8322512: StringBuffer.repeat does not work correctly after toString()…

… was called

Reviewed-by: prappo, redestad
Backport-of: df22fb322e6c4c9931a770bd0abf4c43b83c4e4a

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

@@ -715,6 +715,7 @@ public synchronized StringBuffer reverse() {
      */
     @Override
     public synchronized StringBuffer repeat(int codePoint, int count) {
+        toStringCache = null;
         super.repeat(codePoint, count);
         return this;
     }
@@ -726,6 +727,7 @@ public synchronized StringBuffer repeat(int codePoint, int count) {
      */
     @Override
     public synchronized StringBuffer repeat(CharSequence cs, int count) {
+        toStringCache = null;
         super.repeat(cs, count);
         return this;
     }

test/jdk/java/lang/StringBuilder/StringBufferRepeat.java

@@ -29,7 +29,7 @@
 
 /**
  * @test
- * @bug 8302323
+ * @bug 8302323 8322512
  * @summary Test StringBuffer.repeat sanity tests
  * @run testng/othervm -XX:-CompactStrings StringBufferRepeat
  * @run testng/othervm -XX:+CompactStrings StringBufferRepeat
@@ -129,6 +129,19 @@ public void sanity() {
         expected = "\u0000\u0000\u0000\u0000\u0000\u0000\u0020\u0020\u0020\u0020\u0020\u0020\u2461\u2462\u2462\u2462\u2462\u2462\udbff\udfff\udbff\udfff\udbff\udfff\udbff\udfff\udbff\udfff\udbff\udfff";
         assertEquals(expected, sb.toString());
 
+        // toStringCache
+
+        sb.setLength(0);
+        sb.toString();
+        sb.repeat('*', 5);
+        expected = "*****";
+        assertEquals(sb.toString(), expected);
+        sb.setLength(0);
+        sb.toString();
+        sb.repeat("*", 5);
+        assertEquals(sb.toString(), expected);
+
+
     }
 
     public void exceptions() {