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

@@ -23,10 +23,12 @@
  * questions.
  */
 
 package java.lang;
 
+import sun.misc.ConstantLengthCharSequence;
+
 import java.util.Arrays;
 
 /**
  * A thread-safe, mutable sequence of characters.
  * A string buffer is like a {@link String}, but can be modified. At any

@@ -344,10 +346,20 @@
         super.append(s);
         return this;
     }
 
     /**
+     * @since 1.9
+     */
+    @Override
+    synchronized StringBuffer append(ConstantLengthCharSequence ccs) {
+        toStringCache = null;
+        super.append(ccs);
+        return this;
+    }
+
+    /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since      1.5
      */
     @Override
     public synchronized StringBuffer append(CharSequence s, int start, int end)

@@ -541,10 +553,20 @@
         super.insert(dstOffset, s);
         return this;
     }
 
     /**
+     * @since 1.9
+     */
+    @Override
+    synchronized StringBuffer insert(int offset, ConstantLengthCharSequence ccs) {
+        toStringCache = null;
+        super.insert(offset, ccs);
+        return this;
+    }
+
+    /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since      1.5
      */
     @Override
     public synchronized StringBuffer insert(int dstOffset, CharSequence s,