src/java.base/share/classes/java/lang/Appendable.java

*** 116,121 ****
--- 116,146 ----
       *
       * @throws  IOException
       *          If an I/O error occurs
       */
      Appendable append(char c) throws IOException;
+ 
+     /**
+      * Appends {@code n} copies of the specified character to this
+      * {@code Appendable}.
+      *
+      * @param  c
+      *         The character to append
+      * @param  n
+      *         The number of copies
+      *
+      * @return  A reference to this {@code Appendable}
+      *
+      * @throws  IOException
+      *          If an I/O error occurs
+      * @throws  IllegalArgumentException
+      *          If {@code n} is negative
+      */
+     default Appendable appendN(char c, int n) throws IOException {
+         if (n < 0) {
+             throw new IllegalArgumentException("Negative number of"
+                     + " copies: " + n);
+         }
+         StringBuilder sb = new StringBuilder(n);
+         return append(sb.appendN(c, n));
+     }
  }