Project Valhalla's First Preview: JEP 401 Redefines == for Java Objects

JEP 401 has been merged into JDK 28 as a preview feature that introduces value objects, classes declared with a new `value` modifier. These classes differ from ordinary Java classes by having no identity, with all instance fields treated as final and required to be fully assigned before the object can be observed. The change is intended to let the JVM represent such objects without the usual heap allocation, reducing memory and GC costs. The language now enforces stricter construction rules: every field must be assigned during construction, and the bytecode verifier supplied by JEP 539 checks this at load time. Additionally, instance methods of a value class may not be synchronized, eliminating a source of hidden locks. Developers must add the `value` keyword to class definitions and adjust any synchronized methods accordingly. Equality semantics have been altered for value objects. The `==` operator, which previously compared only object references, now performs a recursive field-by-field comparison when both operands are instances of the same value class. This does not replace `equals`; the usual guidance to use `equals` for logical equality still applies because the internal re