Knowledge Cafe

J ava thread safety problems can bring down your Java EE application and the Java EE container fairly easily. One of most common problems I have observed when troubleshooting Java EE performance problems is infinite looping triggered from the non-thread safe HashMap get() and put() operations. There seem to be three different synchronized Map implementations in the Java API: Hashtable Collections.synchronizedMap(Map) ConcurrentHashMap ConcurrentHashMap in Java is introduced as an alternative of Hashtable in Java 1.5 as part of Java concurrency package. Prior to Java 1.5 if you need a Map implementation, which can be safely used in a concurrent and multi-threaded Java program, than, you only have Hashtable or synchronized Map because HashMap is not thread-safe. With ConcurrentHashMap, now you have better choice; because, not only it can be safely used in concurrent multi-threaded environment but also provides better performance...

Atomic is a toolkit of variable java.util.concurrent.atomic package classes, which assist in writing lock and wait-free algorithms with the Java language. When a data (typically a variable) can be accessed by several threads, you must synchronize the access to the data to ensure visibility and correctness. By example, if you have a simple counter: public class Counter { private int value; public int getValue(){ return value; } public int getNextValue(){ return value++; } public int getPreviousValue(){ return value--; } } This class works really well in single-threaded environment, but don’t work at all when several threads access the same Counter instance. You can solve the problem using synchronized method as below public class SynchronizedCounter { private int value; public synchronized int getValue(){ return value; } public synchronized int getNextValue(){ return value++; } public synchronize...

Writing or creating immutable classes in Java is becoming popular day by day, because of concurrency and multithreading advantage provided by immutable objects. Immutable objects offers several benefits over conventional mutable object, especially while creating concurrent Java application. Immutable object not only guarantees safe publication of object’s state, but also can be shared among other threads without any external synchronization. In fact JDK itself contains several immutable classes like String, Integer and other wrapper classes. For those, who doesn’t know what is immutable class or object, Immutable objects are those, whose state can not be changed once created e.g. java.lang.String, once created can not be modified e.g. trim, uppercase, lowercase. All modification in String result in new object, see why String is immutable in Java for more details. In this Java programming tutorial, we will learn, how to write immutable class in Java or how to make a class immutable. By ...

Multi-threading and concurrency questions are essential part of any Java interview. If you are going for any Java interview on any Investment bank for equities front office position expect lots of muti-threading interview questions on your way. Multi-threading and concurrency is a favorite topics on Investment banking specially on electronic trading development and they grill candidate on many confusing java thread interview questions. They just want to ensure that the guy has solid knowledge of multi-threading and concurrent programming in Java because most of them are in business of performance. High volume and low latency Electronic trading System which is used for Direct to Market (DMA) trading is usually concurrent in nature. These are my favorite thread interview questions on Java asked on different on different time. I am not providing answer of these thread interview questions but I will give you hint whenever possible, some time hint is enough to answer. I will update the post...