diff --git a/src/org/jcodings/MultiByteEncoding.java b/src/org/jcodings/MultiByteEncoding.java
index a667165..f2d7d85 100644
--- a/src/org/jcodings/MultiByteEncoding.java
+++ b/src/org/jcodings/MultiByteEncoding.java
@@ -201,6 +201,7 @@ protected final boolean mb4IsCodeCType(int code, int ctype) {
     }
 
     /* onigenc_strlen */
+    @Override
     public int strLength(byte[]bytes, int p, int end) {
         int n = 0;
         int q = p;
@@ -211,6 +212,7 @@ public int strLength(byte[]bytes, int p, int end) {
         return n;
     }
 
+    @Override
     public int strCodeAt(byte[]bytes, int p, int end, int index) {
         int n = 0;
         int q = p;
diff --git a/src/org/jcodings/exception/CharacterPropertyException.java b/src/org/jcodings/exception/CharacterPropertyException.java
index 59c660a..f628d10 100644
--- a/src/org/jcodings/exception/CharacterPropertyException.java
+++ b/src/org/jcodings/exception/CharacterPropertyException.java
@@ -21,7 +21,9 @@
 
 public class CharacterPropertyException extends EncodingException {
 
-    public CharacterPropertyException(EncodingError error) {
+   private static final long serialVersionUID = 1L;
+
+   public CharacterPropertyException(EncodingError error) {
         super(error);
     }
 
diff --git a/src/org/jcodings/exception/EncodingException.java b/src/org/jcodings/exception/EncodingException.java
index 592cae8..f85d8d3 100644
--- a/src/org/jcodings/exception/EncodingException.java
+++ b/src/org/jcodings/exception/EncodingException.java
@@ -20,6 +20,9 @@
 package org.jcodings.exception;
 
 public class EncodingException extends JCodingsException {
+
+    private static final long serialVersionUID = 1L;
+
     private final EncodingError error;
 
     public EncodingException(EncodingError error) {
diff --git a/src/org/jcodings/exception/JCodingsException.java b/src/org/jcodings/exception/JCodingsException.java
index bd42cc4..a8d77a9 100644
--- a/src/org/jcodings/exception/JCodingsException.java
+++ b/src/org/jcodings/exception/JCodingsException.java
@@ -20,6 +20,9 @@
 package org.jcodings.exception;
 
 public class JCodingsException extends RuntimeException {
+
+    private static final long serialVersionUID = 1L;
+
     public JCodingsException(String message) {
         super(message);
     }
diff --git a/src/org/jcodings/exception/TranscoderException.java b/src/org/jcodings/exception/TranscoderException.java
index a4beea8..dda56cd 100644
--- a/src/org/jcodings/exception/TranscoderException.java
+++ b/src/org/jcodings/exception/TranscoderException.java
@@ -20,6 +20,9 @@
 package org.jcodings.exception;
 
 public class TranscoderException extends JCodingsException {
+
+    private static final long serialVersionUID = 1L;
+
     public TranscoderException(String message) {
         super(message);
     }
diff --git a/src/org/jcodings/specific/BaseEUCJPEncoding.java b/src/org/jcodings/specific/BaseEUCJPEncoding.java
index 2b007b3..f5390ce 100644
--- a/src/org/jcodings/specific/BaseEUCJPEncoding.java
+++ b/src/org/jcodings/specific/BaseEUCJPEncoding.java
@@ -92,6 +92,7 @@ public int mbcCaseFold(int flag, byte[]bytes, IntHolder pp, int end, byte[]lower
         }
     }
 
+    @Override
     protected boolean isLead(int c) {
         return ((c - 0xa1) & 0xff) > 0xfe - 0xa1;
     }
diff --git a/src/org/jcodings/specific/EUCKREncoding.java b/src/org/jcodings/specific/EUCKREncoding.java
index 924fbe4..8247ae5 100644
--- a/src/org/jcodings/specific/EUCKREncoding.java
+++ b/src/org/jcodings/specific/EUCKREncoding.java
@@ -69,6 +69,7 @@ public boolean isCodeCType(int code, int ctype) {
     }
 
     // euckr_islead
+    @Override
     protected boolean isLead(int c) {
         return ((c) < 0xa1 || (c) == 0xff);
     }
diff --git a/src/org/jcodings/specific/EmacsMuleEncoding.java b/src/org/jcodings/specific/EmacsMuleEncoding.java
index a3198db..165ccac 100644
--- a/src/org/jcodings/specific/EmacsMuleEncoding.java
+++ b/src/org/jcodings/specific/EmacsMuleEncoding.java
@@ -99,7 +99,7 @@ public int leftAdjustCharHead(byte[] bytes, int p, int s, int end) {
         int p_ = s;
         while (!islead(bytes[p_] & 0xff) && p_ > p) p_--;
         return p_;
-    };
+    }
 
     @Override
     public boolean isReverseMatchAllowed(byte[]bytes, int p, int end) {
diff --git a/src/org/jcodings/specific/GB18030Encoding.java b/src/org/jcodings/specific/GB18030Encoding.java
index e2f9cc1..e68ed67 100644
--- a/src/org/jcodings/specific/GB18030Encoding.java
+++ b/src/org/jcodings/specific/GB18030Encoding.java
@@ -120,7 +120,7 @@ private enum State {
         Odd_CM_Odd_C4CM,
         Even_CM_Even_C4CM,
         Odd_CM_Even_C4CM
-    };
+    }
 
     @Override
     public int leftAdjustCharHead(byte[]bytes, int start, int s, int end) {
diff --git a/src/org/jcodings/specific/Windows_1251Encoding.java b/src/org/jcodings/specific/Windows_1251Encoding.java
index 4f4f0e2..007ec1d 100644
--- a/src/org/jcodings/specific/Windows_1251Encoding.java
+++ b/src/org/jcodings/specific/Windows_1251Encoding.java
@@ -21,7 +21,6 @@
 
 import org.jcodings.CaseFoldMapEncoding;
 import org.jcodings.Config;
-import org.jcodings.ISOEncoding;
 import org.jcodings.IntHolder;
 import org.jcodings.constants.CharacterType;
 
diff --git a/src/org/jcodings/spi/Charsets.java b/src/org/jcodings/spi/Charsets.java
index beec046..7e73931 100644
--- a/src/org/jcodings/spi/Charsets.java
+++ b/src/org/jcodings/spi/Charsets.java
@@ -10,10 +10,13 @@
  */
 public class Charsets extends java.nio.charset.spi.CharsetProvider {
     private static final List<Charset> charsets = Collections.singletonList((Charset) ISO_8859_16.INSTANCE);
+
+    @Override
     public Iterator<Charset> charsets() {
         return charsets.iterator();
     }
 
+    @Override
     public Charset charsetForName(String charsetName) {
         if ("ISO-8859-16".equals(charsetName) || ISO_8859_16.INSTANCE.aliases().contains(charsetName)) {
             return ISO_8859_16.INSTANCE;
diff --git a/src/org/jcodings/transcode/EConv.java b/src/org/jcodings/transcode/EConv.java
index 5ca95b5..1197127 100644
--- a/src/org/jcodings/transcode/EConv.java
+++ b/src/org/jcodings/transcode/EConv.java
@@ -851,7 +851,6 @@ public boolean equals(Object other) {
         EConv ec2 = (EConv)other;
         int i;
 
-        if (ec2 == null) return false;
         if (ec1.source != ec2.source &&
                 !Arrays.equals(ec1.source, ec2.source))
             return false;
diff --git a/src/org/jcodings/transcode/TranscoderDB.java b/src/org/jcodings/transcode/TranscoderDB.java
index 1d6b38a..e944b69 100644
--- a/src/org/jcodings/transcode/TranscoderDB.java
+++ b/src/org/jcodings/transcode/TranscoderDB.java
@@ -219,6 +219,7 @@ private static EConv open0(byte[] source, byte[] destination, int ecflags) {
             numTrans = searchPath(source, destination, new SearchPathCallback() {
                 int additional = 0;
 
+                @Override
                 public void call(byte[] source, byte[] destination, int depth) {
                     if (lentries.p == null) lentries.p = new Entry[depth + 1 + additional];
                     lentries.p[depth] = getEntry(source, destination);
diff --git a/src/org/jcodings/transcode/TranscoderList.java b/src/org/jcodings/transcode/TranscoderList.java
index a3e6498..9b6f2f7 100644
--- a/src/org/jcodings/transcode/TranscoderList.java
+++ b/src/org/jcodings/transcode/TranscoderList.java
@@ -223,7 +223,7 @@ static void load() {
         TranscoderDB.declare("UTF-32", "UTF-8", "From_UTF_32");
         TranscoderDB.declare("UTF-8", "UTF-16", "To_UTF_16");
         TranscoderDB.declare("UTF-8", "UTF-32", "To_UTF_32");
-    };
+    }
 
     static final GenericTranscoderEntry[] GENERIC_LIST = new GenericTranscoderEntry[] {
         new GenericTranscoderEntry("Big5", "UTF-8", 57100, "Big5", 1, 2, 1, AsciiCompatibility.CONVERTER, 0),
diff --git a/src/org/jcodings/transcode/specific/Cp50220_decoder_Transcoder.java b/src/org/jcodings/transcode/specific/Cp50220_decoder_Transcoder.java
index 52060d6..6d0a812 100644
--- a/src/org/jcodings/transcode/specific/Cp50220_decoder_Transcoder.java
+++ b/src/org/jcodings/transcode/specific/Cp50220_decoder_Transcoder.java
@@ -40,6 +40,7 @@ public int stateFinish(byte[] state) {
         return TranscodeFunctions.iso2022jpInit(state);
     }
 
+    @Override
     public int startToInfo(byte[] statep, byte[] s, int sStart, int l) {
         return TranscodeFunctions.funSiCp50221Decoder(statep, s, sStart, l);
     }
diff --git a/src/org/jcodings/transcode/specific/Cp50221_decoder_Transcoder.java b/src/org/jcodings/transcode/specific/Cp50221_decoder_Transcoder.java
index 78fb56b..b279a24 100644
--- a/src/org/jcodings/transcode/specific/Cp50221_decoder_Transcoder.java
+++ b/src/org/jcodings/transcode/specific/Cp50221_decoder_Transcoder.java
@@ -40,6 +40,7 @@ public int stateFinish(byte[] state) {
         return TranscodeFunctions.iso2022jpInit(state);
     }
 
+    @Override
     public int startToInfo(byte[] statep, byte[] s, int sStart, int l) {
         return TranscodeFunctions.funSiCp50221Decoder(statep, s, sStart, l);
     }
diff --git a/src/org/jcodings/transcode/specific/Iso2022jp_decoder_Transcoder.java b/src/org/jcodings/transcode/specific/Iso2022jp_decoder_Transcoder.java
index a5fedba..41a562e 100644
--- a/src/org/jcodings/transcode/specific/Iso2022jp_decoder_Transcoder.java
+++ b/src/org/jcodings/transcode/specific/Iso2022jp_decoder_Transcoder.java
@@ -40,6 +40,7 @@ public int stateFinish(byte[] state) {
         return TranscodeFunctions.iso2022jpInit(state);
     }
 
+    @Override
     public int startToInfo(byte[] statep, byte[] s, int sStart, int l) {
         return TranscodeFunctions.funSiIso50220jpDecoder(statep, s, sStart, l);
     }
diff --git a/src/org/jcodings/transcode/specific/Iso2022jp_kddi_decoder_Transcoder.java b/src/org/jcodings/transcode/specific/Iso2022jp_kddi_decoder_Transcoder.java
index 57c7eda..001feb3 100644
--- a/src/org/jcodings/transcode/specific/Iso2022jp_kddi_decoder_Transcoder.java
+++ b/src/org/jcodings/transcode/specific/Iso2022jp_kddi_decoder_Transcoder.java
@@ -40,6 +40,7 @@ public int stateFinish(byte[] state) {
         return TranscodeFunctions.iso2022jpKddiInit(state);
     }
 
+    @Override
     public int startToInfo(byte[] statep, byte[] s, int sStart, int l) {
         return TranscodeFunctions.funSiIso2022jpKddiDecoder(statep, s, sStart, l);
     }
diff --git a/src/org/jcodings/util/ArrayReader.java b/src/org/jcodings/util/ArrayReader.java
index 5050c25..e07822e 100644
--- a/src/org/jcodings/util/ArrayReader.java
+++ b/src/org/jcodings/util/ArrayReader.java
@@ -44,12 +44,17 @@ public static byte[] readByteArray(String name) {
                 bytes[i] = dis.readByte();
             }
             checkAvailable(dis, name);
-            dis.close();
             return bytes;
         } catch (IOException ioe) {
             decorate(ioe, name);
-            return null;
+        } finally {
+            try {
+                dis.close();
+            } catch (IOException ex) {
+                // ignore
+            }
         }
+        return null;
     }
 
     public static int[] readIntArray(String name) {
@@ -61,12 +66,17 @@ public static int[] readIntArray(String name) {
                 ints[i] = dis.readInt();
             }
             checkAvailable(dis, name);
-            dis.close();
             return ints;
         } catch (IOException ioe) {
             decorate(ioe, name);
-            return null;
-        }
+        } finally {
+            try {
+                dis.close();
+            } catch (IOException ex) {
+                // ignore
+            }
+       }
+       return null;
     }
 
     public static int[][] readNestedIntArray(String name) {
@@ -82,14 +92,18 @@ public static int[][] readNestedIntArray(String name) {
                     iints[k] = dis.readInt();
                 }
             }
-
             checkAvailable(dis, name);
-            dis.close();
             return ints;
         } catch (IOException ioe) {
             decorate(ioe, name);
-            return null;
+        } finally {
+            try {
+                dis.close();
+            } catch (IOException ex) {
+                // ignore
+            }
         }
+        return null;
     }
 
     static void checkAvailable(DataInputStream dis, String name) throws IOException {
diff --git a/src/org/jcodings/util/BytesHash.java b/src/org/jcodings/util/BytesHash.java
index 3aeb11c..7237735 100644
--- a/src/org/jcodings/util/BytesHash.java
+++ b/src/org/jcodings/util/BytesHash.java
@@ -29,6 +29,7 @@ public BytesHash(int size) {
         super(size);
     }
 
+    @Override
     protected void init() {
         head = new BytesHashEntry<V>();
     }
@@ -62,7 +63,7 @@ public boolean equals(byte[]bytes, int p, int end) {
 
     public static int hashCode(byte[]bytes, int p, int end) {
         int key = 0;
-        while (p < end) key = ((key << 16) + (key << 6) - key) + (int)(bytes[p++]); // & 0xff ? we have to match jruby string hash
+        while (p < end) key = ((key << 16) + (key << 6) - key) + bytes[p++]; // & 0xff ? we have to match jruby string hash
         key = key + (key >> 5);
         return key;
     }
diff --git a/src/org/jcodings/util/CaseInsensitiveBytesHash.java b/src/org/jcodings/util/CaseInsensitiveBytesHash.java
index 6f30eb8..248ef39 100644
--- a/src/org/jcodings/util/CaseInsensitiveBytesHash.java
+++ b/src/org/jcodings/util/CaseInsensitiveBytesHash.java
@@ -31,6 +31,7 @@ public CaseInsensitiveBytesHash(int size) {
         super(size);
     }
 
+    @Override
     protected void init() {
         head = new CaseInsensitiveBytesHashEntry<V>();
     }
@@ -60,7 +61,7 @@ public boolean equals(byte[]bytes, int p, int end) {
 
     public static int hashCode(byte[]bytes, int p, int end) {
         int key = 0;
-        while (p < end) key = ((key << 16) + (key << 6) - key) + (int)(ToLowerCaseTable[bytes[p++] & 0xff]); // & 0xff ? we have to match jruby string hash
+        while (p < end) key = ((key << 16) + (key << 6) - key) + ToLowerCaseTable[bytes[p++] & 0xff]; // & 0xff ? we have to match jruby string hash
         key = key + (key >> 5);
         return key;
     }
diff --git a/src/org/jcodings/util/Hash.java b/src/org/jcodings/util/Hash.java
index 227aa0e..e973018 100644
--- a/src/org/jcodings/util/Hash.java
+++ b/src/org/jcodings/util/Hash.java
@@ -133,6 +133,7 @@ protected static int hashValue(int h) {
         return h & HASH_SIGN_BIT_MASK;
     }
 
+    @Override
     public Iterator<V> iterator() {
         return new HashIterator();
     }
@@ -144,16 +145,19 @@ public HashIterator() {
             next = head.after;
         }
 
+        @Override
         public boolean hasNext() {
             return next != head;
         }
 
+        @Override
         public V next() {
             HashEntry<V> e = next;
             next = e.after;
             return e.value;
         }
 
+        @Override
         public void remove() {
             throw new InternalException("not supported operation exception");
         }
@@ -170,20 +174,24 @@ public HashEntryIterator() {
             next = head.after;
         }
 
+        @Override
         public Iterator<HashEntry<V>> iterator() {
             return this;
         }
 
+        @Override
         public boolean hasNext() {
             return next != head;
         }
 
+        @Override
         public HashEntry<V> next() {
             HashEntry<V> e = next;
             next = e.after;
             return e;
         }
 
+        @Override
         public void remove() {
             throw new InternalException("not supported operation exception");
         }
diff --git a/src/org/jcodings/util/IntArrayHash.java b/src/org/jcodings/util/IntArrayHash.java
index 22e1f5f..e9b588b 100644
--- a/src/org/jcodings/util/IntArrayHash.java
+++ b/src/org/jcodings/util/IntArrayHash.java
@@ -29,6 +29,7 @@ public IntArrayHash(int size) {
         super(size);
     }
 
+    @Override
     protected void init() {
         head = new IntArrayHashEntry<V>();
     }
diff --git a/src/org/jcodings/util/IntHash.java b/src/org/jcodings/util/IntHash.java
index 9b0c1eb..20d6da7 100644
--- a/src/org/jcodings/util/IntHash.java
+++ b/src/org/jcodings/util/IntHash.java
@@ -29,6 +29,7 @@ public IntHash(int size) {
         super(size);
     }
 
+    @Override
     protected void init() {
         head = new IntHashEntry<V>();
     }
diff --git a/src/org/jcodings/util/ObjHash.java b/src/org/jcodings/util/ObjHash.java
index 0403d0a..8b96020 100644
--- a/src/org/jcodings/util/ObjHash.java
+++ b/src/org/jcodings/util/ObjHash.java
@@ -21,6 +21,7 @@
 
 public final class ObjHash<K, V> extends Hash<V> {
 
+   @Override
     protected void init() {
         head = new ObjHashEntry<K, V>();
     }
@@ -38,6 +39,7 @@ public ObjHashEntry() {
             key = null;
         }
 
+        @Override
         public boolean equals(Object key) {
             if (this.key == key) return true;
             return this.key.equals(key);
diff --git a/test/org/jcodings/specific/TestBig5.java b/test/org/jcodings/specific/TestBig5.java
index fdba5f1..7d5a10b 100755
--- a/test/org/jcodings/specific/TestBig5.java
+++ b/test/org/jcodings/specific/TestBig5.java
@@ -5,7 +5,6 @@
 
 import java.nio.charset.Charset;
 
-import org.jcodings.specific.BIG5Encoding;
 import org.junit.Test;
 
 public class TestBig5 {
diff --git a/test/org/jcodings/specific/TestCESU8.java b/test/org/jcodings/specific/TestCESU8.java
index ae8fe99..62e7fe8 100644
--- a/test/org/jcodings/specific/TestCESU8.java
+++ b/test/org/jcodings/specific/TestCESU8.java
@@ -1,11 +1,8 @@
 package org.jcodings.specific;
 
-import static junit.framework.Assert.assertEquals;
-import static junit.framework.Assert.assertTrue;
+import static org.junit.Assert.assertEquals;
 
 import org.jcodings.Encoding;
-import org.jcodings.constants.CharacterType;
-import java.nio.charset.StandardCharsets;
 import org.junit.Test;
 
 public class TestCESU8 {
diff --git a/test/org/jcodings/specific/TestCaseMap.java b/test/org/jcodings/specific/TestCaseMap.java
index 5c4c586..9ad7e5d 100644
--- a/test/org/jcodings/specific/TestCaseMap.java
+++ b/test/org/jcodings/specific/TestCaseMap.java
@@ -1,6 +1,6 @@
 package org.jcodings.specific;
 
-import static junit.framework.Assert.assertTrue;
+import static org.junit.Assert.assertTrue;
 
 import java.util.Arrays;
 import java.util.List;
diff --git a/test/org/jcodings/specific/TestEConvResult.java b/test/org/jcodings/specific/TestEConvResult.java
index dc02fdb..5676749 100644
--- a/test/org/jcodings/specific/TestEConvResult.java
+++ b/test/org/jcodings/specific/TestEConvResult.java
@@ -1,14 +1,15 @@
 package org.jcodings.specific;
 
-import junit.framework.Assert;
+import static org.junit.Assert.assertEquals;
+
 import org.jcodings.transcode.EConvResult;
 import org.junit.Test;
 
 public class TestEConvResult {
     @Test
     public void testSymbolicName() {
-        Assert.assertEquals("finished", EConvResult.Finished.symbolicName());
-        Assert.assertEquals("after_output", EConvResult.AfterOutput.symbolicName());
-        Assert.assertEquals("destination_buffer_full", EConvResult.DestinationBufferFull.symbolicName());
+        assertEquals("finished", EConvResult.Finished.symbolicName());
+        assertEquals("after_output", EConvResult.AfterOutput.symbolicName());
+        assertEquals("destination_buffer_full", EConvResult.DestinationBufferFull.symbolicName());
     }
 }
diff --git a/test/org/jcodings/specific/TestEmacsMule.java b/test/org/jcodings/specific/TestEmacsMule.java
index 9bd983d..68253ab 100644
--- a/test/org/jcodings/specific/TestEmacsMule.java
+++ b/test/org/jcodings/specific/TestEmacsMule.java
@@ -1,14 +1,13 @@
 package org.jcodings.specific;
 
 import static org.junit.Assert.assertEquals;
-import org.jcodings.specific.EmacsMuleEncoding;
 import org.junit.Test;
 
 public class TestEmacsMule {
     @Test
     public void testRightAdjustCharHeadAscii() {
         byte[] str = new byte[]{(byte)'a', (byte)'b', (byte)'c', (byte)',', (byte)'d', (byte)'e', (byte)'f'};
-        
+
         int t = EmacsMuleEncoding.INSTANCE.rightAdjustCharHead(str, 0, 3, 7);
         assertEquals("rightAdjustCharHead did not adjust properly", 3, t);
     }
diff --git a/test/org/jcodings/specific/TestGBK.java b/test/org/jcodings/specific/TestGBK.java
index 03a6f33..fa541df 100755
--- a/test/org/jcodings/specific/TestGBK.java
+++ b/test/org/jcodings/specific/TestGBK.java
@@ -8,7 +8,6 @@
 import org.jcodings.Encoding;
 import org.jcodings.EncodingDB;
 import org.jcodings.EncodingDB.Entry;
-import org.jcodings.specific.GBKEncoding;
 import org.jcodings.util.CaseInsensitiveBytesHash;
 import org.junit.Before;
 import org.junit.Test;
diff --git a/test/org/jcodings/specific/TestUnicode.java b/test/org/jcodings/specific/TestUnicode.java
index 34c2ea7..08a8784 100644
--- a/test/org/jcodings/specific/TestUnicode.java
+++ b/test/org/jcodings/specific/TestUnicode.java
@@ -1,7 +1,7 @@
 package org.jcodings.specific;
 
-import static junit.framework.Assert.assertEquals;
-import static junit.framework.Assert.assertTrue;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 import org.jcodings.Encoding;
 import org.jcodings.constants.CharacterType;