RFR: 8274900: Too weak variable type leads to unnecessary cast in jdk.javadoc

[Andrey Turbanov]

There are several redundant casts, caused by fact, that related declared variable has too weak type.
We can change declaration type and remove redundant cast. It makes code more clear and easier to read.

Found by IntelliJ IDEA inspection 'Too weak variable type leads to unnecessary cast'

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Commit messages:
 - [PATCH] Cleanup redundant casts, when type is actually known beforehand

Changes: https://git.openjdk.java.net/jdk/pull/5636/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5636&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274900
  Stats: 15 lines in 3 files changed: 0 ins; 2 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5636.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5636/head:pull/5636

PR: https://git.openjdk.java.net/jdk/pull/5636