--- a/src/main/java/christie/blockchain/BlockHeader.java	Tue Jan 08 19:22:00 2019 +0900
+++ b/src/main/java/christie/blockchain/BlockHeader.java	Thu Jan 10 18:04:38 2019 +0900
@@ -21,7 +21,6 @@
 
     private long nonce;
 
-    HashUtil hashUtil = new HashUtil();
 
     public BlockHeader(byte[] parentHash, long difficulty, long number, long timestamp) {
         this.parentHash = parentHash;
@@ -63,7 +62,7 @@
 
     public byte[] getPresentHash() {
 
-        return hashUtil.sha256(getParamByteArray(true));
+        return HashUtil.sha256(getParamByteArray(true));
     }
 
     public byte[] getByteArrayWithoutNonce(){

--- a/src/main/java/christie/blockchain/ECKey.java	Tue Jan 08 19:22:00 2019 +0900
+++ b/src/main/java/christie/blockchain/ECKey.java	Thu Jan 10 18:04:38 2019 +0900
@@ -26,9 +26,6 @@
     private final PublicKey publicKey;
     private final Provider provider;
 
-    HashUtil hashUtil = new HashUtil();
-
-
     static {
         X9ECParameters params = SECNamedCurves.getByName("secp256k1");
         CURVE = new ECDomainParameters(params.getCurve(), params.getG(), params.getN(), params.getH());

--- a/src/main/java/christie/blockchain/HashUtil.java	Tue Jan 08 19:22:00 2019 +0900
+++ b/src/main/java/christie/blockchain/HashUtil.java	Thu Jan 10 18:04:38 2019 +0900
@@ -6,7 +6,7 @@
 
 
 public class HashUtil {
-    public byte[] sha256(byte[] input) {
+    public static byte[] sha256(byte[] input) {
         SHA256Digest digest = new SHA256Digest();
         byte[] resBuf = new byte[digest.getDigestSize()];
         if(input != null) {
@@ -19,7 +19,7 @@
 
     }
 
-    public byte[] sha3(byte[] input){
+    public static byte[] sha3(byte[] input){
         SHA3Digest digest = new SHA3Digest();
         byte[] resBuf = new byte[digest.getDigestSize()];
         if(input != null) {
@@ -32,7 +32,7 @@
 
     }
 
-    public byte[] ripemd160(byte[] input){
+    public static byte[] ripemd160(byte[] input){
         RIPEMD160Digest digest = new RIPEMD160Digest();
         byte[] resBuf = new byte[digest.getDigestSize()];
         if(input != null) {
@@ -44,7 +44,7 @@
         return resBuf;
     }
 
-    public byte[] sha3omit12(byte[] input) {
+    public static byte[] sha3omit12(byte[] input) {
         byte[] hash = sha3(input);
         return copyOfRange(hash, 12, hash.length);
     }

--- a/src/main/java/christie/blockchain/Miner.java	Tue Jan 08 19:22:00 2019 +0900
+++ b/src/main/java/christie/blockchain/Miner.java	Thu Jan 10 18:04:38 2019 +0900
@@ -10,9 +10,6 @@
 
 public class Miner {
 
-    HashUtil hashUtil = new HashUtil();
-
-
     public void mineBlock(Block newBlock, int difficulty) {
         long nonce = 0;
 
@@ -21,13 +18,13 @@
         String target = new String(new char[difficulty]).replace('\0', '0');
         byte[] hash = newBlock.getByteArrayWithoutNonce();
 
-        String hashStr = new String(hashUtil.sha256(hash), Charset.forName("utf-8"));
+        String hashStr = new String(HashUtil.sha256(hash), Charset.forName("utf-8"));
 
 
         while(!hashStr.substring( 0, difficulty).equals(target)) {
             nonce ++;
             byte[] concat = Arrays.concatenate(hash, BigInteger.valueOf(nonce).toByteArray());
-            hashStr = new String(hashUtil.sha256(concat), Charset.forName("utf-8"));
+            hashStr = new String(HashUtil.sha256(concat), Charset.forName("utf-8"));
         }
         newBlock.setNonce(nonce);
         System.out.println("Block Mined!!! : " + hashStr);

--- a/src/main/java/christie/blockchain/Transaction.java	Tue Jan 08 19:22:00 2019 +0900
+++ b/src/main/java/christie/blockchain/Transaction.java	Thu Jan 10 18:04:38 2019 +0900
@@ -22,8 +22,6 @@
 
     private byte[] signature;
 
-    HashUtil hashUtil = new HashUtil();
-
     ECKey ecKey = new ECKey();
 
 
@@ -69,7 +67,7 @@
 
     public byte[] gethash() {
 
-        return hashUtil.sha256(getParamByteArray());
+        return HashUtil.sha256(getParamByteArray());
     }
 
     public void generateSignature(PrivateKey privateKey) {