact of this simple Java optimization is huge. If you are running on Java 1.6 or earlier version of Java 1.7, you can open code of java.util.ArrayList and check that, currently empty ArrayList is initialized with Object array of size 10. If you create several temporary list in your program, which remains uninitialized, due to any reason then you are not only losing memory but also losing performance by giving your garbage collector more work. Same is true for empty HashMap, which was initialized by default initial capacity of 16. This changes are result of observation made by Nathan Reynolds, and Architect at Oracle, which apparently analysed 670 Java heap dumps from different Java programs to find out memory hogs.