RFR: 8290300: Use standard String-joining tools where applicable [v4]

[Сергей Цыпанов]

> Simplify code with `String.join()`

Сергей Цыпанов has updated the pull request incrementally with one additional commit since the last revision:

  8290300: Remove unused import

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9513/files
  - new: https://git.openjdk.org/jdk/pull/9513/files/4f2bbfd3..5b18c39c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9513&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9513&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 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