javolution.lang

Annotation Type Constant

@Documented
@Inherited
@Target(value={TYPE,FIELD,METHOD,PARAMETER,LOCAL_VARIABLE})
@Retention(value=CLASS)
public @interface Constant

Indicates that the state of a class instance, a static field or a method return value / parameter will not change ever. For parameters tagged Constant, defensive copy is unnecessary.

 @Constant(comment="Immutable")
 class Polygon extends Shape  { 
     private Point2D[] vertices;
     public Polygon(@Constant Point2D... vertices) { 
         this.vertices = vertices; // No defensive copying required.
     }
     @Constant(comment="Unmodifiable View") 
     List<Point2D> getVertices() { 
         return ConstantTable.of(vertices); // Unmodifiable array wrapper. 
     }
 }

The constant annotation is primarily for API documentation purpose but static analyzers could also be used to detect constant rules violations.

 Polygon triangle = new Polygon(p1, p2, p3); // Ok, literals are always constant.
 Point2D[] vertices = new Point2D[] { p1, p2, p3 };
 triangle = new Polygon(vertices); // vertices is now assumed constant.
 vertices[0] = null; // Rule violation, modification after vertices has been assumed constant!    
 

Version:

6.1, February 2, 2014

Author:

Jean-Marie Dautelle

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String	comment Provides additional information (default "").
boolean	value Indicates if this element is constant (default true).

Element Detail

value

public abstract boolean value

Indicates if this element is constant (default true).

Default:

true

comment

public abstract String comment

Provides additional information (default "").

Default:

""