This PR proposes to slightly improve some iterators of `AbstractMap`: * Code reuse * A field declared `final` * Add missing `@Override` annotations
------------- Commit messages: - Improve AbstractMap anonymous Iterator classes Changes: https://git.openjdk.org/jdk/pull/15615/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15615&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8315850 Stats: 76 lines in 1 file changed: 44 ins; 28 del; 4 mod Patch: https://git.openjdk.org/jdk/pull/15615.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/15615/head:pull/15615 PR: https://git.openjdk.org/jdk/pull/15615
