Why Catching Throwable or Error is bad?

We often hear advice that catching Throwable or Error is bad practice and Java developer should avoid catching these, but have you thought Why? If language allows you to catch anything which is instance of java.lang.Throwable, then what is the problem of catching them or their subclass java.lang.Error? If they are bad, shouldn't Java itself has prohibited them from catching? Well this all looks good on theory, but not in real world programming. As I said before in Java Exception best practices post, Ideally you should never catch Throwable or in particular Error. There are several reasons why catching instance of java.lang.Throwable is bad idea, because in order to catch them you have to declare at your method signature e.g. public void doSomething() throws Throwable. When you do this, no body knows what kind of Error this method is going to throw, and until you know what is the problem, how can you resolve that. Main purpose of providing Exception handling mechanism is to handle error situation properly, but you can't a provide a solution which can solve all problems. That's why we have specific Exception classes e.g. FileNotFoundException, IllegalArgumentException, IOException and so on. So if you don't know how to resolve or handle error, there is no point catching Throwable, all it make your code hard to read and comprehend. Remember, each error handling code is driven by business/audit/reporting or quality requirement and catching Throwable just obscure those logics.

Read more �

Top 30 Java Phone Interview Questions Answers for Freshers, 1 to 2 Years Experienced

In this article, I am sharing 30 core Java technical questions, from screening and phone round of interviews. In telephonic interviews, questions are short, fact based and Interviewer expects some keyword in answers. Accordingly, I have given very short answers to these question, only main points; just to make this as revision post. I am expecting every Java programmer to know answers of all these Java technical questions, if he has more than 4 to 5 years experience. it's only freshers, and junior developers who needs to do bit of research to understand topics well. I have tried to include all classical and hugely popular, frequently asked questions from different topics like String, multi-threading, collection, design pattern, object oriented design, garbage collection, generics and advanced Java concurrency questions. Since core Java interviewer's normally don't ask questions on JSP, Servlets and other JEE technologies, I have not included them into this list. Sole purpose of this list is to given freshers and less experienced developers an idea of what kind of core Java technical questions are asked on phone interviews. For curious ones, I have also included links for more detail answers and discussions.

Read more �

Difference between static vs non static method in Java

In this article, we will take a look at difference between static and non static method in Java, one of the frequently asked doubt from Java beginner. In fact, understanding static keyword itself is one of the main programming fundamental, thankfully it's well defined in Java programming language . A static method in Java belongs to class, which means you can call that method by using class name e.g. Arrays.equals(), you don't need to create any object to access these method, which is what you need to do to access non static method of a class. Static method are treated differently by compiler and JVM than non static methods, static methods are bonded during compile time, as opposed to binding of non static method, which happens at runtime. Similarly you can not access non static members inside static context, which means you can not use non static variables inside static methods, you can not call non static methods from static ones, all those will result in compile time error. Apart from these significant differences between static and non static methods, we will also take a look at few more points in this Java tutorial, with a code example, which shows some of these differences in action.By the way this is the second article on static method, in first article, we have learned about when to use static method in Java

Read more �

How clone method works in Java

clone is a tricky method from java.lang.Object class, which is used to create copy of an Object in Java. Intention of clone() method is simple, to provide a cloning mechanism, but some how it's implementation became tricky and has been widely criticized from long time. Anyway, we will not go to classic debate of clone in Java, at-least for now; instead, we will try to learn how clone method works in Java. To be fair, understating cloning mechanism in Java is not easy and even experienced Java programmer fail to explain how cloning of mutable object works, or difference between deep copy and shallow copy in Java. In this three part article, we will first see working of clone method in Java, and in second part we will learn how to override clone method in Java, and finally we will discuss deep copy vs shallow copy mechanism. The reason I chose to make this a three part article, is to keep focus on one thing at a time. Since clone() itself is confusing enough, it's best to understand concept one by one. In this post, we will learn what is clone method, what it does and How clone method works in Java. By the way, clone() is one of the few fundamental methods defined by objects, others being equals, hashcode(), toString() along with wait and notify methods.

Read more �

10 Equals and HashCode Interview Questions in Java

Equals and HashCode methods in Java are two fundamental methods from java.lang.Object class, which is used to compare equality of objects, primarily inside hash based collections such as Hashtable and HashMap. Both equals() and hashCode() are defined in java.lang.Object class and there default implementation is based upon Object information e.g. default equals() method return true, if two objects are exactly same i.e. they are pointing to same memory address, while default implementation of hashcode method return int and implemented as native method. Similar default implementation of toString() method, returns type of class, followed by memory address in hex String. It's advised to override these method, based upon logical and business rules e.g. String overrides equals to check equality of two String based upon content, we have also seen and example implementation of equals() and hashCode for custom classes. Because of there usefulness and usage, they are also very popular in various level of Java Interviews, and In this tutorial, I am going to shared some of the really interesting questions from equals() and hashCode() method in Java. This question not only test your concept on both method, but also gives an opportunity to explore them more.

Read more �

Swing is not thread-safe in Java - What does it mean? Event Dispatcher, SwingWorker, Multithreading and Best Practices

Couple of my reader ask question, what does it mean by Swing is not thread-safe and How does it affect coding in Swing GUI application? This post is an effort to help those readers and several other programmers to understand Swing and thread-safety in a bit more detailed way. To keep it simple, let's revise what does it mean by being thread-safe? We say an object is thread-safe, if we can call it's method, which can change it's state, from multiple thread at same time. To give you an example, java.lang.String is a thread-safe class, which means you can call any method e.g. substring(), toUpperCase() or toLowerCase() from multiple threads. By the way, String is thread-safe because it's immutable. Let's come back to Swing now, Core part of Swing is made up of different GUI component e.g. JLable, JPanel, JCombobox etc. All these components are not thread-safe, which means you can not call methods of this components e.g. JLable.setText("new title") from any thread, other than Event Dispatcher Thread(EDT). In one word, Since Swing is not thread-safe, you can not update Swing components from any random thread, they are always updated using Event Dispatcher thread. This is in fact one of the most popular Java Swing Interview Question, with lot's of interesting follow-up e.g. If Swing is not thread-safe than how do you update components from other thread? and which methods of Swing API are thread-safe? etc. We will see answer of this question in next section.

Read more �