src/share/classes/java/util/StringJoiner.java

rev 7730 : 8020977: StringJoiner merges with itself not as expected
Reviewed-by: psandoz, chegar, mduigou, smarks

*** 204,218 ****
       * @throws NullPointerException if the other {@code StringJoiner} is null
       */
      public StringJoiner merge(StringJoiner other) {
          Objects.requireNonNull(other);
          if (other.value != null) {
              StringBuilder builder = prepareBuilder();
!             StringBuilder otherBuilder = other.value;
!             if (other.prefix.length() < otherBuilder.length()) {
!                 builder.append(otherBuilder, other.prefix.length(), otherBuilder.length());
!             }
          }
          return this;
      }
  
      private StringBuilder prepareBuilder() {
--- 204,219 ----
       * @throws NullPointerException if the other {@code StringJoiner} is null
       */
      public StringJoiner merge(StringJoiner other) {
          Objects.requireNonNull(other);
          if (other.value != null) {
+             final int length = other.value.length();
+             // lock the length so that we can seize the data to be appended
+             // before initiate copying to avoid interference, especially when
+             // merge 'this'
              StringBuilder builder = prepareBuilder();
!             builder.append(other.value, other.prefix.length(), length);
          }
          return this;
      }
  
      private StringBuilder prepareBuilder() {