[LANG-403] HashcodeBuilder is broken for Annotations

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.3
• Fix Version/s: Patch Needed
• Component/s: lang.builder.*
• Assignee: Unassigned
• Reporter: Jay Liang
• Created: 24/Jan/08 16:58
• Updated: 21/Oct/13 05:38

Description

HashCodeBuilder does not produce a correct hashCode that conforms to java language specs. Running the following code snippets, i get

@Simple$CustomAnnotation(name=blah, type=class java.lang.String) hashCode= 895255138
Simple$CustomAnnotationImpl@665753[_name=blah,_type=class java.lang.String] hashCode= 122852694
hashCode should be 895255138

The hashCode should computed according to http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Annotation.html#hashCode() for annotations.

public class Simple{

  @Retention(RetentionPolicy.RUNTIME)
  @Target({FIELD, METHOD, PARAMETER})
  private @interface CustomAnnotation{

    public String name();
    public Class<?> type();
  }

  private static class CustomAnnotationImpl implements CustomAnnotation{
    final String _name;
    final Class<?> _type;

    public CustomAnnotationImpl(String name, Class<?> type) {
      _name = name;
      _type = type;
    }

    public String name() {
      return _name;
    }

    public Class<?> type() {
      return _type;
    }

    public Class<? extends Annotation> annotationType() {
      return CustomAnnotation.class;
    }

    @Override
    public int hashCode() {
      return HashCodeBuilder.reflectionHashCode(this);
    }

    /**
     * This conform to specs defined at http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Annotation.html#hashCode
     * @return good annotation hashCode
     */
    public int goodHashCode() {
      return (127 * "name".hashCode() ^ _name.hashCode()) + (127 *"type".hashCode() ^ _type.hashCode());
    }
    
    @Override
    public String toString() {
      return ToStringBuilder.reflectionToString(this);
    }

  }

  private static class Test{
    @CustomAnnotation(name="blah", type=String.class)
    String _blah;
    @Override
    public String toString() {
      return ToStringBuilder.reflectionToString(this);
    }
  }

  
  public static void main(String[] args) throws Exception{
    for(Field f : Test.class.getDeclaredFields()){
      for(Annotation a : f.getAnnotations()){
        System.out.println(a + " hashCode= " + a.hashCode());
        CustomAnnotationImpl c =  new Simple.CustomAnnotationImpl("blah", String.class);
        System.out.println(c + " hashCode= " + c.hashCode());
        System.out.println("hashCode should be "+ c.goodHashCode());
      }
    }
  }

}