8016698: Cleanup overrides warning in sun/tools/ClassDeclaration.java

Summary: Override Object.hashCode()
Reviewed-by: alanb, chegar

src/share/classes/sun/tools/java/ClassDeclaration.java

@@ -230,12 +230,17 @@ class ClassDeclaration implements Constants {
      * Equality
      */
     public boolean equals(Object obj) {
-        if ((obj != null) && (obj instanceof ClassDeclaration)) {
+        if (obj instanceof ClassDeclaration) {
             return type.equals(((ClassDeclaration)obj).type);
         }
         return false;
     }
 
+    @Override
+    public int hashCode() {
+        return type.hashCode();
+    }
+
     /**
      * toString
      */