[24] JEP 492: Flexible Constructor Bodies (Third Preview)

[mpalat]

ref: https://openjdk.org/jeps/492
JLS Changes: https://cr.openjdk.org/~gbierman/jep492/latest/
https://bugs.openjdk.org/browse/JDK-8338287

Summary
In constructors in the Java programming language, allow statements to appear before an explicit constructor invocation, i.e., super(..) or this(..). The statements cannot reference the instance under construction, but they can initialize its fields. Initializing fields before invoking another constructor makes a class more reliable when methods are overridden. This is a preview language feature.

History
This feature was originally proposed by JEP 447, and delivered as a preview feature in JDK 22. JEP 482 was the second preview and the support of the same is captured in jdt.core issue #2472

[mpalat]

@stephan-herrmann assigning to you since you had done the earlier part. Please feel free to reassign

[stephan-herrmann]

JLS changes will be done via https://bugs.openjdk.org/browse/JDK-8338289 (which is still empty as of today :) ).

[stephan-herrmann]

We have a spec draft: https://cr.openjdk.org/~gbierman/jep492/jep492-20241101/specs/flexible-constructor-bodies-jls.html - said to contain only a small number of minor bug fixes.

[stephan-herrmann]

Currently, JLS changes can be found in https://cr.openjdk.org/~gbierman/jep492/jep492-20241101/specs/flexible-constructor-bodies-jls.html

[mpalat]

Currently, JLS changes can be found in https://cr.openjdk.org/~gbierman/jep492/jep492-20241101/specs/flexible-constructor-bodies-jls.html

The moving latest link: https://cr.openjdk.org/~gbierman/jep492/latest/

[stephan-herrmann]

Related issues:

• [23] VerifyError when instantiating a local class inside a flexible constructor #3115
• [23] Flow analysis ignores assigment in pre constructor context #3116

[stephan-herrmann]

Sub-issues are mined from https://bugs.openjdk.org/browse/JDK-8333313?jql=labels%20%3D%20javac-pre-capture%20ORDER%20BY%20status%20ASC

There may be more, still. I'm done with that list 😄

[stephan-herrmann]

Done here (until more bug reports come our way 😄)!