Extreme Java

How does a garbage collector works

admins — Fri, 18 May 2012 14:56:15 +0000

Though the actual working of garbage collector is internal to JVM but there are some algorithms which can be used by any garbage collector. The two famous algorithms are described here: a) Mark and Sweep: This algorithm works by suspending all the currently executing user threads and starting to examine all the objects for a [...]

Is Java a pure object oriented language?

admins — Fri, 18 May 2012 14:54:53 +0000

For a language to pure object oriented, following features must be supported by the language: 1) Encapsulation/Data Hiding 2) Inheritance 3) Polymorphism 4) All pre-defined types are objects 5) All user-defined types are objects 6) All operations are defined as method calls on objects Java is not a pure object oriented language because: 1) Java [...]

What is java class file magic number

admins — Fri, 18 May 2012 14:52:30 +0000

Class file magic number is the number which is written at the starting of each class file. The java class loader checks for this number in order to identify whether a file is really a class file. This magic number is CAFEBABE. One can verify the existence of magic number by opening any class file [...]

How Unicode is used in Java

admins — Fri, 18 May 2012 14:50:24 +0000

Unicode is a standard to provide consistent encoding standard of characters for use in the text. Unicode uses 16 bits for encoding each character and hence has a large collection of characters. The visual attributes like font, size and height is left to the application/program using the Unicode standard. The Unicode standard has been widely [...]

What are the method overloading rules in java

admins — Fri, 18 May 2012 14:06:29 +0000

The rules of overloading are: 1) The name of method should be same for the overloaded methods. 2) The methods should differ either in the number of arguments or the type of arguments. Example Code: Here the three methods are differing in the number as well as the type of method arguments. 3) Overloaded methods [...]

Log4J File Appender Example

admins — Fri, 18 May 2012 10:00:52 +0000

When using the file based logging, there are many points to consider including the appender, rolling frequency, log level etc. In this log4j tutorial, we shall see how a typical log4j file appender looks like and how can we the logger to use different file appenders each appending logs to different log files. . The [...]

Why we cannot override static methods

admins — Fri, 18 May 2012 08:43:57 +0000

Since the static members are associated with the class and same single method is shared among all the instances of the class, there is no question of resolving method call at runtime based on the object on which method is invoked. Hence the subclass’s static method (a static method having same signature as super class’s [...]

What are the method overriding rules in java

admins — Fri, 18 May 2012 08:24:35 +0000

The rules of overriding are: 1) The overriding and overridden methods should have the same signature including the number and type of arguments 2) The overriding method should have compatible return type (implicitly cast able) with the overridden method. Example Code: Wrongly Overridden- Incompatible return type Base Class: Since a Number class’s object can not [...]

Java interpreter vs Java Compiler

admins — Wed, 16 May 2012 07:05:17 +0000

There are many languages which either makes use of interpreter or Compiler but not both. Java uses both and because of that only it is able to provide platform independence for applications. When we compile the code using javac, the compiler is used but when we issue the command java then the interpreter runs and [...]

What is multiple inheritance and how Java avoids it

admins — Wed, 16 May 2012 04:17:54 +0000

The diamond problem with multiple inheritance is that when a variable/method of a class is accessed which is inherited from two (or more than two) classes which declare the same variable/method then it becomes ambiguous as to which inherited variable/method should the derived class use since it has inherited multiple different implementations of the same [...]