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.

Thursday, July 17, 2014

9 Difference between TCP and UDP Protocol - Java Network Interview Question

TCP and UDP are two transport layer protocols, which are extensively used in internet for transmitting data between one host to another. Good knowledge of how TCP and UDP works is essential for any programmer. That's why difference between TCP and UDP is one of the most popular programming interview question. I have seen this question many times on various Java interviews , especially for server side Java developer positions. Since FIX (Financial Information Exchange) protocol is also a TCP based protocol, several investment banks, hedge funds, and exchange solution provider looks for Java developer with good knowledge of TCP and UDP. Writing fix engines and server side components for high speed electronic trading platforms needs capable developers with solid understanding of fundamentals including data structure, algorithms and networking. By the way, use of TCP and UDP is not limited to one area, its at the heart of internet. The protocol which is core of internet, HTTP is based on TCP. One more reason, why Java developer should understand these two protocol in detail is that Java is extensively used to write multi-threaded, concurrent and scalable servers. Java also provides rich Socket programming API for both TCP and UDP based communication. In this article, we will learn key differences between TCP and UDP protocol, which is useful to every Java programmers. To start with, TCP stands for Transmission Control Protocol and UDP stands for User Datagram Protocol, and both are used extensively to build Internet applications.