Manipulating Java Class Files with BCEL - Part Three: More About BCEL

This is the third article in the BCEL series. You can read all here. Since I have covered the basics, I will accumulate the points left now. I will discuss about local variables, fields, methods and jump instructions.

Manipulating Java Class Files with BCEL - Part Two: Expressions

This is the second article in the series of articles on Apache BCEL. If you have not read part 1, read it here.

Expression Processing: Expressions are key part of a language. In this article, I will discuss how expressions are compiled into java byte code. I will also cover a little bit about compilation process. At the end, I will go through the steps and create a compiler for numerical expression.

Manipulating Java Class Files with BCEL - Part One : Hello World!

What is BCEL: Apache BCEL or Byte Code Engineering Library is a library that enables simpler manipulation of java byte code. Now the question is, why manipulate byte code? There can be a million of reasons. For example, you might want to insert some profiling code in the class file. Or you might want to write your own language that compiles to java byte code. You can also provide some attractive extension to some framework you are creating. Or you can even be more creative than I am and do something that I cannot think of. But for that, you must first understand how java class files work.

Since it is a BCEL tutorial, get the BCEL library first from here

Manipulating java byte code directly is not trivial in nature, so I decided to break the tutorial into a series. This one is the first - the hello world. Keep in touch to learn more.

Java Threads - How They Work

What is Thread: A thread is a single sequence of instructions being executed in a java virtual machine. The instructions in two different threads have no mutual ordering, they can execute independent of each other.

How to create a thread: In java, the only way to create a thread is by creating an object of class java.lang.Thread. In reality, we can either extend the Thread class and override the method run(), or we can implement java.lang.Runnable in a separate class and pass it to Thread's constructor. This article is meant for people who have some experience with Thread programming in java. If you do not know how to do thread programming in java, there is a very good tutorial in here.

An Anatomy of Java Generics

1. What is Generics: Generics is a feature in java language to create parameterized types. A parameterized type is a type with parameters passed to it, mostly to enable compiler to check for errors which otherwise would have been a runtime exception.

For example, let us consider programs below. In the first one, generics is not used. We are using java collection API to store and retrieve objects. In this program, it is impossible for the compiler to know what actually is stored in the collection. It is the programmer's job to take care that the objects stored are of expected type and that they are not cast to a wrong type in the time of retrieval. Not only this takes a lot of nasty boiler plate code, it also obfuscates the purpose of the collection all together. Generics attempts to solve this by passing parameters to type to specify what the types are related to. As we will see.

Floating Point Numbers

What is a Floating Point Number: There are two ways a decimal/fractional number can be represented in binary form - fixed point and floating point. In a fixed point number, the decimal point is in a fixed arbitrary position which is predefined. For example, in a 32 bit fixed point number, the decimal point may be assumed to be after the 16th bit. So any value represented by the 32 bits needs to be divided by 216 = 65536, to get the value of the decimal number represented by a fixed point.

A floating point number on the other hand has a completely different representation. A floating point number compromises on precision for achieving the following.

1. Broader range of numbers that it can represent
2. The precision of the number is fixed, irrespective of its value
3. Represent special values like infinity and not-a-number

Bit Patterns of a Floating Point Number: As per IEEE 754, the floating point numbers are of two types - 32 bit single precision and 64 bit double precision.

Java enterprise framework developers' tools

Wanna develop your own framework? Developing your own framework is sure geeky. Fortunately, in Java, doing so is not as difficult as it seems. But, why develop a framework when there are too many of them already available there? Well, firstly its fun, but more importantly, the existing frameworks might not right away give you all you need. In that case, it might be a good idea to at least extend those frameworks to meet your needs.

Please note that there are so many things you can use and my list is definitely not exhaustive. It just gives idea about a few good ones that come bundled with Java SE.