Sunday, January 24, 2016


Reference from oracle tutorial

Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate.
Annotations have a number of uses, among them:
  • Information for the compiler — Annotations can be used by the compiler to detect errors or suppress warnings.
  • Compile-time and deployment-time processing — Software tools can process annotation information to generate code, XML files, and so forth.
  • Runtime processing — Some annotations are available to be examined at runtime.

Used on

  • package
  • class
  • method
  • field

@Override  //mark as override function from super classes
public String toString(){

Take a look at declaration

public @interface Override {

@Deprecated   //out of date, not suggested use
Take a look at declaration

public @interface Deprecated {

@SuppressWarnings  //ignore warning when compile
public static void test(){
List list = new ArrayList();

Take a look at declaration

public @interface SuppressWarnings {
     * The set of warnings that are to be suppressed by the compiler in the
     * annotated element.  Duplicate names are permitted.  The second and
     * successive occurrences of a name are ignored.  The presence of
     * unrecognized warning names is not an error: Compilers must
     * ignore any warning names they do not recognize.  They are, however,
     * free to emit a warning if an annotation contains an unrecognized
     * warning name.
     * Compiler vendors should document the warning names they support in
     * conjunction with this annotation type. They are encouraged to cooperate
     * to ensure that the same names work across multiple compilers.
    String[] value();

See usage of Annotation:
Declare Annotation

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