diff --git a/common/src/main/java/com/taobao/arthas/common/JavaVersionUtils.java b/common/src/main/java/com/taobao/arthas/common/JavaVersionUtils.java
index 603b189942..7887bd5c91 100644
--- a/common/src/main/java/com/taobao/arthas/common/JavaVersionUtils.java
+++ b/common/src/main/java/com/taobao/arthas/common/JavaVersionUtils.java
@@ -28,19 +28,19 @@ public static float javaVersion() {
     }
 
     public static boolean isJava6() {
-        return JAVA_VERSION_STR.equals("1.6");
+        return "1.6".equals(JAVA_VERSION_STR);
     }
 
     public static boolean isJava7() {
-        return JAVA_VERSION_STR.equals("1.7");
+        return "1.7".equals(JAVA_VERSION_STR);
     }
 
     public static boolean isJava8() {
-        return JAVA_VERSION_STR.equals("1.8");
+        return "1.8".equals(JAVA_VERSION_STR);
     }
 
     public static boolean isJava9() {
-        return JAVA_VERSION_STR.equals("9");
+        return "9".equals(JAVA_VERSION_STR);
     }
 
     public static boolean isLessThanJava9() {
diff --git a/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadSampler.java b/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadSampler.java
index 91fade566d..ee75954a7a 100644
--- a/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadSampler.java
+++ b/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadSampler.java
@@ -124,6 +124,7 @@ public int compare(ThreadVO o1, ThreadVO o2) {
 
         // Sort by CPU time : should be a rendering hint...
         Collections.sort(threads, new Comparator<ThreadVO>() {
+            @Override
             public int compare(ThreadVO o1, ThreadVO o2) {
                 long l1 = deltas.get(o1);
                 long l2 = deltas.get(o2);
diff --git a/core/src/main/java/com/taobao/arthas/core/util/FileUtils.java b/core/src/main/java/com/taobao/arthas/core/util/FileUtils.java
index ec046468cf..ac66a1cd49 100644
--- a/core/src/main/java/com/taobao/arthas/core/util/FileUtils.java
+++ b/core/src/main/java/com/taobao/arthas/core/util/FileUtils.java
@@ -42,20 +42,10 @@ public static void writeByteArrayToFile(File file, byte[] data) throws IOExcepti
      * @since IO 2.1
      */
     public static void writeByteArrayToFile(File file, byte[] data, boolean append) throws IOException {
-        OutputStream out = null;
-        try {
-            out = openOutputStream(file, append);
+        try (OutputStream out = openOutputStream(file, append)) {
             out.write(data);
-            out.close(); // don't swallow close Exception if copy completes normally
-        } finally {
-            try {
-                if (out != null) {
-                    out.close();
-                }
-            } catch (IOException ioe) {
-                // ignore
-            }
         }
+        // ignore
     }
 
     /**
@@ -111,10 +101,8 @@ private static boolean isAuthCommand(String command) {
      * @param file the file to save the history
      */
     public static void saveCommandHistory(List<int[]> history, File file) {
-        OutputStream out = null;
-        try {
-            out = new BufferedOutputStream(openOutputStream(file, false));
-            for (int[] command: history) {
+        try (OutputStream out = new BufferedOutputStream(openOutputStream(file, false))) {
+            for (int[] command : history) {
                 String commandStr = Helper.fromCodePoints(command);
                 if (isAuthCommand(commandStr)) {
                     command = AUTH_CODEPOINTS;
@@ -127,20 +115,13 @@ public static void saveCommandHistory(List<int[]> history, File file) {
             }
         } catch (IOException e) {
             // ignore
-        } finally {
-            try {
-                if (out != null) {
-                    out.close();
-                }
-            } catch (IOException ioe) {
-                // ignore
-            }
         }
+        // ignore
     }
 
     public static List<int[]> loadCommandHistory(File file) {
         BufferedReader br = null;
-        List<int[]> history = new ArrayList<int[]>();
+        List<int[]> history = new ArrayList<>();
         try {
             br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
             String line;
@@ -167,10 +148,8 @@ public static List<int[]> loadCommandHistory(File file) {
      * @param file the file to save the history
      */
     public static void saveCommandHistoryString(List<String> history, File file) {
-        OutputStream out = null;
-        try {
-            out = new BufferedOutputStream(openOutputStream(file, false));
-            for (String command: history) {
+        try (OutputStream out = new BufferedOutputStream(openOutputStream(file, false))) {
+            for (String command : history) {
                 if (!StringUtils.isBlank(command)) {
                     if (isAuthCommand(command)) {
                         command = ArthasConstants.AUTH;
@@ -181,20 +160,13 @@ public static void saveCommandHistoryString(List<String> history, File file) {
             }
         } catch (IOException e) {
             // ignore
-        } finally {
-            try {
-                if (out != null) {
-                    out.close();
-                }
-            } catch (IOException ioe) {
-                // ignore
-            }
         }
+        // ignore
     }
 
     public static List<String> loadCommandHistoryString(File file) {
         BufferedReader br = null;
-        List<String> history = new ArrayList<String>();
+        List<String> history = new ArrayList<>();
         try {
             br = new BufferedReader(new InputStreamReader(new FileInputStream(file), "utf-8"));
             String line;
@@ -218,8 +190,7 @@ public static List<String> loadCommandHistoryString(File file) {
     }
 
     public static String readFileToString(File file, Charset encoding) throws IOException {
-        FileInputStream stream = new FileInputStream(file);
-        try {
+        try (FileInputStream stream = new FileInputStream(file)) {
             Reader reader = new BufferedReader(new InputStreamReader(stream, encoding));
             StringBuilder builder = new StringBuilder();
             char[] buffer = new char[8192];
@@ -228,8 +199,6 @@ public static String readFileToString(File file, Charset encoding) throws IOExce
                 builder.append(buffer, 0, read);
             }
             return builder.toString();
-        } finally {
-            stream.close();
         }
     }