Wednesday, 30 November 2016

How to convert Timestamp to Date in Java - JDBC

The JDBC API uses separate Date, Time and Timestamp class to confirm DATE, TIME and DATETIME data type from the database, but most of the Java object oriented code is written in java.util.Date. This means you need to know how to convert the timestamp to date and vice-versa. You can do by using the getTime() method, which return the number of millisecond from Epoch value. This can be used to create both Timestamp and java.util.Date, hence it acts as a bridge between Date class from java.util package and Date, Time and Timestamp class from the java.sql package.

Tuesday, 29 November 2016

Auto-Generate Optimized Java Class Specializations

Background

As you might know, Java has a number of built-in value types. These are bytes, shorts, integers, longs, floats, doubles, booleans and characters. Primitive value types are different from ordinary objects primarily in that they can be allocated directly on the memory stack, reducing the burden on the Garbage Collector. A problem with not inheriting from Object is that they can’t be put into collections or passed as parameters to methods that take object parameters without being wrapped. Typical wrapper classes are therefore “Integer”, “Double”, “Boolean” etc.

Monday, 28 November 2016

Inheriting Javadoc Method Comments

The following interfaces and classes are contrived examples that will be used in this post to illustrate inheritance of Javadoc comments on methods. Some inherited/implementing methods include their own Javadoc comments that override parent’s/interface’s methods comments fully or partially and other simply reuse the parent’s/interface’s methods’ documentation.

Saturday, 26 November 2016

What is Polymorphism in Java? Overriding or Overloading?

Polymorphism vs Overloading vs Overriding

Someone asked me What are the difference between Polymorphism and Overriding in Java and the similar difference between Polymorphism and Overloading. Well, they are not two different things, Polymorphism is an object oriented or OOPS concept like Abstraction, Encapsulation or Inheritance which facilitate the use of the interface and allows Java program to take advantage of dynamic binding in Java. Polymorphism is also a way through which a Type can behave differently than expected based upon which kind of Object it is pointing. Overloading and overriding are two forms of Polymorphism available in Java.

Friday, 25 November 2016

Default Methods in Java 8 and Multiple Inheritance

Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit characteristics and features from more than one parent object or parent class.
Default methods in Java 8 can be viewed as a form of multiple inheritance (except that attribute can not be inherited). Consider the example below, the Button class implements two interfaces - Clickable and Accessible.

Wednesday, 23 November 2016

Difference between include() and forward() methods of RequestDispatcher in Servlert

What is the difference between include and forward methods of RequestDispatcher interface is one of the frequently asked Servlet questions from Java EE interviews and we'll see how you can answer this question on your interview. You get the RequestDispatcher reference either from ServletContext or ServletRequest interface and even though both include() and forward() method allow a Servlet to interact with another servlet, main difference between include() and forward is that include() method is used to load the contents of the specified resource (could be a Servlet, JSP, or static resource e.g. HTML files) directly into the Servlet's response, as if it is part of the calling Servlet. On the other hand, forward() method is used for server side redirection, where an HTTP request for one servlet is routed to another resource (Servlet, JSP file or HTML file) for processing.

Monday, 21 November 2016

Auto-Generate Optimized Java Class Specializations

If you visited JavaOne this year you might have attended my presentation on “How to Generate Customized Java 8 Code from your Database”. In that talk I showcased how the Speedment Open Source toolkit is used to generate all kinds of Java code using a database as the domain model. One thing we didn’t have time to go into though is the fact that Speedment is not only making code generation easier, it is also itself made up by generated code. In this article I will show you have we set up Speedment to generate specialized versions of many classes to reduce the memory footprint of performance critical parts of the system.

Monday, 14 November 2016

Java Annotations Are a Big Mistake

Annotations were introduced in Java 5, and we all got excited. Such a great instrument to make code shorter! No more Hibernate/Spring XML configuration files! Just annotations, right there in the code where we need them. No more marker interfaces, just a runtime-retained reflection-discoverable annotation! I was excited too. Moreover, I’ve made a few open source libraries which use annotations heavily. Take jcabi-aspects, for example. However, I’m not excited any more. Moreover, I believe that annotations are a big mistake in Java design.

Friday, 11 November 2016

Are You Still Debugging?

Debugging is “a process of running a program/method interactively, breaking execution flow after each statement and showing…” In a nutshell, it is a very useful technique … for a bad programmer. Or an old programmer who is still writing procedural code in C. Object-oriented programmers never debug their code—they write unit tests. My point here is that unit testing is a technique that completely replaces debugging. If debugging is required, the design is bad.

Thursday, 10 November 2016

How to solve java.sql.BatchUpdateException: String or binary data would be truncated

Recently I was working in Java application which uses Microsoft SQL Server at its backend. The architecture of Java application was old i.e. even though there was heavy database communication back and forth there was no ORM used e.g. no Hibernate, JPA, or Apache iBatis. The Java application was using old DAO design pattern, where the DB related classes which are responsible for loading and storing data from database was calling stored procedure to do their Job. These stored procedure takes data from Java application and insert into SQL Server tables. One day, one of my collegue called me to troubleshoot "java.sql.BatchUpdateException: String or binary data would be truncated", which it's application was throwing and he has no clue whatsoever that what is wrong with the data he is getting from other system and trying to store.

Resolve method calls in Java code using the JavaSymbolSolver

Why I created the java-symbol-solver?

A few years ago I started using JavaParser and then I started contributing. After a while I realized that many operations we want to do on Java code cannot be done just by using the Abstract Syntax Tree produced by a parser, we need also to resolve types, symbols and method calls. For this reason I have created the JavaSymbolSolver.

One thing that is missing is documentation: people open issues on JavaParser asking how to answer a certain question and the answer is often “for this you need to use JavaSymbolSolver”. Starting from these issues I will show a few examples.

Wednesday, 9 November 2016

5 Things Only Experienced Developers Can Teach You About Java

An overview of everything you need to know before diving deep into developing Java

There are numerous tools, methods, environments and features that change the way you handle your code, that you usually don’t come across during school years. While it offers the first foot through the door in the Java development world, most of the actual learning happens on the job.

In the following post we’ll go over some key elements you only learn about as you get more experienced. These will include the basics and mix in a some philosophy. Get your notebook ready, it’s back to school time.

Tuesday, 8 November 2016

Difference between PUT and POST in REST WebService in Java

If you remember REST WebServices uses HTTP methods to map CRUD (create, retrieve, update, delete) operations to HTTP requests. Even though both PUT and POST methods can be used to perform create and update operation in REST WebServices, Idempotency is the main difference between PUT and POST. Similar to the GET request, PUT request is also idempotent in HTTP, which means it will produce the same results if executed once more multiple times. Another practical difference PUT and POST method in the context of REST WebService are that POST is often used to create a new entity, and PUT is often used to update an existing entity. If you replace an existing entity using PUT than you should be aware that if only a subset of data elements is passed then the rest will be replaced by empty or null.

Monday, 7 November 2016

Explore Polymorphism in Java

Polymorphism is the existence of the same thing in various forms. It is a feature of OOP that enables items to change form based on circumstances. The term polymorphism is derived from two Greek words, namely, "poly" and "morphos." While the term "poly" means many, and "morphos" which implies forms. Hence, polymorphism denotes the existence of the same thing in various forms. The Java Programming Language has been one of the most popular programming languages for decades. It is widely used in enterprise software development and has matured a lot over the last decade. The Java Programming Language provides excellent support for polymorphism.

Saturday, 5 November 2016

How to Add and Subtract Two Matrices in Java

This is the second program in the series of matrices related programming exercises in Java. In the last program, you have learned matrix multiplication and in this program, you will learn how to perform addition and subtraction of two matrices in Java. We'll create methods to calculate both sum and difference of two matrices in Java program. In Mathematics, a matrix is a rectangular array with two dimensions known as rows and columns. In Java, your can use a two-dimensional array to represent a matrix because it also has two dimensions rows and columns. Since a 2D array is nothing but an array of the array in Java, the length of the outer array is equal to the number of rows and length of sub-array is equal to the number of columns.

Friday, 4 November 2016

How to compare String by their length in Java 7 and 8?

The natural way to compare String is the lexicographic way, which is implemented in the compareTo() method of String class, but sometimes you need to compare String by their length. You cannot use the default compareTo() method for that task, you need to write your own custom Comparator, which can compare String by length. Don't worry, It's easy to compare multiple String by their length, all you need to write is a Comparator which calculates their length using the length() method and compare them. Such comparator should return a positive value if first String has a length greater than second String, a negative value if the length of first String is less than the length of second String and zero if both String has the same length.