Static import in Java allows to import static members of class and use them, as they are declared in the same class. Static import is introduced in Java 5 along with other features like Generics, Enum, Autoboxing and Unboxing and variable argument methods. Many programmer think that using static import can reduce code size and allow you to freely use static field of external class without prefixing class name on that. For example without static import you will access static constant MAX_VALUE of Integer class as Integer.MAX_VALUE but by using static import you can import Integer.MAX_VALUE and refer it as MAX_VALUE. Similar to regular import statements, static import also allows wildcard * to import all static members of a class. In next section we will see Java program to demonstrate How to use static import statements to import static fields.
Monday, October 29, 2012
Saturday, October 27, 2012
What is difference between java.sql.Time, java.sql.Timestamp and java.sql.Date - JDBC interview Question
Difference between java.sql.Time, java.sql.Timestamp and java.sql.Date is most common JDBC question appearing on many core Java interviews. As JDBC provides three classes java.sql.Date, java.sql.Time and java.sql.Timestamp to represent date and time and you already have java.util.Date which can represent both date and time, this question poses lot of confusion among Java programmer and that’s why this is one of those tricky Java questions which is tough to answer. It becomes really tough if differences between them is not understood correctly. We have already seen some frequently asked or common JDBC questions like why JDBC has java.sql.Date despite java.util.Date and Why use PreparedStatement in Java in our last tutorials and we will see difference between java.sql.Date, java.sql.Time and java.sql.Timestamp in this article. By the way apart from these JDBC interview questions, if you are looking to get most from JDBC you can also see 4 JDBC performance tips and 10 JDBC best practices to follow. Those article not only help you to understand and use JDBC better but also help on interviews. Let’s come back to difference sql time, timestamp and sql date.
Friday, October 26, 2012
JSTL foreach loop in JSP
JSTL foreach tag is pretty useful while writing Java free JSP code. JSTL foreach tag allows you to iterate or loop Array List, HashSet or any other collection without using Java code. After introduction of JSTL and expression language(EL) it is possible to write dynamic JSP code without using scriptlet which clutters jsp pages. JSTL foreach tag is a replacement of for loop and behaves similarly like foreach loop of Java 5 but still has some elements and attribute which makes it hard for first-timers to grasp it. JSTL foreach loop can iterate over arrays, collections like List, Set and print values just like for loop. In this JSP tutorial we will see couple of example of foreach loop which makes it easy for new guys to understand and use foreach loop in JSP. By the way this is our second JSP tutorial on JSTL core library, in last tutorial we have seen How to use core <c:set> tag in JSP page.
Thursday, October 25, 2012
Eclipse IDE provides quick shortcut keys to print System.out.println statement in Java but unfortunately not every Java programmers are familiar of that. Even programmers with 3 to 4 year of experience sometime doesn't know this useful Eclipse shortcut to generate System.out.println messages. This Eclipse tips is to help those guys. Let me ask you one question, How many times you type System.out.println in your Java program? I guess multiple time, while doing programming, debugging and testing small stuff. System.out.println is most preferred way to print something on console because it doesn’t required setup like configuring Log4J or java.util.Logger . Though I recommend using logging for better information display in production code, nobody can undermine importance of System.out.println statement in Java. On the quest of learning Eclipse shortcut, some of them which I have discussed in my list of Top 30 Eclipse shortcut for Java programmers, I found a very useful Eclipse shortcut for generating code for System.out.println statement in Java source file. By using this Eclipse shortcut you can create System.out.println() messages in 60% less time, as you only need to type the message. This Eclipse shortcut will place your cursor right in the place, where it should be i.e. inside System.out.println method.
Calculate area of Triangle in JavaWrite a Java program to calculate Area of Triangle, accept input from User and display output in Console is one of the frequently asked homework question. This is not a tough programming exercise but a good exercise for beginners and anyone who has started working in Java. For calculating area of triangle using formula 1/2(base*height), you need to use arithmetic operator. By doing this kind of exercise you will understand how arithmetic operators works in Java, subtle details which affect calculation like precedence and associativity of operator etc. Fortunately this question is not very popular on Java interview like other exercise we have seen e.g. Java program to print Fibonacci series and Java program to check for palindrome. Nevertheless its a good Java homework.
Tuesday, October 23, 2012
notify vs notifyAll in Java
What is difference between notify and notifyAll method is one of the tricky Java question, which is easy to answer but once Interviewer ask followup questions, you either got confused or not able to provide clear cut and to the point answers. Main difference between notify and notifyAll is that notify method will only notify one Thread and notifyAll method will notify all Threads which are waiting on that monitor or lock. By the way this is something you have been reading in all over places and to be frank, this statement despite being correct is not complete and its very difficult to understand difference between notify vs notifyAll by just reading this statement. Lot of questions comes in mind like
Which thread will be notified if I use notify()?
How do I know how many threads are waiting, so that I can use notifyAll() ?
How to call notify()?
What are these thread waiting for being notified etc.
Actually discussion of notify and notifyAll is incomplete without discussing wait method in Java and I had touched based on this on my earlier article why wait and notify must be called from synchronized context. In order to get answer of those questions and understand difference between notify and notifyAll we will use a simple Java Thread example using wait and notify code :
Saturday, October 20, 2012
How to add JAR file to Classpath in Java
Adding JAR into classpath is a common task for Java programmer and different programmer do it on different way. Since Java allows multiple ways to include JAR file in classpath, it becomes important to know pros and cons of each approach and How exactly they work. There are 5 ways to add jars on into classpath in Java some of them we have already seen in How classpath works in Java and How to set Path in Java. In this post we will revisit some of those techniques and explore Java 1.6 wildcard to add multiple JAR into classpath. By the way here is 5 ways to add JAR file into classpath. In short knowledge of Path, Classpath and Classloaders are must for any Java programmer, not only from knowledge point of view but also to successfully debug and resolve issues related to Classpath e.g. NoClassDefFoundError and java.lang.ClassNotFoundException in Java.
Friday, October 19, 2012
Regular Expression to check numeric String
In order to build a regular expression to check if String is number or not or if String contains any non digit character or not you need to learn about character set in Java regular expression, Which we are going to see in this Java regular expression example. No doubt Regular Expression is great tool in developer arsenal and familiarity or some expertise with regular expression can help you a lot. Java supports regular expression using java.util.regex.Pattern and java.util.regex.Matchter class, you can see a dedicated package java.util.regex for regular expression in Java. Java supports regex from JDK 1.4, means well before Generics, Enum or Autoboxing. If you are writing server side code in Java programming language than you may be familiar with importance of regular expression which is key in parsing certain kind of messages e.g. FIX Messages used in Electronic trading. In order to parse Repeating groups in FIX protocol you really needs understanding of regular expression in Java. Any way In order to learn validating numbers using regular expression we will start with simple example
private vs public vs protected vs package in Java
Java has four access modifier namely private, protected and public. package level access is default access level provided by Java if no access modifier is specified. These access modifier is used to restrict accessibility of a class, method or variable on which it applies. We will start from private access modifier which is most restrictive access modifier and then go towards public which is least restrictive access modifier, along the way we will see some best practices while using access modifier in Java and some examples of using private and protected keywords.
Tuesday, October 16, 2012
GC Interview Questions Answer in Java
Garbage collection interview questions are very popular in both core Java and advanced Java Interviews. Apart from Java Collection and Thread many tricky Java questions stems Garbage collections which are tough to answer. In this Java Interview article I will share some questions from GC which is asked in various core Java interviews.These questions are based upon concept of How Garbage collection works, Different kinds of Garbage collector and JVM parameters used for garbage collection monitoring and tuning. As I said GC is an important part of any Java interview so make sure you have good command in GC. One more thing which is getting very important is ability to comprehend and understand Garbage collection Output, more and more interviewer are checking whether candidate can understand GC output or not. During Java interview they may provide a snippet of GC output and ask various questions based on that e.g. Which Garbage collector is used, whether output is from major collection or minor collection, How much memory is free from GC, What is size of new generation and old generation after GC etc. I have included few Garbage collection interview questions and answers from GC output to help with that. It’s recommended to prepare questions from Java collection, multithreading and programming along with Garbage collection to do well in Java interviews at any stage.
Saturday, October 13, 2012
How to get input from user in Java from command line or console is one of the common thing ,every one started learning Java looks for. It’s second most popular way of starting programming after HelloWorld in Java. There are so many ways to get input from User in Java including command line and Graphical user interface. For beginner simpler the example, better it is. first and foremost way of getting input from user is String passed to main method in Java but that only work for one time requirement and its not interactive. Another way of getting input from User is involving IO classes like InputStream to read from console or command line which can be little complicated for true beginner. Thanks to Java 5 which added a nice utility class called Scanner, has made task of getting input from user very easy. Scanner is powerful and allows you to get any kind of input from User e.g. String, int, float etc.
Friday, October 12, 2012
How to remove all unused imports in Eclipse
Eclipse IDE gives warning "The import XXX is never used" whenever it detect unused import in Java source file and shows a yellow underline. Though unused import in Java file does not create any harm, its unnecessary increase length and size of Java source file and if you have too many unused imports in your Java source file, those yellow underline and Eclipse warning affect readability and working. In our last post on Eclipse, we have seen dome Java debugging tips on Eclipse and in this post we will see Eclipse shortcut to remove all unused imports in Eclipse. There are many option to tackle with this problem e.g. you can collapse import section of code in Eclipse or you can altogether remove all unused imports from Java file. Since Eclipse is favorite IDE of many Java programmer, who love to do things fast in shortcuts, I will also shared Eclipse shortcut to remove unused imports from Java program in this article. This is one of many Eclipse shortcuts which we have discussed in our post Top 30 Eclipse keyboard shortcut for Java programmer. Let's see How to remove all unused imports from Java file in Eclipse IDE.
Sunday, October 7, 2012
10 Java String interview Question answers
String interview questions in Java is one of Integral part of any Core Java or J2EE interviews. No one can deny importance of String and How much it in any Java application irrespective of whether its core Java desktop application, web application, Enterprise application or Mobile application. String is one of the fundamental of Java programming language and correct understanding of String class is must for any Java programmer. What makes String interview questions in Java even more interesting is the special status of String in terms of features and privileges it has, like + operator is kind of overloaded to perform String concatenation despite the fact that Java does not support operator overloading. There is a separate String pool to store String literal etc. In this article we will some frequently asked question on String in a Java interview which focuses on range of issues like immutability, thread-safety, Security etc.
Saturday, October 6, 2012
Inheritance in Java is an Object oriented or OOPS concepts, which allows to emulate real world Inheritance behavior, Inheritance allows code reuse in Object oriented programming language e.g. Java. Along with Abstraction, Polymorphism and Encapsulation, Inheritance forms basis of Object oriented programming. Inheritance is implemented using extends keyword in Java and When one Class extends another Class it inherit all non private members including fields and methods. Inheritance in Java can be best understand in terms of Parent and Child class, also known as Super class and Sub class in Java programming language. The class which extends another class becomes Child of the class it extends and inherit all its functionality which is not private or package-private given where Child class is created. Inheritance is the most easy way to reuse already written and tested code but not always best way to do so, which we will see in this article. There are lot of example of Inheritance in Object oriented world e.g. Child inherit properties from parent, Dog inherit properties of Animal etc. In this Java and OOPS tutorial we will learn What is Inheritance in Java, How to use Inheritance in Java, Simple Example of Java Inheritance and some important points about Inheritance in Java.