109: removed implementation coupling from Clock interface. DefaultClock.INSTANCE achieves the same thing without coupling.

src/main/java/io/jsonwebtoken/Clock.java

@@ -1,7 +1,5 @@
 package io.jsonwebtoken;
 
-import io.jsonwebtoken.impl.DefaultClock;
-
 import java.util.Date;
 
 /**
@@ -11,8 +9,6 @@ import java.util.Date;
  */
 public interface Clock {
 
-    public static final Clock DEFAULT = new DefaultClock();
-
     /**
      * Returns the clock's current timestamp at the instant the method is invoked.
      *

src/main/java/io/jsonwebtoken/impl/DefaultClock.java

@@ -11,6 +11,11 @@ import java.util.Date;
  */
 public class DefaultClock implements Clock {
 
+    /**
+     * Default static instance that may be shared.  It is thread-safe.
+     */
+    public static final Clock INSTANCE = new DefaultClock();
+
     /**
      * Simply returns <code>new {@link Date}()</code>.
      *

src/main/java/io/jsonwebtoken/impl/DefaultJwtParser.java

@@ -70,7 +70,7 @@ public class DefaultJwtParser implements JwtParser {
 
     Claims expectedClaims = new DefaultClaims();
 
-    private Clock clock = Clock.DEFAULT;
+    private Clock clock = DefaultClock.INSTANCE;
 
     @Override
     public JwtParser requireIssuedAt(Date issuedAt) {