Fixed check style error.

apm-collector/apm-collector-agentstream/src/main/java/org/skywalking/apm/collector/agentstream/worker/segment/buffer/OffsetManager.java

@@ -142,11 +142,7 @@ public enum OffsetManager {
 
     class PrefixFileNameFilter implements FilenameFilter {
         @Override public boolean accept(File dir, String name) {
-            if (name.startsWith(OFFSET_FILE_PREFIX)) {
-                return true;
-            } else {
-                return false;
-            }
+            return name.startsWith(OFFSET_FILE_PREFIX);
         }
     }
 }

apm-collector/apm-collector-agentstream/src/main/java/org/skywalking/apm/collector/agentstream/worker/segment/buffer/SegmentBufferReader.java

@@ -141,11 +141,7 @@ public enum SegmentBufferReader {
 
     class PrefixFileNameFilter implements FilenameFilter {
         @Override public boolean accept(File dir, String name) {
-            if (name.startsWith(SegmentBufferManager.DATA_FILE_PREFIX)) {
-                return true;
-            } else {
-                return false;
-            }
+            return name.startsWith(SegmentBufferManager.DATA_FILE_PREFIX);
         }
     }
 }

apm-collector/apm-collector-agentstream/src/main/java/org/skywalking/apm/collector/agentstream/worker/segment/standardization/ReferenceIdExchanger.java

@@ -33,13 +33,13 @@ public class ReferenceIdExchanger implements IdExchanger<ReferenceDecorator> {
 
     private final Logger logger = LoggerFactory.getLogger(ReferenceIdExchanger.class);
 
-    private static ReferenceIdExchanger exchanger;
+    private static ReferenceIdExchanger EXCHANGER;
 
     public static ReferenceIdExchanger getInstance() {
-        if (exchanger == null) {
-            exchanger = new ReferenceIdExchanger();
+        if (EXCHANGER == null) {
+            EXCHANGER = new ReferenceIdExchanger();
         }
-        return exchanger;
+        return EXCHANGER;
     }
 
     @Override public boolean exchange(ReferenceDecorator standardBuilder, int applicationId) {

apm-collector/apm-collector-agentstream/src/main/java/org/skywalking/apm/collector/agentstream/worker/segment/standardization/SpanIdExchanger.java

@@ -28,13 +28,13 @@ import org.skywalking.apm.collector.core.util.StringUtils;
  */
 public class SpanIdExchanger implements IdExchanger<SpanDecorator> {
 
-    private static SpanIdExchanger exchanger;
+    private static SpanIdExchanger EXCHANGER;
 
     public static SpanIdExchanger getInstance() {
-        if (exchanger == null) {
-            exchanger = new SpanIdExchanger();
+        if (EXCHANGER == null) {
+            EXCHANGER = new SpanIdExchanger();
         }
-        return exchanger;
+        return EXCHANGER;
     }
 
     @Override public boolean exchange(SpanDecorator standardBuilder, int applicationId) {