RFR: 8290300: Use standard String-joining tools where applicable

[Сергей Цыпанов]

Simplify code with `String.join()`

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Commit messages:
 - 8290300: Fix copy-right year
 - 8290300: Use standard String-joining tools where applicable

Changes: https://git.openjdk.org/jdk/pull/9513/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9513&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290300
  Stats: 90 lines in 8 files changed: 1 ins; 68 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/9513.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9513/head:pull/9513

PR: https://git.openjdk.org/jdk/pull/9513