Java Annotation

Question

Hi,
Can any one please help with the following questions ?
What is Java Annotation and its applicability ?
How does its absence & presence makes difference ??
Thanks in advance.

Answer 1

Ronakgpatel wrote:
Hi,Thanx.
@Column(name = "Col1", nullable = true)
     public String getCol1() {
          return col1;
     }can you please explain me the code above ?
Thanks in advance.The compiler attaches a special object to the method with initialised properties. This doesn't affect the code of the method in any way. However according to the way @Column has been defined, it will usually be available via reflection. So (supposing this definition is in class MyClass) you might put:
Method m = MyClass.class.getMethod("getCol1", new Class[0]);
Column an = m.getAnnotation(Column.class);
if(an != null)
   System.out.println("Method " + m.getName() + " has column name " + an.name());For example some database software might look at the class, find all the getter methods with @Column annotations, and generate an insert statement to create a table row based on the contents of that class.
This is typically used for frameworks called (variously) Object-Relational Mappers.
Annotations are called meta-data because they typically add some information about the way data in a particular field is to be treated.