Java Annotations - Starting Java 5.0

Other APIs require “side files” to be maintained in parallel with programs. For example JavaBeans requires a BeanInfo class to be maintained in parallel with a bean, and Enterprise JavaBeans (EJB) requires a deployment descriptor. It would be more convenient and less error-prone if the information in these side files were maintained as annotations in the program itself.

The Anwer --- Java Annotations...

The Java platform has always had various ad hoc annotation mechanisms. For example the transient modifier is an ad hoc annotation indicating that a field should be ignored by the serialization subsystem, and the @deprecated javadoc tag is an ad hoc annotation indicating that the method should no longer be used. As of release 5.0, the platform has a general purpose annotation (also known as metadata) facility that permits you to define and use your own annotation types. The facility consists of a syntax for declaring annotation types, a syntax for annotating declarations, APIs for reading annotations, a class file representation for annotations, and an annotation processing tool.

?: Shorthand for if-then statement

Example

Object = (Service != null)
? serviceobj.setValue(10)
: serviceobj = new ServiceClass();

Enum in Java 5.0

In 5.0, the Java™ programming language gets linguistic support for enumerated types. In their simplest form, these enums look just like their C, C++, and C# counterparts:

enum Season { WINTER, SPRING, SUMMER, FALL }

But appearances can be deceiving. Java programming language enums are far more powerful than their counterparts in other languages, which are little more than glorified integers. The new enum declaration defines a full-fledged class (dubbed an enum type). In addition to solving all the problems mentioned above, it allows you to add arbitrary methods and fields to an enum type, to implement arbitrary interfaces, and more. Enum types provide high-quality implementations of all the Object methods. They are Comparable and Serializable, and the serial form is designed to withstand arbitrary changes in the enum type.

POJO

POJO: Plain Old Java Object
Usually used in the context of frameworks, such as EJB, where there is too much bloat.