HDFS-16709. Remove redundant cast in FSEditLogOp.class

[ZanderXu]

Description of PR

When I read some class about Edits of NameNode, I found that there are much redundant cast in FSEditLogOp.class, I feel that we should remove them.

Such as:

static UpdateBlocksOp getInstance(OpInstanceCache cache) {
return (UpdateBlocksOp)cache.get(OP_UPDATE_BLOCKS);
}

Because cache.get() have cast the response to T, so we can remove the redundant cast.

@SuppressWarnings("unchecked")
public <T extends FSEditLogOp> T get(FSEditLogOpCodes opCode) {
return useCache ? (T)CACHE.get().get(opCode) : (T)newInstance(opCode);
} 

[slfan1989]

Can the unchecked flag be removed?

@SuppressWarnings("unchecked")
public <T extends FSEditLogOp> T get(FSEditLogOpCodes opCode) {
return useCache ? (T)CACHE.get().get(opCode) : (T)newInstance(opCode);
} 

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 54s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 1s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ trunk Compile Tests _
+1 💚	mvninstall	38m 30s		trunk passed
+1 💚	compile	1m 45s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	compile	1m 36s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	1m 27s		trunk passed
+1 💚	mvnsite	1m 50s		trunk passed
+1 💚	javadoc	1m 25s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	1m 47s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 43s		trunk passed
+1 💚	shadedclient	23m 21s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 24s		the patch passed
+1 💚	compile	1m 26s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javac	1m 26s		the patch passed
+1 💚	compile	1m 19s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	1m 19s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	1m 1s		the patch passed
+1 💚	mvnsite	1m 26s		the patch passed
+1 💚	javadoc	0m 58s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	1m 32s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 23s		the patch passed
+1 💚	shadedclient	22m 46s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	416m 26s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch passed.
+1 💚	asflicense	1m 17s		The patch does not generate ASF License warnings.
		527m 36s

Reason	Tests
Failed junit tests	hadoop.hdfs.server.blockmanagement.TestBlockTokenWithShortCircuitRead

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4667/1/artifact/out/Dockerfile
GITHUB PR	#4667
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux be082fe1e5d1 4.15.0-112-generic #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 6154108
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4667/1/testReport/
Max. process+thread count	3386 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4667/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[ZanderXu]

Thanks @slfan1989 for your review.

Can the unchecked flag be removed?

I think we need it. Because after removing it, the IDEA warns Unchecked cast:org.apache.hadoop.hdfs.server.namenode.FSEditLogOp to T.

[ayushtkn]

LGTM

[slfan1989]

@ZanderXu

I think we need it. Because after removing it, the IDEA warns Unchecked cast:org.apache.hadoop.hdfs.server.namenode.FSEditLogOp to T.

Thanks for the explanation, I have understood your changes.
LGTM.

[Hexiaoqiao]

LGTM. +1.

[ZanderXu]

@Hexiaoqiao@ayushtkn@goiri Master, can help me merge this PR into trunk? Thanks

[ZanderXu]

@slfan1989@Hexiaoqiao@goiri@ayushtkn Master, thank you very much for helping me review this patch.