[jira] [Commented] (LANG-1062) Use Java 8 features to improve EqualsBuilder

["Alan Green (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LANG-1062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14598514#comment-14598514 ] 

Alan Green commented on LANG-1062:
----------------------------------

A couple of thoughts:

1. The attribute access functions could be applied to both objects in the equality, so append only needs one argument:

{code}
return EqualsBuilder.test(this, obj).append(o -> o.id).isEquals();
{code}

2. It would make sense to provide a single function that accepts a collection of attribute access functions:

{code}
return EqualsBuilder.test(this, obj).appendAll(Arrays.asList(o -> o.id, o -> o.name, o -> o.color)).isEquals();
{code}

3. Since the common case is for hashCode and equality to work over the same member attributes, they could share this list:

{code}
private static final List<Function<ThisClass, ?>> EQUAL_ATTRS = Arrays.asList(o -> o.id, o -> o.name, o -> o.color);

public boolean equals(final Object obj) {
  return EqualsBuilder.test(this, obj).appendAll(EQUAL_ATTRS).isEquals();
}

public int hashCode() {
  return HashCodeBuilder.for(this).appendAll(EQUAL_ATTRS).build();
}
{code}

> Use Java 8 features to improve EqualsBuilder
> --------------------------------------------
>
>                 Key: LANG-1062
>                 URL: https://issues.apache.org/jira/browse/LANG-1062
>             Project: Commons Lang
>          Issue Type: Improvement
>          Components: lang.builder.*
>    Affects Versions: 3.3.2
>            Reporter: Bruce Brouwer
>             Fix For: 4.0
>
>
> Remove the need for boilerplate code still necessary with EqualsBuilder. Instead of checking for instanceOf or equality checks, it would be nice to be able to write this:
> {code}
> public boolean equals(final Object obj) {
>   return EqualsBuilder.test(this, obj).append(this.id, o -> o.id).isEquals();
> }
> {code}
> I think this could generally work with a subclass of EqualsBuilder with a generic type, like this:
> {code}
> public class LambdaEqualsBuilder<T> extends EqualsBuilder {
>     private final T obj;
>     public LambdaEqualsBuilder(final T _this, final Object obj) {
>         if (_this != obj && !_this.getClass().isInstance(obj)) {
>             appendSuper(false);
>             this.obj = null;
>         } else {
>             this.obj = (T) obj;
>         }
>     }
>     public <P> LambdaEqualsBuilder<T> append(final P a, final Function<T, P> b) {
>         if (isEquals()) {
>             return (LambdaEqualsBuilder<T>) append(a, b.apply(obj));
>         }
>         return this;
>     }
>     // This might actually go in EqualsBuilder itself
>     public static <E> LambdaEqualsBuilder<E> test(final E _this, final Object _that) {
>         return new LambdaEqualsBuilder<E>(_this, _that);
>     }
> }
> {code}



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