Summary

Add record classes to the Java language. Record classes, a.k.a. records, allow the definition of shallowly immutable, transparent carriers for a fixed set of values, the record components.

Problem

Modeling data classes with the Java language is possible but users have to generate a lot of boilerplate to model even the simplest of them. There is also a lot of repetition implying a lot of places for bugs to hide. Users are forced to provide implementations for methods like: toString, equals and hashCode even when those implementations could be directly derived from the state of transparent data carriers and easy to generate automatically by a compiler.

Solution

The Java language will be enhanced by supporting record classes: a new construction for the definition of shallowly immutable, transparent carriers for a fixed set of values, its record components. These feature will constitute a preview feature (JEP 12) in Java SE 14.

Specification

diff -r fd51f02ef75c -r cba5b68a6424 src/jdk.compiler/share/classes/com/sun/source/tree/ClassTree.java
--- a/src/jdk.compiler/share/classes/com/sun/source/tree/ClassTree.java Mon Nov 18 16:30:21 2019 -0500
+++ b/src/jdk.compiler/share/classes/com/sun/source/tree/ClassTree.java Mon Nov 18 16:40:42 2019 -0500
@@ -29,7 +29,7 @@
 import javax.lang.model.element.Name;

 /**
- * A tree node for a class, interface, enum, or annotation
+ * A tree node for a class, interface, enum, record, or annotation
  * type declaration.
  *
  * For example:
@@ -44,6 +44,7 @@
  *
  * @jls 8.1 Class Declarations
  * @jls 8.9 Enum Types
+ * @jls 8.10 Record Types
  * @jls 9.1 Interface Declarations
  * @jls 9.6 Annotation Types
  *
diff -r fd51f02ef75c -r cba5b68a6424 src/jdk.compiler/share/classes/com/sun/source/tree/Tree.java
--- a/src/jdk.compiler/share/classes/com/sun/source/tree/Tree.java      Mon Nov 18 16:30:21 2019 -0500
+++ b/src/jdk.compiler/share/classes/com/sun/source/tree/Tree.java      Mon Nov 18 16:40:42 2019 -0500
@@ -644,6 +644,20 @@
         PROVIDES(ProvidesTree.class),

         /**
+         * {@preview Associated with records, a preview feature of the Java language.
+         *
+         *           This enum constant is associated with <i>records</i>, a preview
+         *           feature of the Java language. Preview features
+         *           may be removed in a future release, or upgraded to permanent
+         *           features of the Java language.}
+         *
+         * Used for instances of {@link ClassTree} representing records.
+         *
+         * @since 14
+         */
+        RECORD(ClassTree.class),
+
+        /**
          * Used for instances of {@link RequiresTree} representing
          * requires directives in a module declaration.
          */

In addition, proposed changes to the JLS are available at http://cr.openjdk.java.net/~gbierman/jep359/jep359-20191125/specs/records-jls.html